AM/FM radio troubleshooting

K

klem kedidelhopper

Guest
I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny
 
"klem kedidelhopper has six toes "
I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny
Click to expand...

** Might be another dodgy chemical fuse - eh ??



..... Phil
 
On May 20, 3:21 pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:
I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently.  Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is
Click to expand...
Somehow I feel looking at an oscilloscope might help with determining
the amplitude of the signal.

and I would hate to blow up an otherwise good IF amplifier with
an excessive signal.
Click to expand...
Somehow I feel that an excessive signal could be tamed with a resistor
divider circuit. Knowing what the input impedance of IF circuits is
might help.


I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand?  Thanks very much for any advice. Lenny
Click to expand...
One source of IF signal might be another FM radio. Just a wild, crazy
thought.

Further, if this is an AM-FM as the subject header states, you forgot
to mention if the AM worked.
 
klem kedidelhopper <captainvideo462009@gmail.com> wrote in message
news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com...
I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny
Click to expand...

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try
 
One might reasonably assume that the IF signal would not have a peak-to-peak
value larger than the net forward bias on the IF transistors. You can be
reasonably certain a signal of that level will not damage the transistors.
 
On May 20, 3:21 pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:
I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently.  Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand?  Thanks very much for any advice. Lenny
Click to expand...
I would first look at mechanical failure of the connections. ...PCB/
traces/etc.

Especially around the FM Detector area where you heat shocked the PCB
when changing that transistor.

I know it's hard to believe battery can heat that much but with age on
a PCB, you'd be surprised. Ever try cold spray when radio failed?
 
On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com...



I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently.  Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand?  Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try
Click to expand...
Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage that
doesn't really help me to track this down. I could look at the CW
signal from the 249 with my 50MHZ. scope or my spectrum analyzer but I
still don't know what a safe signal amplitude would be. Does anyone
know what the proper typical amplitude of an IF signal would be so
that I would be able to simulate this and inject this signal into the
IF amplifiers and detector stage? BTW except for the outputs, they're
all 4 pin GE transistors. What do you mean by the "simple fudge"?
Thanks, Lenny
 
"klem kedidelhopper" <captainvideo462009@gmail.com> wrote in message
news:61935a1d-3c6e-424a-893e-6e1f36ce8608@g3g2000vbl.googlegroups.com...
On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com...



I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try
Click to expand...
Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage

Does it have the old TO7 transistors like OC170/171/AF116/117 etc?

They're prone to internal whiskering, most commonly the can/screen to one of
the 3 electrodes, lifting the screen lead might get it going, some people
zap the whiskers with 47uF charged to 50V (twist C,B & E together first).

If the whiskers have reached 2 or more electrodes you're pretty much
stuffed, some people use BF450/451 as replacements but you usually have to
tweak the base bias resistors to suit silicon 0.7V and you might have to
align out the different collector capacitance (do one stage at a time).

If you have extreme manual dexterity and bloody good eyesight you can melt
the solder seal between can & header and put the TO92 inside the TO7 can to
preserve the appearance of originality.
 
On May 20, 11:40 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

**  Might be another dodgy chemical fuse  -  eh ??

....  Phil
Click to expand...


Fuses, chemical or not, don't become intermittent.


Idiot.


John
 
"John-Del"
"Phil Allison"

** Might be another dodgy chemical fuse - eh ??
Click to expand...
Fuses, chemical or not, don't become intermittent.


** Then you have not seen everything.

Imbecile.


.... Phil
 
klem kedidelhopper wrote:
On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com...



I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try

Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage that
doesn't really help me to track this down. I could look at the CW
signal from the 249 with my 50MHZ. scope or my spectrum analyzer but I
still don't know what a safe signal amplitude would be. Does anyone
know what the proper typical amplitude of an IF signal would be so
that I would be able to simulate this and inject this signal into the
IF amplifiers and detector stage? BTW except for the outputs, they're
all 4 pin GE transistors. What do you mean by the "simple fudge"?
Thanks, Lenny
Click to expand...

Check the collector voltages on the IF and mixer stage. Use at least
a 1 meg resistor between the probe and the transistor to keep from
disturbing the circuit. I saw a lot of this in old germanium transistor
car radios. Noise induced into the circuit would momentarily restore
the transistor enough to work for a while, but of there was zero
collector voltage, one of the IF transformers was open. If it was high,
the transistor was bad. I troubleshot those radios and repaired most of
them in under five minutes with that simple method. :)


--
It's easy to think outside the box, when you have a cutting torch.
 
klem kedidelhopper wrote:
On May 21, 8:58 pm, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
klem kedidelhopper wrote:

On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com...

