Toshiba TV29C90 problem; Image fades to black...

[Dave]

<pfjw@aol.com> wrote in message
news:1178217891.816907.8870@c35g2000hsg.googlegroups.com...

http://cgi.ebay.com/Schlumberger-Heathkit-Model-IT-18-Transistor-Tester_W0QQitemZ170108095101

Not as fancy as their IT-30, but it does the trick

I just picked up an IT-27 on eBay for $9. Plus of course the obligatory

$10-15 shipping, I should have it within a week or so.

 

[Mark D. Zacharias]

Dave wrote:

pfjw@aol.com> wrote in message
news:1178217891.816907.8870@c35g2000hsg.googlegroups.com...
I have had very good luck "pairing" transistors when doing repairs/
upgrades for 70s vintage SS amps (Dynaco, Scott, AR, Fisher), that is
making sure the 'right-side' transistor is reasonably closely matched
to the same 'left-side' transistor. This little instrument really
does help.

Thanks for the link. As luck would have it, the seller lives in my
home town of Camden, Maine. Weird.

This tool would be really really handy and it's a helluva' lot
cheaper than a 'scope.

A couple of the driver transistors are not available, 2SC2603 and
2SA949's. NTE crosses would have to do.

Thanks

Dave

Maybe not an issue, but the 2603 and the 949 are not a pair. The C2603 is a
really small signal type, even smaller than a TO-92 package, The A949 is
similar to a TO-92 but taller. Don't know the package designation. I think
it's complement is the 2SC2229. They are readily available. I get them from
Onkyo and B & D Enterprises. BTW if you register on BDent.com you can get
datasheets for these really easily.

I'll try to look over your troubleshooting results with the schem and post
back.


Mark Z.

 

[JW]

On Fri, 04 May 2007 05:47:23 -0400 JW <none@dev.nul> wrote in Message id:
<kttl33hao7t9osd3j7djiqh7lfu2j919rc@4ax.com>:

On Wed, 02 May 2007 22:06:48 +0200 Joerg Hau
nospam.joerg.hau@swissonline.ch> wrote in Message id:
pj7ng4-1k3.ln1@c2.localnet>:

Hi,

Hello all, I'm looking for recommendations for debugging test equipment
through their GPIB interface.
[...]
I currently have no GPIB hardware or software, but have taken a look at
National Instruments who have both a USB and a PCI based GPIB card which
I suppose come with drivers. http://www.ni.com/gpib/ Is this all I need
to get a simple terminal-like interface which will enable me to
communicate with the meter?

Go with the HP card and drivers. Still not cheap for a PCI card. Which
leaves ebay for an older card using the AT interface and maybe DOS or
Win95 and a bit of ingenuity.

Even easier ... apart from Steve's idea with the HP-85, I would suggest to
get some old PC with an ISA slot, plus an ISA-slot GPIB card such as the
HP82335 (which you can get *much* cheaper than any PCI card today).

Install Linux on the PC, install the linux-gpib package, and off you go
If you need some sample code - command line only, no GUI involved - feel
free to have a look at my website (link below).

Thanks, and thanks to everybody who responded, I appreciate your time.
I'll be sure take a look at your stuff. Somebody also emailed me with
regards to this, and mentioned a cheap ($149) Prologix USB adapter
http://prologix.googlepages.com/home and FREE software for Windows
http://www.thegleam.com/ke5fx/gpib/readme.htm As a bonus (for you
programmer types, not me) the source code comes with it.

Thanks again.

As a somewhat unrelated question, A lot of test equipment is built in a
backplane or plug-in type architecture. How the heck to you access the
boards/modules when you need to probe them? I figure that the OEM had
specially made extender cards for their techs; is there any aftermarket
company who sells these things? I had very little luck in finding anything
on this, except for common busses like PCI, ISA, VME, etc.

Thanks again!

 

[Mark D. Zacharias]

Dave wrote:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:QYi_h.4254$H_.3824@newssvr21.news.prodigy.net...

The posts I've seen in this thread do seem to suggest a problem with
coupling caps. Also, I've seen bad (open circuit or intermittent)
polystyrene caps on HK's in the past.

