Date   

Re: 7934 troubleshooting

JJ
 

I had the power supply ticking problem on my 7904 - eventually, after tracing the problem for weeks changing one tantalum cap after another (didn't even use tantalum for temporary testing), it finally became resurrected! I then replaced the replaced caps. Ticking usually signals first change the caps, one after another, testing for power up after each change. If that doesn't fix it, then you need to get in deeper. You can get fooled easily measuring voltages around the caps. and diodes. Note that I measured the capacitance and leakage of each tantalum cap, using my beautiful Sencore LC75 after removal, and they all were within 1% with strikingly low leakage except for the problem child that was shorted. The caps that Tektronix used were very high quality indeed. Good luck! Seeing it power up will make your heart skip a beat!


Re: SA 492P with probe P6201

Attilio
 

Thank you so much, I proceed to tests.

-- Cheers
Attilio


Re: Type 519 -- Why 125 ohms?

Tom Lee
 

Pretty much everyone on this list has the analysis chops to do it. It's just that everyone has better things to do with their time. So many Netflix series to binge-watch! :)

And your intuition is spot on about those other factors mattering. The numbers you cite come from assuming a coaxial line with air dielectric.  The answers will be different for other geometries, and the introduction of dielectrics makes the answers also depend on frequency. But that's too complicated, so the industry settled on values from the air-dielectric coax calculation. You have to standardize on something.

If anyone gives a rat's patootie about the derivation, please contact me off list and I can send you a couple of pages.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/13/2021 13:33, Jim Ford wrote:
I thought it was about 77 ohms.  75 ohm TV coax being very close.  Maximum power handling supposedly occurs for about 30 ohms, and 50 ohms is a compromise between lowest loss and highest power handling.  I've always thought that there would be variations In both  with dielectric and conductor materials and geometry (e.g. coax, microstrip, coplanar waveguide, etc).  Don't have the analysis chops to calculate it myself....             Jim Ford Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Göran Krusell <mc1648pp@gmail.com> Date: 5/13/21 12:55 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Type 519 -- Why 125 ohms? My memory tells me that the Germans in the 1930s (?) made calculations to figure out if there would be a certain characteristic impedance that would give you the lowest possible cable losses and found 60 ohm as the result. Or am I out in the blue?Göran



Re: Type 519 -- Why 125 ohms?

Jim Ford
 

I thought it was about 77 ohms.  75 ohm TV coax being very close.  Maximum power handling supposedly occurs for about 30 ohms, and 50 ohms is a compromise between lowest loss and highest power handling.  I've always thought that there would be variations In both  with dielectric and conductor materials and geometry (e.g. coax, microstrip, coplanar waveguide, etc).  Don't have the analysis chops to calculate it myself....             Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Göran Krusell <mc1648pp@gmail.com> Date: 5/13/21 12:55 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Type 519 -- Why 125 ohms? My memory tells me that the Germans in the 1930s (?) made calculations to figure out if there would be a certain characteristic impedance that would give you the lowest possible cable losses and found 60 ohm as the result. Or am I out in the blue?Göran


Re: Type 519 -- Why 125 ohms?

Tom Lee
 

(Sorry if this is a duplicate -- my email crashed just after I hit 'send' earlier, and the post had not shown up upon restart)

Close -- the minimum-loss impedance for coax is about 77 ohms, which is why the video industry is based around 75 ohms. The impedance for maximum power handling (again, for coax) is around 30 ohms. The mean is about 50 ohms, which is why general-purpose rf plumbing is based on that value.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/13/2021 12:55, Göran Krusell wrote:
My memory tells me that the Germans in the 1930s (?) made calculations to figure out if there would be a certain characteristic impedance that would give you the lowest possible cable losses and found 60 ohm as the result. Or am I out in the blue?
Göran




Re: Type 519 -- Why 125 ohms?

Göran Krusell
 

My memory tells me that the Germans in the 1930s (?) made calculations to figure out if there would be a certain characteristic impedance that would give you the lowest possible cable losses and found 60 ohm as the result. Or am I out in the blue?
Göran


Re: Type 519 -- Why 125 ohms?

Tom Lee
 

Correction: I misread my own table. The 475's differential termination is 2x184, so 368 ohms. I'm extra curious to see where that structure's impedance falls apart now.