I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try

Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage that
doesn't really help me to track this down. I could look at the CW
signal from the 249 with my 50MHZ. scope or my spectrum analyzer but I
still don't know what a safe signal amplitude would be. Does anyone
know what the proper typical amplitude of an IF signal would be so
that I would be able to simulate this and inject this signal into the
IF amplifiers and detector stage? BTW except for the outputs, they're
all 4 pin GE transistors. What do you mean by the "simple fudge"?
Thanks, Lenny

Check the collector voltages on the IF and mixer stage. Use at least
a 1 meg resistor between the probe and the transistor to keep from
disturbing the circuit. I saw a lot of this in old germanium transistor
car radios. Noise induced into the circuit would momentarily restore
the transistor enough to work for a while, but of there was zero
collector voltage, one of the IF transformers was open. If it was high,
the transistor was bad. I troubleshot those radios and repaired most of
them in under five minutes with that simple method. :)

The IF's are AF124,and 126. And to answer a previous question I did
use cold spray on everything but the detector, which is inside a can.
Click to expand...

I may still have a couple new ECG160 in stock. I'll try to get into
the old shop and check, if I can climb through some of the junk that's
piled up to be hauled off.


http://www.nteinc.com/specs/100to199/pdf/nte160.pdf is the datasheet
for the NTE version.


I only used freeze mist as a last resort. On early transistor
equipment it seemed to cause more failures. Thermal expansion & cooling
inside the transistor case caused metal fatigue.


It didn't seem to have any effect. I plan to open the can and hit the
detector too.
Click to expand...

AM or FM? A bad diode shouldn't affect both bands.


The "whiskering" as well as the method to remove it are
both kind of interesting, sort of like what happens to nicads it
seems. Well the transistors seem to have lasted forty some odd years
so I can't complain much. The NTE 160 is a germanium and it seems to
replace all of these however it does not have a fourth can lead.
Click to expand...
A short between the shel & the collector was a common failure.

I don't know if that could make much of a difference. To check one of
these for whiskering, would you simply look for leakage between any
junction and the can? I never thought of this.
Click to expand...
Using an analog meter would caue open juctions to start working
again, for a short time. All this did was make you waste time, since
they invariably quit again. You probably have a crack weld inside the
can, or a fractured bonding wire. That is why I monitored the collector
voltages, with added isolation and used a VTVM, and later, a FETVM.

On another note, considering the bias issues, I really would not want
to use a silicon transistor if I don't have to.
Click to expand...

It's not that difficult to change. If it uses the typical two
resisotor bias, you need to raise the E_B voltage to get .6 volts
instead of .1 volts. Since the silicon parts have less leakage
currents, raise the value of the bottom resistor in the string. Tack a
trimpot or use a resistors sub box to find the new value, and solder it
in.


--
It's easy to think outside the box, when you have a cutting torch.
 
On May 21, 8:58 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
klem kedidelhopper wrote:

On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com....

I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently.  Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand?  Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try

Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage that
doesn't really help me to track this down. I could look at the CW
signal from the 249 with my 50MHZ. scope or my spectrum analyzer but I
still don't know what a safe signal amplitude would be. Does anyone
know what the proper typical amplitude of an IF signal would be so
that I would be able to simulate this and inject this signal into the
IF amplifiers and detector stage? BTW except for the outputs, they're
all 4 pin GE transistors. What do you mean by the "simple fudge"?
Thanks, Lenny

  Check the collector voltages on the IF and mixer stage.  Use at least
a 1 meg resistor between the probe and the transistor to keep from
disturbing the circuit.  I saw a lot of this in old germanium transistor
car radios.  Noise induced into the circuit would momentarily restore
the transistor enough to work for a while, but of there was zero
collector voltage, one of the IF transformers was open.  If it was high,
the transistor was bad.  I troubleshot those radios and repaired most of
them in under five minutes with that simple method. :)

--
It's easy to think outside the box, when you have a cutting torch.
Click to expand...
The IF's are AF124,and 126. And to answer a previous question I did
use cold spray on everything but the detector, which is inside a can.
It didn't seem to have any effect. I plan to open the can and hit the
detector too. The "whiskering" as well as the method to remove it are
both kind of interesting, sort of like what happens to nicads it
seems. Well the transistors seem to have lasted forty some odd years
so I can't complain much. The NTE 160 is a germanium and it seems to
replace all of these however it does not have a fourth can lead. I
don't know if that could make much of a difference.To check one of
these for whiskering, would you simply look for leakage between any
junction and the can? I never thought of this. On another note,
considering the bias issues, I really would not want to use a silicon
transistor if I don't have to. Lenny
 
On May 22, 12:38 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
klem kedidelhopper wrote:

On May 21, 8:58 pm, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
klem kedidelhopper wrote:

On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups..com...