If you're not already using them, a sine/square generator and an
oscilloscope would be most useful here. In addition to rapidly
narrowing down to the affected stage, a square wave might show that
you have a frequency response problem in the affected stage. If so,
the source of the problem may well be more obvious.

Remember that with coupling caps, you can often get a clue with DC
voltages. There may be DC, or a higher DC than the other channel, on
the output side of a bad cap, or the following transistor stage may
show a low collector voltage.

If indeed the static was not controlled by the volume or balance,
then your problem is narrowed down a bit, assuming there is only the
one problem involved here

I have the service manual pdf if you need it.


Thanks Mark, I've got the service manual. I do not currently own a
functioning oscilloscope (two fine doorstops), yes it would certainly
help here. Ah, but these old amps are simple enough to diagnose
without one. Nothing but resistors, caps, and transistors. And time,
lots and lots of time.

The problem is definitely in the amp section. I separated the
pre-amp and amp and tested both. The pre-amp drove an external amp
just fine, the amp exhibited the same symptoms with another preamp.

As there are only four electrolytic caps in each channel of the
amplifier, it's a fairly quick fix to swap them out one at a time
until (hopefully) the amp comes back to life.

I tested the voltages everywhere in the amp on both channels, wherever
voltages were shown in the service manual. The affected (left)
channel had voltages a couple of volts higher ON AVERAGE (2-2.5VDC)
than the corresponding right channel components which were really
close to expected values. I replaced the input coupling cap on the
bad channel which did not help.

Following your advice I looked at collector voltages... there is one
that really stands out and that is Q405. Expected is -7.1V and I
read -0.3V. This collector is tied to the emitters of Q401 and Q403
via a resistor network... the emitter voltages of Q401 and Q403 are
also significantly off (low). It's a tough call when your expected
voltage is less than a volt... Q401 emitter should be -0.6V and I see
-0.2. Q403 should be -0.6 and I see 0. The only cap in the signal path
prior to these transistors is
C401, the input coupling cap which I swapped out as a first try. Otherwise
there's an electrolytic from the negative rail to the base
of Q405... that'll be next.
Thanks for your help.

Dave

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it is
Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case you
need to see that Q405 turns off hard a few seconds after turn-on. The -12.5
or so volts at the base is critical.

Mark Z.

 

[bz]

Joerg Hau <nospam.joerg.hau@swissonline.ch> wrote in
newsj7ng4-1k3.ln1@c2.localnet:

Hi,

Hello all, I'm looking for recommendations for debugging test
equipment through their GPIB interface.
[...]
I currently have no GPIB hardware or software, but have taken a look
at National Instruments who have both a USB and a PCI based GPIB card
which I suppose come with drivers. http://www.ni.com/gpib/ Is this all
I need to get a simple terminal-like interface which will enable me to
communicate with the meter?

.....

Or for a 'more modern approach' a GPIB/USB interface such as
http://www.techsoft.de/htbasic/82357am.htm?82357a.htm






--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[sparky]

On May 8, 8:19 am, basketballboxg...@mail.com wrote:

www.BrandonsMansion.com

SPAM ALERT

 

[Dave]

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
newsm__h.4408$H_.3864@newssvr21.news.prodigy.net...

Dave wrote:
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:QYi_h.4254$H_.3824@newssvr21.news.prodigy.net...


Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it
is Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case
you need to see that Q405 turns off hard a few seconds after turn-on.
The -12.5 or so volts at the base is critical.

Mark Z.

Mark:

First off, thanks very much for all of your insight and time.

Okay, as I had just "upgraded" C405 and C407, I put the originals back.
Left channel is now functional once again, although I haven't had time to
check my voltages yet nor have I given it a good listening test. I can't
say why, but I've got a gut feeling my voltages are still on the high side.
How common is it for zener voltages to wander over three decades?

I set about setting the idle currents and, as soon as I touched V404 (right
channel), poof, right channel gone. I think the 1K pot just disintegrated
when I moved it after 30 years of sitting in one position. Well, I must be
doing something right, because I stumbled across a 1K 70's style (BIG) pot
in one of my many doorstops which I am cannibalizing to make myself an ESR
meter. I'll put it in tonight, hopefully it's in better condition than the
one I'm taking out. One wonders at moments like this whether one is moving
forward or backward...