Thanks, Bob.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/13/2021 11:15, Tom Lee wrote:
Hi Bob,

The schematics I have for the 475 seem to show a differential termination of 184 ohms for the vertical deflection. But in any case, I don't think that it's good out to 1GHz. That said, I would be very interested in seeing the TDR results to see where the impedance starts to look screwy, if by some chance you and your colleagues happen to have taken a photo. TDR'ing CRT deflection structures is one of the many things I have on my never-to-be-completed to-do list.

Higher impedances are of course possible (by increasing the L/C ratio), but there is a complicated tradeoff among bandwidth, deflection sensitivity and physical size. Higher impedances are nice for sensitivity, but it's hard to get that in a small size without trading off bandwidth.

The following values are differential impedances for the vertical deflection lines of a few scopes:

475, 475A 184 ohms (from service manual)
7904, 7904A 385 ohms (from John Addis's article, Fast Vertical Amplifiers); the 7704 is (or should be) the same
7104 200 ohms (also from John)

-- Cheers,
Tom


Re: Type 519 -- Why 125 ohms?

Tom Lee
 

Hi Bob,

The schematics I have for the 475 seem to show a differential termination of 184 ohms for the vertical deflection. But in any case, I don't think that it's good out to 1GHz. That said, I would be very interested in seeing the TDR results to see where the impedance starts to look screwy, if by some chance you and your colleagues happen to have taken a photo. TDR'ing CRT deflection structures is one of the many things I have on my never-to-be-completed to-do list.

Higher impedances are of course possible (by increasing the L/C ratio), but there is a complicated tradeoff among bandwidth, deflection sensitivity and physical size. Higher impedances are nice for sensitivity, but it's hard to get that in a small size without trading off bandwidth.

The following values are differential impedances for the vertical deflection lines of a few scopes:

475, 475A 184 ohms (from service manual)
7904, 7904A 385 ohms (from John Addis's article, Fast Vertical Amplifiers); the 7704 is (or should be) the same
7104 200 ohms (also from John)

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/13/2021 08:51, robeughaas@gmail.com wrote:
The distributed deflection structures in CRT's used in instruments such as the 475 have impedances of over 300 ohms, as evidenced by the termination (or load) resistors in the vertical outputs. We made a measurement to confirm this using a TDR at the vintageTEK Museum.


Re: GPIB board for calibrating AM503B, or alternatives?

 

Hello Jared,

Please take Pin 4 (GND), Pin 5 (SDA) and Pin 6 (SCL) of the PCF8570.
It's easier and nothing breaks if you make a mistake.

In the meantime, I've redesigned the document. I replaced the old one.
https://groups.io/g/TekScopes/files/AM503B%20Calibration%20without%20GPIB/AM503B_AM5030%20Calibration.pdf

Best regards
Rico


Re: Looking for sensitive audio RMS meter

 

Hi Ted, thanks a lot. Great ebay find by the way. It's on its way to
me now. Thanks for sharing your experience with someone learning like
I am!

I've had a few questions, if that's ok:

1. Is it possible to measure dBV readings with this meter? I know it
doesn't have the markings for dBV, only dBm, but is it just a case of
taking the reading, adding some sort of fixed offset, and now I have
the number in dBV? I know there's a simple relationship between dBu
and dBV but I think the relationship between dBm and dBV is on a case
by case basis. I know the meter has high input impedance - so it's not
really going to load the output of the DUT like a real 600 Ohm input
meter would. But it provides a dBm "into 600 Ohm" measurement. I guess
that's just simulated?

2. The device I'd like to measure right now is the Bryston 10B. I am
not sure if they use rms noise or NRI. Thanks for teaching me about
the distinction. The specifications are here:

http://old.bryston.com/PDF/Manuals/300001[10B].pdf

go to page 4, it's in the middle. It just says "Noise: > -100 dB unweighted".

Its output impedance is 100 Ohms. I see the meter itself has 2MOhm
input impedance. Does this mean it'll be perfectly able to measure the
noise at its lowest settings? Does the measurement of RMS noise at the
lowest settings get affected by the DUT's output impedance?

I'd also like to measure the noise of DAC outputs. I think someone
mentioned that those should be measured differently, but I'm not
really sure how that is supposed to work.