I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently.  Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand?  Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple fudge
is worth a try

Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage that
doesn't really help me to track this down. I could look at the CW
signal from the 249 with my 50MHZ. scope or my spectrum analyzer but I
still don't know what a safe signal amplitude would be. Does anyone
know what the proper typical amplitude of an IF signal would be so
that I would be able to simulate this and inject this signal into the
IF amplifiers and detector stage? BTW except for the outputs, they're
all 4 pin GE transistors. What do you mean by the "simple fudge"?
Thanks, Lenny

  Check the collector voltages on the IF and mixer stage.  Use at least
a 1 meg resistor between the probe and the transistor to keep from
disturbing the circuit.  I saw a lot of this in old germanium transistor
car radios.  Noise induced into the circuit would momentarily restore
the transistor enough to work for a while, but of there was zero
collector voltage, one of the IF transformers was open.  If it was high,
the transistor was bad.  I troubleshot those radios and repaired most of
them in under five minutes with that simple method. :)

The IF's are AF124,and 126. And to answer a previous question I did
use cold spray on everything but the detector, which is inside a can.

   I may still have a couple new ECG160 in stock.  I'll try to get into
the old shop and check, if I can climb through some of the junk that's
piled up to be hauled off.

   http://www.nteinc.com/specs/100to199/pdf/nte160.pdfis the datasheet
for the NTE version.

   I only used freeze mist as a last resort.  On early transistor
equipment it seemed to cause more failures.  Thermal expansion & cooling
inside the transistor case caused metal fatigue.

It didn't seem to have any effect. I plan to open the can and hit the
detector too.

   AM or FM?  A bad diode shouldn't affect both bands.

The "whiskering" as well as the method to remove it are
both kind of interesting, sort of like what happens to nicads it
seems. Well the transistors seem to have lasted forty some odd years
so I can't complain much. The NTE 160 is a germanium and it seems to
replace all of these however it does not have a fourth can lead.

   A short between the shel & the collector was a common failure.

I don't know if that could make much of a difference. To check one of
these for whiskering, would you simply look for leakage between any
junction and the can? I never thought of this.

   Using an analog meter would caue open juctions to start working
again, for a short time.  All this did was make you waste time, since
they invariably quit again.  You probably have a crack weld inside the
can, or a fractured bonding wire.  That is why I monitored the collector
voltages, with added isolation and used a VTVM, and later, a FETVM.

On another note, considering the bias issues, I really would not want
to use a silicon transistor if I don't have to.

   It's not that difficult to change.  If it uses the typical two
resisotor bias, you need to raise the E_B voltage to get .6 volts
instead of .1 volts.  Since the silicon parts have less leakage
currents, raise the value of the bottom resistor in the string.  Tack a
trimpot or use a resistors sub box to find the new value, and solder it
in.

--
It's easy to think outside the box, when you have a cutting torch.
Click to expand...
Good idea about the VTVM. I don't get to use my RCA Senior Voltohmyst
much anymore. I bought it as a kit from the RCA distributor at the
time, Bruno NY in Manhattan and built it when I was 17. It still works
great. I use an Energiser for the ohmmeter but I really do worry about
the battery leaking. I've been meaning to replace the battery with a
little isolated DC supply for a long time but just have never gotten
to it. Lenny
 
"klem kedidelhopper" <captainvideo462009@gmail.com> wrote in message
news:f84e7e90-e7e4-470c-bd7c-cc56751a1013@w36g2000vbi.googlegroups.com...
On May 21, 8:58 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
klem kedidelhopper wrote:

On May 21, 10:05 am, "N_Cook" <dive...@tcp.co.uk> wrote:
klem kedidelhopper <captainvideo462...@gmail.com> wrote in message

news:d384fa64-4fcf-42c3-b061-1c0a786f3c15@p23g2000vbl.googlegroups.com...