I can't believe there are so few companies that make ESR meters... the more
I get into electronics repair, the more critical such a piece of equipment
becomes. Ditto with a transistor tester although there seem to be tons of
those on the market.

I have a hard time with transistor theory... I understand what they do, but
get quite confused when I see a whole bunch of them tied together,
controlling each other with various feedback schemes. That's when I start
testing components as I lack the deductive skills required to narrow things
down, as you did, to a single transistor and associated passive components.
Hopefully I'll get better at it... I've read some texts but don't find the
ones I've read particularly helpful. They all seem to assume that one is in
a laboratory environemnt at school with access to and training on the SPICE
program, in particular. Which I do not have.

An oscilloscope and signal generator are handy, but again is somewhat hit or
miss (for me) when I get into a transistor network as it's not immediately
obvious where the signal path is. It's almost easier in a newer amp with
IC's... what you end up doing is replacing an IC with ten transistors in it
because you know the problems's gotta' be in there someplace if you've got
signal going in and none coming out. If the IC is not obsolete and/or
proprietary and hence unavailable. In the past I've used the scope to
localize distortion which saves A LOT of time and lifting of legs to test
components.

I am quickly learning that with vintage audio gear, if it ain't broke, don't
even breathe on it or else...

Thanks again for your help.

Dave

 

[bz]

"Dave" <dspear99ca@yahoo.delete.com> wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in a
newer amp with IC's... what you end up doing is replacing an IC with ten
transistors in it because you know the problems's gotta' be in there
someplace if you've got signal going in and none coming out. If the IC
is not obsolete and/or proprietary and hence unavailable. In the past
I've used the scope to localize distortion which saves A LOT of time and
lifting of legs to test components.

If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a curve
tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad gates on
IC because the 'knee' gets rounded or is absent on bad junctions.

Often, you can test 'in circuit', but sometimes you will have to cut some
traces to isolate the junction from caps or resisitors that are in parallel
with it.

A little practice with one of these, and a few 'reference junctions' to
compare with the curves you see, and you may love your curve tracer too.

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[Michael Kennedy]

Reported to groups-abuse@google.com

 

[Mark D. Zacharias]

bz wrote:

"Dave" <dspear99ca@yahoo.delete.com> wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.

I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might have
given up on being a tech and moved on to something else before I ever "got a
clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky transistor
junction becomes obvious. Open capacitor, no problem. You can even connect
it to a phototransistor and fire a remote at the transistor and observe it
turning on and off on your 'scope screen (though this doesn't tell how well
the device works in-circuit...)


Mark Z.

 

[Dave]

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:9%h0i.1356$LR5.467@newssvr17.news.prodigy.net...

bz wrote:
"Dave" <dspear99ca@yahoo.delete.com> wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might
have given up on being a tech and moved on to something else before I ever
"got a clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky transistor
junction becomes obvious. Open capacitor, no problem. You can even connect
it to a phototransistor and fire a remote at the transistor and observe it
turning on and off on your 'scope screen (though this doesn't tell how
well the device works in-circuit...)


Mark Z.

I must say I am intrigued... sort of an all-in-one tester which costs less

than $5 to make. Doesn't get much better than that. What is the value or
the variable resistor ? 1K? 100K? Or would one use the guess and check
method for an acceptable output on the scope?

Dave

 

[bz]

"Dave" <dspear99ca@yahoo.delete.com> wrote in
news:VZm0i.38249$KN6.1602@edtnps89:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:9%h0i.1356$LR5.467@newssvr17.news.prodigy.net...
bz wrote:
"Dave" <dspear99ca@yahoo.delete.com> wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might
have given up on being a tech and moved on to something else before I
ever "got a clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky
transistor junction becomes obvious. Open capacitor, no problem. You
can even connect it to a phototransistor and fire a remote at the
transistor and observe it turning on and off on your 'scope screen
(though this doesn't tell how well the device works in-circuit...)