I assume given its ranges, this meter can also be used to measure the
noise output of power amps (when nothing is playing through them).

3. Why the Levell specifically, and not some other device? Are there
other such good devices you would recommend?

Thanks a lot!

BTW, I compared all the meters mentioned in this thread. This is what
I came up with (see link below). Some of the numbers might be a bit
off, so double check - but it looks like the Levell is best
inexpensive meter for my use due to low self noise, good range, and
high input impedance. I'd love to hear comments.

https://imgur.com/gallery/bmdNN01

I'm also getting a 3457A (from Liam, thanks!) which will be very
useful and has a much
higher resolution - but might not always be the most practical.

On Thu, May 13, 2021 at 2:16 AM Ted Rook <rooknrol@warwick.net> wrote:

Audio Precision make some very good dedicated audio instruments which will probably serve
your purpose.

At a different and simpler level of sophistication is the Levell TM3B audio microvoltmeter,
they were made in the UK in the 1970s-90s. This is a dedicated audio microvoltmeter ideally
suited to measurement of signals and noise between about 10V rms and 10uV rms, the FSD
of the -100dB range is 15uV. Bandwidth can be set at 10k or 100k. The unit requires a 9V
battery so introduces no ground loops or noise. there is one for sale on ebay.co.uk right now,
search for Levell TM3B.

In seeking to measure in the range below -100dBu you are probably going further than you
need towards complexity and expense. It is probable that the equipment you have noticed
quoting noise performance of -110 and -120dB may be not rms noise voltage specifications
but rather a type of noise measurement used for high quality microphone preamps known as
'noise referred to input' that for a nominal 200 ohm microphone source at room temperature
has a theoretical best value of about -128dB NRI. This is calculated by measuring the gain of
the device, measuring its output noise at that gain with a 200 ohm resistor at the input
teminals, and adding the gain to the noise floor, so 60dB gain and -67dBu noise floor gives
-127dB NRI. Notice that the measurement of noise is in the range of millivolts rms, a very
different proposition to 130dBu rms noise.

It is quite likely you can find out most of what you need to know using the Levell audio
microvoltmeter.

Ted




On 12 May 2021 at 1:20, cheater cheater wrote:

Hi Liam,
thanks, I appreciate your extensive experience in this. I'm sure I'll
have a lot of questions that you'll be able to also answer along the
way. I'm setting up a mastering studio (as a hobby) and one of the
things I'd like to do is to be able to measure the noise floor of my
monitoring chain. Some elements claim to be -100 dBV noise, but I
don't necessarily trust that, so I'd like to measure that. Some other
circuits are claiming to be -120 dBV to -110 dBV self-noise. But also
for the future, I'd like to be able to measure other circuits. I'll be
replacing parts of my monitoring chain in the near future as well and
that'll require some noise measurement as well (among other things,
but low noise measurement is one of the hardest things). For the
future I'd like to be able to use the set up I learn about in this
process in designing analog audio circuits. I don't think I'll be
creating ultra low noise mic amplifiers, but I'll be creating analog
audio electronics none the less.

Thanks

On Tue, May 11, 2021 at 8:32 PM Liam Perkins <hifi@telus.net> wrote:

OK, look: what you want to do is not. easy. and short of something
modern like a Keithley nanovoltmeter there's essentially nothing off the
shelf that will get you there, ballpark but not there.

I spent 15 years measuring vacuum tube equivalent input noise and know
exactly what I'm on about. See this:

https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html

I measured 1,000s upon 1,000s of the very best of the legendary NOS
parts for people who then went on to sell them for 100s of dollars. I
provided a 13 month sliding scale warranty and during that time never
needed to replace more than a mere handful of parts because anything that
made it thru what I put parts thru was a good part.

I recommended Jim Williams work and that of Geller labs.
The Williams LT app notes you want are nos. 124 and 159 and Geller Labs you
can find on the WayBack about 2013 and the J-can article is here:

http://physicsopenlab.org/wp-content/uploads/2016/10/JCan-NV-article.pdf

Further, at the bottom of this page on my site, here:


https://www.pearl-hifi.com/06_Lit_Archive/07_Misc_Downloads/Misc_Downloads.html

see nos. 100, 103 and 105 as goldmine info on electrolytic caps and a
little known NIST paper from the days when it was NBS on a clever way to
use two-channel FFT to correlate the noise floor of the lowest noise amps
you can build down about 20dB; takes all day to run 10K averages but it
gets you there.