I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems
with
it until just recently. Last month I spent three days in the
hospital
and I brought the Grundig with me. I noticed that after it was on
for
about a half hour it would start to cut out. I turned it off and
then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was
wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up
with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of
the
MFJ is and I would hate to blow up an otherwise good IF amplifier
with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? Thanks very much for any advice. Lenny

Any 4 pin Ge transistors in there? if there is then the usual simple
fudge
is worth a try

Well the AM is not working either when this set fails. And since the
set uses the same transistors but different coils for each stage that
doesn't really help me to track this down. I could look at the CW
signal from the 249 with my 50MHZ. scope or my spectrum analyzer but I
still don't know what a safe signal amplitude would be. Does anyone
know what the proper typical amplitude of an IF signal would be so
that I would be able to simulate this and inject this signal into the
IF amplifiers and detector stage? BTW except for the outputs, they're
all 4 pin GE transistors. What do you mean by the "simple fudge"?
Thanks, Lenny

Check the collector voltages on the IF and mixer stage. Use at least
a 1 meg resistor between the probe and the transistor to keep from
disturbing the circuit. I saw a lot of this in old germanium transistor
car radios. Noise induced into the circuit would momentarily restore
the transistor enough to work for a while, but of there was zero
collector voltage, one of the IF transformers was open. If it was high,
the transistor was bad. I troubleshot those radios and repaired most of
them in under five minutes with that simple method. :)

--
It's easy to think outside the box, when you have a cutting torch.
Click to expand...
The IF's are AF124,and 126. And to answer a previous question I did
use cold spray on everything but the detector, which is inside a can.
It didn't seem to have any effect. I plan to open the can and hit the
detector too. The "whiskering" as well as the method to remove it are
both kind of interesting,

===========================================

So far I've never heard of whiskering problems with the AF12x series -
that's not to say it never happens though.

As the fault is intermittent, continuity checks may not tell you anything
useful.

Simply remove the solder from the copper pad around the screen lead and make
sure its isolated, if there is whiskering that will cure the symptom.
 
"Ron D."
I've seen an intermittant 2AG fuse twice, Drove me nuts the first
time. By intermittant, I mean it would open in circuit, but would
test OK with an ohmmeter.
Click to expand...
** Yep.

Typically, the fuse wire has come loose at one end - or was never soldered
in the first place.

It looks fine and has continuity due to light pressure contact alone.

When the wire heats under load, it opens and closes.




...... Phil
 
Phil:

I've seen an intermittant 2AG fuse twice, Drove me nuts the first
time. By intermittant, I mean it would open in circuit, but would
test OK with an ohmmeter.
 
On May 22, 8:42 pm, "Ron D." <ron.doz...@gmail.com> wrote:
Phil:

I've seen an intermittant 2AG fuse twice,  Drove me nuts the first
time.  By intermittant, I mean it would open in circuit, but would
test OK with an ohmmeter.
Click to expand...

I mean 3AG fuse.
 
On Fri, 20 May 2011 15:21:01 -0700, klem kedidelhopper wrote:

I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with it
until just recently. Last month I spent three days in the hospital and
I brought the Grundig with me. I noticed that after it was on for about
a half hour it would start to cut out. I turned it off and then later
turned it on again, and after a period of time it happened again. After
several similar episodes I stopped using it. I wondered about some type
of interference from the hospital but that was wishful thinking. In any
case being in no position to test it I decided to just put it away.
Yesterday I put it on the bench and took a look at it. Sure enough after
a brief time it cut out again. I injected a signal, (my finger on a
small screwdriver) onto the wiper of the volume control and ascertained
that there is nothing wrong up to the speaker. So now I need to get into
the IF's and detector. My problem is my old signal generators are not
working and all I can come up with for 10.7MHZ. is a CW signal out of my
MFJ249 SWR meter. The MFJ puts out a clean signal however it is CW, and
it's amplitude is not adjustable. I don't think that an unmodulated
signal would be a problem in this application but I don't know what the
amplitude of the MFJ is and I would hate to blow up an otherwise good IF
amplifier with an excessive signal. I''m admittedly a bit rusty having
not trouble shot an IF amplifier/detector circuit in many years so does
anyone have a feel for how I might signal trace this radio with what I
have on hand? Thanks very much for any advice. Lenny
Click to expand...
Start with the first RF amp. It's probably a superhet so there will be a
455 osc and mixer. After that a couple rf amps and the the detector.

Google a superhetrodyne receiver. This one uses ICs but the basics are the
same

http://www.seekic.com/uploadfile/ic-circuit/20097173226815.gif

Should give you some insight as to where the signal is being lost in the
path.

--
Live Fast Die Young, Leave A Pretty Corpse
 
"spamtrap1888"
http://www.seekic.com/uploadfile/ic-circuit/20097173226815.gif
Click to expand...
How do you tune the radio in that schematic?


** Like any receiver that uses a crystal oscillator.

By swapping the crystal.

Ask anyone with a RC model.



...... Phil
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top