Author Topic: Test Equipment Anonymous (TEA) group therapy thread  (Read 1710564 times)

Cubdriver, Carl_Smith, ArthurDent, bitseeker, mnementh, med6753, xrunner, Brumby, jjoonathan, wch, dcbrown73 (+ 1 Hidden) and 18 Guests are viewing this topic.

Offline zucca

  • Supporter
  • ****
  • Posts: 1939
  • Country: it
  • Country: it
  • EE meid in Itali
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37300 on: August 23, 2019, 08:04:51 am »
For European TEA, if you need a cheap (<400€) 66309D please join me here
Can't know what you don't love. St. Augustine
Can't love what you don't know. Zucca
 

Offline BU508A

  • Frequent Contributor
  • **
  • Posts: 768
  • Country: de
  • Country: de
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37301 on: August 23, 2019, 08:40:57 am »
The test gear drought has ended. Just bought another scope  :-DD

So the HP collection grows. I own an HP 1740A. Powers up untested. No trace. All knobs intact. Looks like it might just be rammed in XY mode. Fingers crossed  :scared:

Congrats!

Quote
Edit: just realised I'm turning into HP fanboy. That's err 3x power supplies, 1x function generator, 1x scope, 1x meter, 1x calculator now  :-DD (I won't mention the printer or the shonky Elitebook though).

Welcome to the club. There are worse things you could turn into. ;D


Yes. For example, one could turn into a R&S fanboy ...  :scared:    :palm:
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 

Offline BU508A

  • Frequent Contributor
  • **
  • Posts: 768
  • Country: de
  • Country: de
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37302 on: August 23, 2019, 08:43:38 am »
I just pulled together my Taxes for last year. I spent almost $200 just on probes/test leads and stuff to make test leads/patch cables. Another $300 on meters. And $900 on wrenches and power tools.
mnem

I would say, your profile fits perfectly into TEA.
Go ahead.

 :-DD
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 
The following users thanked this post: mnementh

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15674
  • Country: nz
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37303 on: August 23, 2019, 08:49:45 am »
I just pulled together my Taxes for last year. I spent almost $200 just on probes/test leads and stuff to make test leads/patch cables. Another $300 on meters. And $900 on wrenches and power tools. 
mnem
Amatuer !
I spent much more on just one scope !  :P
Avid Rabid Hobbyist
 
The following users thanked this post: mnementh

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37304 on: August 23, 2019, 09:29:26 am »
Started looking at U740 and I think I found some issue. This is pulse at TP5 as well as at CR751. 5MV/2ms and 5MV/1ms. That doesn't look right at all. Mostly ripple noise. Quick check of other pins of both U740 and U738 are showing same crap. I'm going to pick up in this area in the AM. It definitely looks fubar. Do you agree?  :-//

All stuff around that area, i.e. before c761/r761 does not depend on whether or not it is triggered; u780 is irrelevant.

u740 etc are classic long-tail pair differential amplifiers. The inputs are differential voltage inputs, the outputs are differential current outputs. If the input voltages are equal, the output currents should be equal. The output currents are converted into input voltages for the next IC by resistors, i.e. r731, r736, then r745, r746, r749 , then r751, r752 plus others around cr751. Using a single-ended scope probe can only measure the differential output current indirectly! The differential input voltage should be <100mV for linear operation; if it is more than 200mV the outputs will be fully saturated/off.

A good way to test that is to use the 1kHz cal out driving the external trig input (as per fig 6 top left). You should see a square wave on u740.5 and u740.9.  At those two points I see unequal 200mV-800mV square waves, and the relative amplitude depends on the position of the trigger level control.

If you don't see those square waves, then start at u730.14, u730.16 (inputs) then u730.5, u730.9 (outputs), then u738, then u740.

I just scoped U740.5 and 9 with set to ext trig and the cal input and I see a square wave on each output. So that is working. However, varying the level control has no effect. You stated that it should change with the level control so should I go after that?
An old gray beard with an attitude.
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37305 on: August 23, 2019, 09:45:00 am »
More info: U730.9 the amplitude changes somewhat with the level control. U730.5 does not change. U730.14 which is the input from the trig level control does change quite a bit.
An old gray beard with an attitude.
 