I spent hours on the restoration of that doc and the included refs.
That same method is well known in low noise metrology and Google on that
topic will keep you out the bar for at least the next month wading thru it
all.

Ralph Morrison is someone whose many, many works you need to know
backwards. I have about 6 of his titles in hardcopy, one of which I I
photocopied 30 years ago and had hardbound into a proper book. I also have
about 6 more in indexed PDF I'll provide free for the asking.

Although I pulled them down here:

https://b-ok.cc/

it ain't exactly legal to be puttin' them up on my site for all and sundry,
nor the highly useful works of Burkhard Vogel nor Horowitz & Hill whose
"Art of Electronics" which has been a standard for decades. The 3rd edn is
also found at Z-Lib.

Now, -what- are you trying to do, exactly; because until we know we're
all just throwing sh*t at one wall or another.

Do you need HF and if so how high, are you looking at 1/f and if so how
low, do you -really- need true rms and if so, why, because HP's earlier
400-series rms-reading, average-responding AC voltmeters will get you
within about a dB if you're measuring noise.

The 400GL and the 400F provide FSDs of -80dB, I have two of each and
plans to swap out the input JFETS in the 'Fs for modern much quieter parts
from Linear Integrated Systems.

Put Matt's +60db LN gain block in front of one of those and you are
home and dry.

Liam

On Tue, May 11, 2021 at 9:44 AM cheater cheater <cheater00social@gmail.com>
wrote:

On Tue, May 11, 2021 at 3:07 PM Matt <mhofmann@sbcglobal.net> wrote:

I have used an HP 3400A to measure the noise in circuits for several
applications since the 1970s, both for business and pleasure. I found it
useful for determining the equivalent input noise for various microphone
preamps that I had built. Typically I used a low noise solid-state preamp
on the front end of the HP 3400 with a low-pass filter on the input of the
3400A to reduce the bandwidth to the audible range. With this arrangement
I could get 60 dB of gain on the preamp, and I could measure the equivalent
input noise of the microphone preamp I was testing. I could get quite a
bit of sensitivity with this arrangement. I would set the HP 3400A to 1
mVrms and add another 60 dB of gain with the low noise preamp, resulting in
1 uVrms full-scale sensitivity on the meter.

It seems like this is the kind of scenario I should be looking at.
What LNA were you using?

Liam mentioned the J-Can and he had parts for it available. I think
this should be the way to go.

Is it possible to modify the HP 3400A to have a dBV scale?

Thanks.

I used this arrangement for solid-state microphone preamps that I was
designing and building as well as a tube based microphone preamp that later
on I built for my boss.
I have also used an FFT based spectrum analyzer program on an old laptop
PC that was useful in identifying the noise floor of these preamps.
I bought the HP 3400A on eBay a number of years ago for about $50 (I
could have been a bit more).

Matt




















Re: SA 492P with probe P6201

J Mcvein
 

Set the blue box for AC coupling, no DC offset. ext term., you should be set. -J-

-----Original Message-----
From: "Attilio" <a.alovisetti@alice.it>
Sent: Thursday, May 13, 2021 10:14am
To: TekScopes@groups.io
Subject: [TekScopes] SA 492P with probe P6201



Hi all, I have repaired my SA 492P and am using it with the TR503 (re-converted from TR502, modification made for use with the 7L13 on mainframe 7613), I saw that on the back of the 492P there is a LEMO connector for power an active probe.
I have an active P6201 probe, can I use it connected to the 492P? I should use a DC blocker between the probe output and the RF input of the 492P, but is this enough not to damage the 1st Mixer of the 492P? What setting should I use on the probe?
If you have any advice on using the P6201 probe that would be great.

Thanks for your attention.

-- Cheers
Attilio


Re: Type 519 -- Why 125 ohms?

 

The distributed deflection structures in CRT's used in instruments such as the 475 have impedances of over 300 ohms, as evidenced by the termination (or load) resistors in the vertical outputs. We made a measurement to confirm this using a TDR at the vintageTEK Museum.