Mark Z.

I must say I am intrigued... sort of an all-in-one tester which costs
less than $5 to make. Doesn't get much better than that. What is the
value or the variable resistor ? 1K? 100K? Or would one use the guess
and check method for an acceptable output on the scope?

Yep. You want to have a good horizontal deflection. Depends on the gain on
your horizontal input.

I built my into a wallwart, brought the scope leads for the resistors
directly out through some slits in the case. I just clip the probes from my
scope to the leads.

Glued a diode to the case to use as a reference.

Used a few feet of light duty speaker wire and a couple of E-Z Hook clips
for the circuit board test end.



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[GregS]

In article <VZm0i.38249$KN6.1602@edtnps89>, "Dave" <dspear99ca@yahoo.delete.com> wrote:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:9%h0i.1356$LR5.467@newssvr17.news.prodigy.net...
bz wrote:
"Dave" <dspear99ca@yahoo.delete.com> wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might
have given up on being a tech and moved on to something else before I ever
"got a clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky transistor
junction becomes obvious. Open capacitor, no problem. You can even connect
it to a phototransistor and fire a remote at the transistor and observe it
turning on and off on your 'scope screen (though this doesn't tell how
well the device works in-circuit...)


Mark Z.

I must say I am intrigued... sort of an all-in-one tester which costs less
than $5 to make. Doesn't get much better than that. What is the value or
the variable resistor ? 1K? 100K? Or would one use the guess and check
method for an acceptable output on the scope?

Seems like some cheap scopes came with a component tester. probably about
the same. Reminded me I somehow aquired a commercial unit, so i am looking at it, never used it.
It has a 555 oscillator and some circuitry, but I don'r have a schematic. Can't find
it on the web but will look some more. i should use this usefull tool.

greg

 

[Dave]

"GregS" <szekeres@pitt.edu> wrote in message
news:f1ta1v$96f$1@usenet01.srv.cis.pitt.edu...

In article <VZm0i.38249$KN6.1602@edtnps89>, "Dave"
dspear99ca@yahoo.delete.com> wrote:

Seems like some cheap scopes came with a component tester. probably about
the same. Reminded me I somehow aquired a commercial unit, so i am looking
at it, never used it.
It has a 555 oscillator and some circuitry, but I don'r have a schematic.
Can't find
it on the web but will look some more. i should use this usefull tool.

greg

If the circuit is anything like the one in the link bz posted, it's a few
resistors and a transformer, shouldn't be hard to figure out schematic.

 

Michael Kennedy wrote:

Reported to groups-abuse@google.com

Don't stop there. Paste the IP of his Posting Host into this URL
(already done)
http://www.dnsstuff.com/tools/whois.ch?email=on&ip=66.174.92.164
and report him to his ISP.
mailto:abuse@verizonwireless.com abuse@ verizonwireless.com

 

[Dave]

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
newsm__h.4408$H_.3864@newssvr21.news.prodigy.net...

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it
is Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case
you need to see that Q405 turns off hard a few seconds after turn-on.
The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the original caps

(C401, 403, 405, 407) back in and the problem went away. For awhile. It's
back... I measured voltages after the right channel had cut out.

The collector of Q407 was 0V. So was the collector and base of Q409, and
the base of Q413. Makes sense as they're all tied together. The collector
of Q405 was also 0V. the collectors of Q411 and Q413 were ALSO 0V. I noted
that although R437 tested fine, it looks like it's been run hot. As in it's
dark brown and you can't really read the color bands any more.

I don't understand how Q405 works as far as the turn-on delay, but if it
were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

 

[Mark D. Zacharias]

Dave wrote:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
newsm__h.4408$H_.3864@newssvr21.news.prodigy.net...