Offline bd139

  • Super Contributor
  • ***
  • Posts: 11123
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37306 on: August 23, 2019, 09:59:33 am »
Just got the 1740A. Appears to have some problems with it. Comes up but not HT. Debug time!  :-+
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37307 on: August 23, 2019, 10:22:19 am »
This 485 Trigger problem is finally starting to make sense. I think with tggzzz's help the problem has at least been isolated. It looks like U730 might be bad. It's output is not changing, especially on pin 5, in response to a change in the trigger level control input on pin 14. This apparently is causing the trigger level to be fixed which just so happens to be at a "triggered" point which in turn is jamming up the entire trigger circuit to think it's "triggered" which is why the trigger light is always on. That's at least how I interpret it but I am just a simple technician.  :-DD

I didn't sleep well last night so I'm going to go lay down for a while and come back to this. I'll let you learned guys review my findings and either agree or suggest something else. If we are in agreement that U730 doesn't look good before condemning it I'll check all the supporting components around it. But I think I FINALLY have this bastard nailed down.  :phew:

Edit...partial schematic attached. Pin 14 of U730 varies with the level control. Pin 5 is fixed. Pin 9 varies a little.
« Last Edit: August 23, 2019, 10:28:41 am by med6753 »
An old gray beard with an attitude.
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37308 on: August 23, 2019, 10:46:18 am »
Just got the 1740A. Appears to have some problems with it. Comes up but not HT. Debug time!  :-+

Hopefully it won't be a circle jerk like my 485 issue has been.  :scared:
An old gray beard with an attitude.
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9648
  • Country: gb
  • Country: gb
    • Having fun doing more, with less
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37309 on: August 23, 2019, 10:57:11 am »
Started looking at U740 and I think I found some issue. This is pulse at TP5 as well as at CR751. 5MV/2ms and 5MV/1ms. That doesn't look right at all. Mostly ripple noise. Quick check of other pins of both U740 and U738 are showing same crap. I'm going to pick up in this area in the AM. It definitely looks fubar. Do you agree?  :-//

All stuff around that area, i.e. before c761/r761 does not depend on whether or not it is triggered; u780 is irrelevant.

u740 etc are classic long-tail pair differential amplifiers. The inputs are differential voltage inputs, the outputs are differential current outputs. If the input voltages are equal, the output currents should be equal. The output currents are converted into input voltages for the next IC by resistors, i.e. r731, r736, then r745, r746, r749 , then r751, r752 plus others around cr751. Using a single-ended scope probe can only measure the differential output current indirectly! The differential input voltage should be <100mV for linear operation; if it is more than 200mV the outputs will be fully saturated/off.

A good way to test that is to use the 1kHz cal out driving the external trig input (as per fig 6 top left). You should see a square wave on u740.5 and u740.9.  At those two points I see unequal 200mV-800mV square waves, and the relative amplitude depends on the position of the trigger level control.

If you don't see those square waves, then start at u730.14, u730.16 (inputs) then u730.5, u730.9 (outputs), then u738, then u740.

I just scoped U740.5 and 9 with set to ext trig and the cal input and I see a square wave on each output. So that is working. However, varying the level control has no effect. You stated that it should change with the level control so should I go after that?

More info: U730.9 the amplitude changes somewhat with the level control. U730.5 does not change. U730.14 which is the input from the trig level control does change quite a bit.

If you have a square wave of sufficient amplitude at u740 outputs, that is sufficient to kick off the triggering. Any other effects would be second-order, and might be worth looking at when triggering is functional.

The next stage in this chain, before you get to u780, would be to look around the tunnel diodes.

Have you gone through the procedures to set the "a trig sens" "a arming" and "a output" trimpots?

Put a 10kHz sinewave into ch1 and adjust the vertical to have the trace around ~2.5 divisions peak-peak, trig from ch1. U738.5 should show a ~1Vp-p sinewave. If it is distorted by clipping then adjusting the level control should allow you to "recentre" it and let it be more or less symmetrical. Don't get too hung up about those levels; fiddle until it looks right, ideally when triggering is working correctly :)

Looking at the output of u740.5 will show a grossly distorted sine wave with significant clipping and worse. The key feature to look for is a sharp transition somewhere, which is the tunnel diode being non-linear. That's even more apparent on the other side of r752, where cr751 should be causing there to be a vertical gap in the waveform.