--
Bob Haas


Strange TD in 067-0587-01

Albert Otten
 

I try to resurrect a calibration fixture 067-0587-01. Some parts have been removed in the passed, along with a TD CR280 which I removed myself but kept apart all the time. Now I reinserted that TD but is refused to switch. With my 576 I discovered that the polarity of this TD was opposite to what I expected for a DO-17. With a magnifier glass I saw that the arrow indeed pointed towards the isolated lead instead of the mass lead. I have never seen this before. The TD in my other calibration fixture has the "normal" arrow direction.
Further the marking is 152-199 without any doubt, while the 152-0199-00 is listed as a rectifier diode.
The manual mentions 152-0177-00.
Is the other arrow direction indeed unusual?

Albert


Re: GPIB board for calibrating AM503B, or alternatives?

Jared Cabot
 

Looks good so far!

So far I got the firmware updated on my Bus Pirate, and found the SCL and SDA pins on the 87C528 Philips chip in one of my AM503B modules (Pins 7 and 8 respectively).
I'll have to hook it all up next and see if I can poke the bear.


Re: 7934 troubleshooting

Karin Johnson
 

First off, an immense thank you to all of the encouragement. I'll get to all of the questions soon. Stay tuned.
On the troubleshooting front, I think I may have found what is causing the inverter to not start. It has to do with the "Start" circuit related to the programmable unijunction transisistor and VR38. I have another 7934 power supply to use as a test bench, so I can compare voltages and waveforms with this other unit. It seems that the unijunction transistor never fires because the voltage across VR38 never reaches 33 volts. I've checked all of the semiconductors on the inverter board. The testing was with a basic ohm meter and was done "in circuit". I've allowed for sneak paths and all the semis
seem OK. It is a bit difficult to in circuit test the unijunction, as one path is through VR38 in the forward direction. Also getting the inverter board out of the power supply is tedious, as it is intimately connected to the heat sink. I've ordered parts and am going to write a Spice simulation of this circuit, as well as take some photos of the waveforms and do more detailed recording of voltages from the somewhat working other unit.
I thought this missive might be of interest. Dave Peterson I will get back to you. I've been down that road before and have some suggestions.

Regards,
Karin


SA 492P with probe P6201

Attilio
 

Hi all, I have repaired my SA 492P and am using it with the TR503 (re-converted from TR502, modification made for use with the 7L13 on mainframe 7613), I saw that on the back of the 492P there is a LEMO connector for power an active probe.
I have an active P6201 probe, can I use it connected to the 492P? I should use a DC blocker between the probe output and the RF input of the 492P, but is this enough not to damage the 1st Mixer of the 492P? What setting should I use on the probe?
If you have any advice on using the P6201 probe that would be great.

Thanks for your attention.

-- Cheers
Attilio


Re: Tek 576 CT CRT replacement with an LCD or LED or VGA adaptor ?

garp66
 

I see that Ed has some pertinent information about doing this for the 576:

in message: 01/08/20 #162991
https://groups.io/g/TekScopes/message/162991?p=,,,20,0,0,0::Created,,576+LCD+VGA,20,2,0,69490299

Does anyone have any further technical details ?

thank you,


Tek 576 CT CRT replacement with an LCD or LED or VGA adaptor ?

garp66
 

Could the Tek 576 CT CRT be replaced with an LCD or LED display module, Or a VGA adaptor ?

-- What are the signal details(amplitude, frequency) going to the 576 CRT that could be picked off for such a conversion ?

-- Presumably a small conversion module would have to be built, interfacing the old 576 signals to a standard VGA LCD module.
How difficult could that be ?

-- Could an Epiphan video converter module(various versions),
using one of their "obscure video modes" be used ( perhaps with a small conversion PCB) to do this ?

rik


Re: Recapping Tektronix 2465

 

On Wed, May 12, 2021 at 05:27 PM, iv3ddm wrote:


I found that the old capacitors removed have a capacity equal to or greater
than the imprinted value, while the new ones on average almost always have a
capacity lower than the rated value
Yes, that's a fairly common representation.
Electrolytics are generally specified as +/- 20% capacitance.
To save costs, manufacturers will cheat slightly on the low side - it's a fact of life.

