Toshiba TV29C90 problem; Image fades to black...

On 1 May, 10:33, Robert Inder <rob...@deadspam.com> wrote:

I'm trying to repair an angle poise desk lamp. The actual bulb holder
has broken.

Inside the shade there is a metal bracket, with a roughly 1cm hole
in it. On the original lamp holder, the wires entered through a
threaded "tail" which pushed through this hole. Then there was a nut
that came down the wires and tightened onto the tail of the lamp
holder, thus clamping it to the bracket.

Unfortunately, it looks like the compact fluorescent bulb we've been
using has been too heavy for arrangement, and the threaded "tail" of
the lampholder has broken, leaving the bulb resting against the inside
of the metal shade. It works, but...

So, I'd like to get a replacement lamp holder. One that can holds a
normal 240V bulb, but can be clamped by its tail in to a 1cm mounting hole.

Only I'm not sure where to get such a thing, or even what I want to
ASK for --- what such a thing would be called.

I've seen "batten mounting" lamp holders, and the ones that I've seen
for pendant lights seem to be designed to clamp to a shade or similar
at the middle of the lampholder --- where the body is several
cemtimeters across.

Help?

Robert.

usually its the forces generated when the nut's tightened that breaks
them, not the bulbs. Unfortunately I cant remember what that holder
arrangement is called, but if you call your local electrical
wholesaler they should have one. The new one will be no more robust of
course - go easy on tightening that nut.


NT

 

[James Sweet]

Robert Inder wrote:

I'm trying to repair an angle poise desk lamp. The actual bulb holder
has broken.

Inside the shade there is a metal bracket, with a roughly 1cm hole
in it. On the original lamp holder, the wires entered through a
threaded "tail" which pushed through this hole. Then there was a nut
that came down the wires and tightened onto the tail of the lamp
holder, thus clamping it to the bracket.

Unfortunately, it looks like the compact fluorescent bulb we've been
using has been too heavy for arrangement, and the threaded "tail" of
the lampholder has broken, leaving the bulb resting against the inside
of the metal shade. It works, but...

So, I'd like to get a replacement lamp holder. One that can holds a
normal 240V bulb, but can be clamped by its tail in to a 1cm mounting hole.

Only I'm not sure where to get such a thing, or even what I want to
ASK for --- what such a thing would be called.

I've seen "batten mounting" lamp holders, and the ones that I've seen
for pendant lights seem to be designed to clamp to a shade or similar
at the middle of the lampholder --- where the body is several
cemtimeters across.

Help?

Don't you have a hardware store nearby? Just take the old socket out and
bring it down to a place that sells electrical hardware, they might have
something you can make fit.

 

[Tim]

In article <daOZh.7290$Hd1.1780@trndny07>, jamessweet@hotmail.com
says...

Robert Inder wrote:
I'm trying to repair an angle poise desk lamp. The actual bulb holder
has broken.

Inside the shade there is a metal bracket, with a roughly 1cm hole
in it. On the original lamp holder, the wires entered through a
threaded "tail" which pushed through this hole. Then there was a nut
that came down the wires and tightened onto the tail of the lamp
holder, thus clamping it to the bracket.

Unfortunately, it looks like the compact fluorescent bulb we've been
using has been too heavy for arrangement, and the threaded "tail" of
the lampholder has broken, leaving the bulb resting against the inside
of the metal shade. It works, but...

So, I'd like to get a replacement lamp holder. One that can holds a
normal 240V bulb, but can be clamped by its tail in to a 1cm mounting hole.

Only I'm not sure where to get such a thing, or even what I want to
ASK for --- what such a thing would be called.

I've seen "batten mounting" lamp holders, and the ones that I've seen
for pendant lights seem to be designed to clamp to a shade or similar
at the middle of the lampholder --- where the body is several
cemtimeters across.

Help?



Don't you have a hardware store nearby? Just take the old socket out and
bring it down to a place that sells electrical hardware, they might have
something you can make fit.

Yup, and I would add that it sounds like a standard piece of hardware

used in lamps worldwide. I just call it threaded pipe.

- Tim -

 

[Franc Zabkar]

On Tue, 01 May 2007 05:54:28 -0400, JW <none@dev.nul> put finger to
keyboard and composed:

Hello all, I'm looking for recommendations for debugging test equipment
through their GPIB interface.