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes. On
this model it is Q405 and Q406 respectively. The transistor could be
bad, but I would be especially concerned with D401, R405, C405,
C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in any
case you need to see that Q405 turns off hard a few seconds after
turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the original
caps (C401, 403, 405, 407) back in and the problem went away. For
awhile. It's back... I measured voltages after the right channel
had cut out.
The collector of Q407 was 0V. So was the collector and base of Q409,
and the base of Q413. Makes sense as they're all tied together. The
collector of Q405 was also 0V. the collectors of Q411 and Q413 were
ALSO 0V. I noted that although R437 tested fine, it looks like it's
been run hot. As in it's dark brown and you can't really read the
color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but if
it were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't thinking
clearly before, but the basic principle is the same. As the power supply
comes up, a positive voltage is passed through D401 and D402 to turn ON Q405
and Q406. In the case of Q405, you can see that there should be a negative
voltage at the emitter, and a somewhat LESS negative voltage at the base.
This turns ON the transistor and should pass a negative voltage through the
transistor, so that the negative 7 volts or so appears at the collector. If
there's no voltage at the collector of Q405, it's likely there is no
negative voltage at the emitter either. Possibly R429 or R429 are opening
up, or there could be bad solder connections on one or both of them.

Let me know what you find.

Mark Z.

 

[Dave]

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:8K82i.3600$mR2.2417@newssvr22.news.prodigy.net...

Dave wrote:
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
newsm__h.4408$H_.3864@newssvr21.news.prodigy.net...

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes. On
this model it is Q405 and Q406 respectively. The transistor could be
bad, but I would be especially concerned with D401, R405, C405,
C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in any
case you need to see that Q405 turns off hard a few seconds after
turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the original
caps (C401, 403, 405, 407) back in and the problem went away. For
awhile. It's back... I measured voltages after the right channel
had cut out.
The collector of Q407 was 0V. So was the collector and base of Q409,
and the base of Q413. Makes sense as they're all tied together. The
collector of Q405 was also 0V. the collectors of Q411 and Q413 were
ALSO 0V. I noted that although R437 tested fine, it looks like it's
been run hot. As in it's dark brown and you can't really read the
color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but if
it were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't
thinking clearly before, but the basic principle is the same. As the power
supply comes up, a positive voltage is passed through D401 and D402 to
turn ON Q405 and Q406. In the case of Q405, you can see that there should
be a negative voltage at the emitter, and a somewhat LESS negative voltage
at the base. This turns ON the transistor and should pass a negative
voltage through the transistor, so that the negative 7 volts or so appears
at the collector. If there's no voltage at the collector of Q405, it's
likely there is no negative voltage at the emitter either. Possibly R429
or R429 are opening up, or there could be bad solder connections on one or
both of them.

Let me know what you find.

Oops I guess I omitted information... had typed it then deleted it as

insignificant. I did test the negative power rail at R417 where the schemo
shows -14.2V. It was, I think around -14.9V. In the zone anyways which
would rule out R427 or R429 as culprits. If one of these had opened up
would I not likely see a positive voltage at the base of Q405?

Base Collector Emitter
Q405 -14.2 -0.4 -14.7
Q406 -12.7 -6.9 -13.5

As you can see the base vs. emitter of the two transistors has a comparable
delta... say a half-volt lower at the base which is what you'd expect I
think.

So, if I have the correct voltages at the base and emitter of Q405, but the
wrong collector voltage, I should be looking hard at Q405? I would think
that the -0.4V seen at the collector would be derived from the 2 x -0.6V
coming out of Q401 and Q403 attenuated by R413/R415/R483 with no
contribution from Q405.

Dave

 

[vcdios]

Phil Allison Wrote:

"David L. Jones" tronnort@yahoo.com wrote in message
news:894aa0b3.0307270017.a45cfc4@posting.google.com...
-
I'm after a schematic for the above model scope, any help
appreciated.
-



** I have one for a CS1562 ... if that is any use.



............ Phil

Hi David and Phil

I have one for CS1560A service manual with schematic and parts list.
I am looking for one for CS1562, could you send it to me?

Thanks




--
vcdios

 

[DeserTBoB]

On 15 May 2007 08:19:18 -0700, duty-honor-country
<dutyhonorcountry2@hotmail.com> wrote:

http://i1.tinypic.com/62qy54k.jpg

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USA

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Forward his spam post to:

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groups-abuse@google.com

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You may also want to give Mr. Stola a ring and tell him that
associating with known criminals won't look very good for his failing
business!