THEREFORE, feel free to select capacitors of slightly higher capacitance, in order to meet the original bare number value.
Furthermore, if you understand the circuit, feel free again to double or triple the original capacitance value, for increased performance and reliability.
This is especially applicable in SMPS applications.

Remember, it's all a matter of cost - saving $0.11 (total per PSU) on low-spec units multiplied by 1 million PSU's manufactured, is a lot of money saved.
But it's also a lot of environmental waste, when stuff gets trashed before its time.
And somebody (our grandchildren) is going to have to pay for the environmental clean-up.

When I overhaul TV PCB's, I have a standard procedure to at least double the capacitance values in certain parts of the circuit.
Especially at the high frequencies in these PCB's, ripple current capabilities become paramount, and these caps will run cooler and last longer than the original specc'd units..
My incremental cost increase for using higher spec caps is less than a couple of $, which is absolutely insignificant when related to the total repair cost, so why be stingy and skimp?

Film capacitors are generally reliable (except for these paper RIFA's and others), and will show similar ESR readings, irrespective of age.

Of course, YMMV.


Re: 7934 troubleshooting

Dave Peterson
 

Karin,

I'll be very interested to learn what you find. I currently have a 7934 power supply set aside from my bench as I await a proper curve tracer. I cycled many times through the troubleshooting guide in the service manual (online - what a pain), and still don't quite know what's wrong.

What was interesting was that removing Q54 from the A14A1 Control Rectifier Board recovered all the LV test points. The 108V is over voltage though, and continuously climbs. The PS makes a nasty buzzing sound. I only tested it in short bursts. I think the issue is in either the Over Voltage Stop circuit and/or the inverter Q34 and Q40 themselves.

I have all the suggested transistors dismounted from the PS. That's part of the troubleshooting procedure in the SM. I've tested them with a little breadboarded curve tracer and they look quite flat. But my breadboard curve tracer is very limited. Traces 2N3904's just fine. But I suspect it doesn't have the oompf to drive these power transistors. So I'm working on getting my hands on a proper curve tracer. Fingers crossed. I will or I won't by this time tomorrow. The SM troubleshooting seems to suggest it's the inverter that's the problem. But it seems the only test methodology is to remove and test the components individually. Not very enlightening.

Still on the switched power supply learning curve.

WRT to the devices that have this power supply setup: I also have a 7854 on hand for the time being. I'd take it's PS out and compare signals, but I don't want to break it! But the point is: it's obvious that they both have the same power supply. There are minor difference I can find when I look them up in their respective service manuals. But these two scopes do seem to have the same unit. And it is a self contained box that slides out the back of the scope. It is possible to disconnect the line cable from the switch by unplugging it and undoing some ground screws. At least in the scope I have at hand. I find it a pretty nice design, construction wise.

I'm curious to find out what the common failure modes of this PS are. Might help to figure out what's going on with this one.

Dave

On Wednesday, May 12, 2021, 03:31:56 PM PDT, Dave Daniel <kc0wjn@gmail.com> wrote:

The 7934s are the fastest (500 MHz) of the Tektronix 7xxx storage ‘scopes and they are not common. The more common 7834s have a 400 MHz bandwidth.

I don’t know if 7934s are more or less difficult to repair compared to other 7xxx ‘scopes. I would guess that having the storage feature makes repairs a little more complicated than, say, a 7904A, but I don’t know for sure.

DaveD

On May 12, 2021, at 17:59, David Slipper <softfoot@hotmail.com> wrote:

As per the subject the 7934 ...

On 12/05/2021 22:23, Dave Daniel wrote:
To what devices do you refer in your post?

On May 12, 2021, at 17:09, David Slipper <softfoot@hotmail.com> wrote:
Is this series of devices particularly hard to access or not well documented or very complex ??

I've been tempted to get one but if they are that difficult I may have to think again.

Regards,
Dave



On 12/05/2021 22:00, Jeff Dutky wrote:
Karin,

I have a 7623A half open on the bench that I am having to pretend not to notice until I have calmed down enough to do a proper diagnosis of its power supply. I've been "calming down" for a few weeks. This is why it's good to have other projects to work on: it gives you time to clear your head.

-- Jeff Dutky









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