Make your own serial to GPIB converter?
http://home8.inet.tele.dk/jan_p/micro/micro1.htm

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[René]

On Tue, 01 May 2007 16:42:59 GMT, "Dave" <dspear99ca@yahoo.delete.com>
wrote:

I seem to have transformed a infrequent mild annoyance into a show-stopper.

Had the exact same problem once in a mixing panel (unbalanced audio,
one channel fading away and coming back, incidental cracle and pop
sounds - cleaning did not help)

turned out to be a leaky electrolyte. Found it by measuring biasses on
every transistor in sight. Tapping the cap did not reveal anything
though.

--
- René

 

[Dave]

<meow2222@care2.com> wrote in message
news:1178053957.612635.81360@n76g2000hsh.googlegroups.com...

On 1 May, 18:49, "Dave" <dspear9...@yahoo.delete.com> wrote:

The still bad switch probably needs disassembling & reassembling, or
else replacing the individual switch or switch block. Rows of
pushbutton things on PCBs were a standard design around for many years
in the 70s & 80s, so finding a replacement from some scrap item is
likely.

I re-cleaned the volume pot with some lubricating cleaner and dried it out
with a hair dryer (on low heat setting). The crackling in the right channel
has now all but disappeared.

The left channel, however, will now work for about 10-30 seconds when the
amp is first powered up, then distorts rapidly over about 1-3 seconds and
cuts out completely after that.

The amp is set up as follows:

Input jacks --> input selector PCB --> volume knob/loudness PCB --> tone
control PCB --> power amp PCB.

I'm going to take out the input caps off the tone control and route the
signal directly from the volume knob to the power amp. That will at least
tell me if the problem is with the preamp or power amp. I'm pretty sure
it's going to be in the power amp, as the second-to-last component in the
pre-amp (tone control board) is the stereo/reverse stereo/mono switch. If
the problem was in the preamp prior to this point, changing this switch
should move the problem from one speaker to the other. Which it does not.
The only downstream component from the stereo/reverse stereo/mono switch is
the balance pot.

When I replaced the caps on the power amp, I cleaned the board with spray
cleaner. It was filthy, like 30 years of dust and grime. In retrospect, I
probably shouldn't have bothered, maybe the cold temperature of the spray
cracked off an internal lead in one of the transisotrs or something.

The last component in the amp is "speaker protector". This is a white
rectangular box about 1-1/4"L x 3/16"W x 1/2"H (approx, I'm not looking at
it right now.). I don't know how this works, but could it possibly be my
problem? Or should I be thinking transistors? I guess if I've got the
whole amp apart it wouldn't be such a big deal to measure bias currents on
both channels at idle... there are 14 transistors per channel including the
outputs.

Re the off balance, there are reasons amps have balance controls. If
yours has none you can fit a potential divider in the channel with the
higher output, and set it up and replace the covers. If youre lcky and
the amp has external connections between pre and power sections, you
can put what you want between those 2, such as a new volume & balance
control.

My amp is integrated, but fortunately is very simple to split as the
connection between pre-amp and amp is a three-conductor wire. I've been
meaning to do this for awhile, I've just purchased a sub with line inputs
and outputs... will have to cannibalize some piece of junk for a block of
RCA jacks.

All of my signal path connections are wire-wound, not soldered. Is there
some tool to do this if I wanted to stay true to design and wind the
connections on my pre-out/main-in connections? Is there any benefit to
doing it this way? I'm guessing there probably is as it looks like a fair
bit more work than just plonking a blob of solder on a ribbon cable lead.

Thanks for the help.

Dave

NT

 

[Joerg Hau]

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).

In my home "lab", I'm using such a setup on a P-II (recently replaced by a
P-III, whew!) for several years now, and it has all the functionality that
I need to read out several DMMs, control a power supply, etc.

Cheers + HTH,

- Joerg


--
joerg dot hau at swissonline dot ch * Lausanne, Switzerland
http://homepage.sunrise.ch/mysunrise/joerg.hau/
"All standard disclaimers apply".
remove the obvious from my address to reply

 

[pfjw@aol.com]

On May 1, 12:42 pm, "Dave" <dspear9...@yahoo.delete.com> wrote:

I have a mid-80's HK integrated amp (PM-650). It's been very reliable

<snip>

Any replies greatly appreciated.

In no particular order:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.

Good luck with it.

Peter Wieck
Wyncote, PA

 

[Dave]

<pfjw@aol.com> wrote in message
news:1178141401.764048.27780@c35g2000hsg.googlegroups.com...

On May 1, 12:42 pm, "Dave" <dspear9...@yahoo.delete.com> wrote:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.

I re-cleaned with a cleaner with lubricant last night.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

Did not re-do switches. I will though.

c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...

I don't have an ESR meter. Is testing plain ol' capacitance any help? I'd
like to think it's a capacitor given that that's all I changed out.

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.

This was an overnight change, so unless the change was mechanically induced
(definitely not ruling that out) I wouldn't be inclined to look there
justyet.

The more I think about it the less likely a pre-amp problem seems... the
signal goes through primary amplification (a few transisitors) then through
tone controls, subsonic filter, high cut filter, balance control --> power
amp. I've got a switch to bypass the tone control, and switches to bypass
the filters, plus a switch to reverse the channels between pre-amp and amp.
None of these affect the amp output. If I've got a bad cap in the amp
stages and am getting a DC offset at my outputs, that MAY be engaging the
speaker protection. Or, I suppose, worst case scenario I've baked one of my
giant expensive output transistors. I am assuming the speaker protection
(being two leaded) is a polyswitch. The distorted sound for a second or so
prior to speaker cut-out might match a polyswitch tripping, I don't know as
I've only ever had amps with relay protection (or none) in the past. Do you
know offhand if polyswitches tend to fail? I suppose probably as much as
any other component exposed to variable voltage and current.

I'm going to bypass the preamp section. If I can confirm that the problem
is in the amp, I could a) check DC voltages at all transistors until I find
one that's off or b) start swapping electrolytic capacitors from channel to
channel. there are only four per channel in the amp section.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.

Yes I've had several of those; they can try your patience.

Good luck with it.

Thanks, I may just need it.

Peter Wieck
Wyncote, PA

 

[Paul Dwerryhouse]

imorf <imorf@iformRemovethis.com.au> writes:

If I was digg, I'd have put up a content warning then permanently banned
every account that posted a story deliberately about it.

What point is that when people can sign up again under a different name?

Digg needs its users to survive. The users can desert them for any number of
similar news sites that would be more than happy to accept them. And the users
made that point very effectively, yesterday.

--
Paul Dwerryhouse | PGP Key ID: 0x6B91B584

 

[Dr. Anton T. Squeegee]

In article <MPG.20a3adee6c1d3f998a898@News.Individual.net>,
fishcakes@tanksville.com (known to some as fish.) scribed...

In article <1178120327.445089.269560@y80g2000hsf.googlegroups.com>,
fr_tamr@yahoo.com says...
HD-DVD key has been cracked. Get the hex here:
http://www.speedateauction.com/blog/blog_detail.asp?blog_id=1354&user_id=100915

I have never seen a hex so beautiful as this.




And I've never seen such a pack of dopey retards crapping on about stuff
they know fuck all about.

If you had any fucking clue what to do with it, you'd realise that
BackupHDVD was using it so long ago that it's already been revoked.

If it's so useless, then why is the group responsible for designing
the content "protection" keys getting all hyper about issuing DMCA-based
takedown notices to everyone under the sun?

I would also point out that it has spread like wildfire on the 'net
itself, in one of the most magnificent cases of electronic civil
disobedience since DeCSS. Any wagers as to how long it'll be before the
T-shirts appear? ;-)

Keep the peace(es).


--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
http://www.bluefeathertech.com -- kyrrin a/t bluefeathertech d-o=t calm
"Salvadore Dali's computer has surreal ports..."

 

[Mark D. Zacharias]

Dave wrote:

meow2222@care2.com> wrote in message
news:1178053957.612635.81360@n76g2000hsh.googlegroups.com...
On 1 May, 18:49, "Dave" <dspear9...@yahoo.delete.com> wrote:

The still bad switch probably needs disassembling & reassembling, or
else replacing the individual switch or switch block. Rows of
pushbutton things on PCBs were a standard design around for many
years in the 70s & 80s, so finding a replacement from some scrap
item is likely.


I re-cleaned the volume pot with some lubricating cleaner and dried
it out with a hair dryer (on low heat setting). The crackling in the
right channel has now all but disappeared.

The left channel, however, will now work for about 10-30 seconds when
the amp is first powered up, then distorts rapidly over about 1-3
seconds and cuts out completely after that.

The amp is set up as follows:

Input jacks --> input selector PCB --> volume knob/loudness PCB --
tone control PCB --> power amp PCB.

I'm going to take out the input caps off the tone control and route
the signal directly from the volume knob to the power amp. That will
at least tell me if the problem is with the preamp or power amp. I'm
pretty sure it's going to be in the power amp, as the second-to-last
component in the pre-amp (tone control board) is the stereo/reverse
stereo/mono switch. If the problem was in the preamp prior to this
point, changing this switch should move the problem from one speaker
to the other. Which it does not. The only downstream component from
the stereo/reverse stereo/mono switch is the balance pot.

When I replaced the caps on the power amp, I cleaned the board with
spray cleaner. It was filthy, like 30 years of dust and grime. In
retrospect, I probably shouldn't have bothered, maybe the cold
temperature of the spray cracked off an internal lead in one of the
transisotrs or something.
The last component in the amp is "speaker protector". This is a white
rectangular box about 1-1/4"L x 3/16"W x 1/2"H (approx, I'm not
looking at it right now.). I don't know how this works, but could it
possibly be my problem? Or should I be thinking transistors? I
guess if I've got the whole amp apart it wouldn't be such a big deal
to measure bias currents on both channels at idle... there are 14
transistors per channel including the outputs.


Re the off balance, there are reasons amps have balance controls. If
yours has none you can fit a potential divider in the channel with
the higher output, and set it up and replace the covers. If youre
lcky and the amp has external connections between pre and power
sections, you can put what you want between those 2, such as a new
volume & balance control.

My amp is integrated, but fortunately is very simple to split as the
connection between pre-amp and amp is a three-conductor wire. I've
been meaning to do this for awhile, I've just purchased a sub with
line inputs and outputs... will have to cannibalize some piece of
junk for a block of RCA jacks.

All of my signal path connections are wire-wound, not soldered. Is
there some tool to do this if I wanted to stay true to design and
wind the connections on my pre-out/main-in connections? Is there any
benefit to doing it this way? I'm guessing there probably is as it
looks like a fair bit more work than just plonking a blob of solder
on a ribbon cable lead.
Thanks for the help.

Dave



NT

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.


Mark Z.

 

[Dave]

"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

 

[pfjw@aol.com]

On May 3, 10:38 am, "Dave" <dspear9...@yahoo.delete.com> wrote:

"Mark D. Zacharias" <spamme...@nonsense.net> wrote in messagenews: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- Hide quoted text -

- Show quoted text -

Do you have a good transistor checker? (one that does good/bad and is
also capable of matching?)

Where are you (by region)?

Peter Wieck
Wyncote, PA

 

[Dave]

<pfjw@aol.com> wrote in message
news:1178216438.079497.170180@y80g2000hsf.googlegroups.com...

On May 3, 10:38 am, "Dave" <dspear9...@yahoo.delete.com> wrote:

Do you have a good transistor checker? (one that does good/bad and is
also capable of matching?)

Where are you (by region)?

Peter Wieck
Wyncote, PA

I've got a transistor checker on my multimeter, it shows an arbitrary hfe

which, for a given transistor, never matches what's in the data sheet. Of
course the gain in the datasheet is always at a particular voltage and
current and I'm not sure what voltages/currents are applied by the meter...
or whether the voltage or current is controlled at all. I'm guessing 9V at
whatever the multimeter battery can put out for current through an unknown
series resistor. If it's a truly fried transistor, no value is returned for
hfe. I've had as much luck testing transistors with an ohmmeter.

I've never really trusted it to be honest with you.

Are you thinking driver transistor? Maybe one early in the signal path
which could introduce DC voltage which carries right through and would
explain the elevated voltages I am seeing in the left channel?

I live in Penticton, British Columbia, Canada. It's about 250 miles inland
from Vancouver and about 40 miles from the Washington border. It's a town
of 30,000 and, as you may surmise, very little of my equipment and parts is
purchased locally.

Dave

 

[pfjw@aol.com]

On May 3, 2:32 pm, "Dave" <dspear9...@yahoo.delete.com> wrote:

p...@aol.com> wrote in message

news:1178216438.079497.170180@y80g2000hsf.googlegroups.com...> On May 3, 10:38 am, "Dave" <dspear9...@yahoo.delete.com> wrote:

Do you have a good transistor checker? (one that does good/bad and is
also capable of matching?)

Where are you (by region)?

Peter Wieck
Wyncote, PA

I've got a transistor checker on my multimeter, it shows an arbitrary hfe
which, for a given transistor, never matches what's in the data sheet. Of
course the gain in the datasheet is always at a particular voltage and
current and I'm not sure what voltages/currents are applied by the meter...
or whether the voltage or current is controlled at all. I'm guessing 9V at
whatever the multimeter battery can put out for current through an unknown
series resistor. If it's a truly fried transistor, no value is returned for
hfe. I've had as much luck testing transistors with an ohmmeter.

I've never really trusted it to be honest with you.

Are you thinking driver transistor? Maybe one early in the signal path
which could introduce DC voltage which carries right through and would
explain the elevated voltages I am seeing in the left channel?

I live in Penticton, British Columbia, Canada. It's about 250 miles inland
from Vancouver and about 40 miles from the Washington border. It's a town
of 30,000 and, as you may surmise, very little of my equipment and parts is
purchased locally.

Dave

Exactly on the driver transistor. And "by region" I was thinking if
you were relatively nearby I would send you my transistor checker to
help through this process. Canada may be squirrelly what with customs
and such, by the time it reached you, you would have found the
problem. Then you would have to send it back.

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.

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

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

Peter Wieck
Wyncote, PA

 

[Dave]

<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

 

[pfjw@aol.com]

On May 3, 3:20 pm, "Dave" <dspear9...@yahoo.delete.com> wrote:

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

Exactly.

And why I try to get a bit closer than a cross-reference when I use
even direct-replacements. Unlike tubes which can vary somewhat,
transistors can vary pretty vastly, well beyond what common sense
suggests. And even though transistors do not really have a "burn-in",
when they begin to fail they can drift for a brief period before final
failure sets in.

Peter Wieck
Wyncote, PA

 

[Mr. Land]

On May 2, 6:39 pm, "Dave" <dspear9...@yahoo.delete.com> wrote:

p...@aol.com> wrote in message

news:1178141401.764048.27780@c35g2000hsg.googlegroups.com...

On May 1, 12:42 pm, "Dave" <dspear9...@yahoo.delete.com> wrote:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.

I re-cleaned with a cleaner with lubricant last night.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

Did not re-do switches. I will though.



c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...

I don't have an ESR meter. Is testing plain ol' capacitance any help? I'd
like to think it's a capacitor given that that's all I changed out.

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.

This was an overnight change, so unless the change was mechanically induced
(definitely not ruling that out) I wouldn't be inclined to look there
justyet.

The more I think about it the less likely a pre-amp problem seems... the
signal goes through primary amplification (a few transisitors) then through
tone controls, subsonic filter, high cut filter, balance control --> power
amp. I've got a switch to bypass the tone control, and switches to bypass
the filters, plus a switch to reverse the channels between pre-amp and amp.
None of these affect the amp output. If I've got a bad cap in the amp
stages and am getting a DC offset at my outputs, that MAY be engaging the
speaker protection. Or, I suppose, worst case scenario I've baked one of my
giant expensive output transistors. I am assuming the speaker protection
(being two leaded) is a polyswitch. The distorted sound for a second or so
prior to speaker cut-out might match a polyswitch tripping, I don't know as
I've only ever had amps with relay protection (or none) in the past. Do you
know offhand if polyswitches tend to fail? I suppose probably as much as
any other component exposed to variable voltage and current.

I'm going to bypass the preamp section. If I can confirm that the problem
is in the amp, I could a) check DC voltages at all transistors until I find
one that's off or b) start swapping electrolytic capacitors from channel to
channel. there are only four per channel in the amp section.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.

Yes I've had several of those; they can try your patience.

Good luck with it.

Thanks, I may just need it.

Peter Wieck
Wyncote, PA

There used to be a spray on the market - can't remember who made it at
the time, might have been GC - it was called "Blue Stuff". I worked
in a stereo service department thru college, and that spray was the
best we could find for cleaning stubbornly noisy pots and switches.
When you sprayed it on it formed a mildly abrasive blue paste, which
would actually scrub the tarnish and dirt off of switch contacts. I
never saw it fail, even with the noisiest, most tarnished switches and
controls. I think it has diatomaceous earth in it.

Anyway, I think TechSpray carries it - might be worth a try
(www.techspray.com)

 

[JW]

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.