Skipping ahead, look at the junction of r762 r760. It should be a 300mVpp "square" waveform with sharp transitions, period related to the sweep duration. There should be four separate levels, three similar related to arming all the tunnel diodes, and one significantly different. The relative durations of those "phases" depends on the input frequency and the sweep duration. Personally I'd be pleasantly surprised if you saw that waveform, since it indicates everything is working!
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9648
  • Country: gb
  • Country: gb
    • Having fun doing more, with less
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37310 on: August 23, 2019, 11:15:23 am »
This 485 Trigger problem is finally starting to make sense. I think with tggzzz's help the problem has at least been isolated. It looks like U730 might be bad. It's output is not changing, especially on pin 5, in response to a change in the trigger level control input on pin 14. This apparently is causing the trigger level to be fixed which just so happens to be at a "triggered" point which in turn is jamming up the entire trigger circuit to think it's "triggered" which is why the trigger light is always on. That's at least how I interpret it but I am just a simple technician.  :-DD

Put a 2.5 division sinewave into channel 1 and use trig = ch1; that will be easier to diagnose than a squarewave. You should be able to adjust the controls so the outputs of u730 and u738 show a sinewave. After u740 all hell breaks loose :)

ISTR having a "horizontal degeneration" resistor go awol, r729/732/733/744, or something in that area. Before condemning u730 check all resistors near the inputs and outputs. Best way to localise that is to start at the bottom, move upwards, and find where the waveforms are no longer a sinewave. Don't forget to adjust the trig level so that for each stage the two base voltages are similar. (i.e. ~0V differential voltage), ditto two collector voltages, ditto to emitter voltages. If you can't make them equal, that's related to a problem in the IC or resistors somewhere nearby.

If you are unfamiliar with long-tail pairs, then speed read 12.2 and 12.3 in https://wiki.analog.com/university/courses/electronics/text/chapter-12 but don't get hung up on all the extra components in the scope; they are just there to tweak performance
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37311 on: August 23, 2019, 12:09:44 pm »
Sorry, but you are confusing me. As currently set up U730 has somewhat unequal outputs on pins 5 and 9 and the level control has no real affect. U738 has EQUAL levels on both pins 5 and 9. Again, level control has no effect. U740 has grossly UNEQUAL levels. Pin 9 much less than pin 5. Level control has no effect. What should I go after? The fact that the level control has little or no effect or the unequal output of U740?  :-// 
An old gray beard with an attitude.
 

Offline bd139

  • Super Contributor
  • ***
  • Posts: 11123
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37312 on: August 23, 2019, 12:14:38 pm »
Just got the 1740A. Appears to have some problems with it. Comes up but not HT. Debug time!  :-+

Hopefully it won't be a circle jerk like my 485 issue has been.  :scared:

Nope was easy-ish.

Bar the hour I just spent on the blower to a provider on a finger pointing misssion (work), we have a victory at least.

Power supply shot. Took the thing to bits (I bloody love 1740A construction) and yanked off the interface board thus disconnecting both vertical and horizontal boards. Discovered 5V was at 8V (fuck!) and -15V was at 1.02V (double fuck). Powered it down. Reading the service manual it looks like the two supplies are related so I had a feel around. Checked pass transistors. Both fine. Checked ESR on all the power supply caps. All good. Checked the LM723 on the -15V rail. Burning hot! Pulled the pass transistor off and jumped the -15V rail with a power supply and bingo it came up and everything works apart from the flood gun illumination (should be easy to debug). Looks like the high 5V rail has done no damage fortunately  :phew:

Patient on the bench (need bigger bench!):



Bingo:



Now to work out what is dead. Hopefully not the LM723 as they are TO-100 canned ones and are a good tenner a go  :--
 

Offline Specmaster

  • Super Contributor
  • ***
  • Posts: 7335
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37313 on: August 23, 2019, 12:18:03 pm »
The test gear drought has ended. Just bought another scope  :-DD

So the HP collection grows. I own an HP 1740A. Powers up untested. No trace. All knobs intact. Looks like it might just be rammed in XY mode. Fingers crossed  :scared:

Needs new feet and worst case it's strip and sell parts off.

Edit: just realised I'm turning into HP fanboy. That's err 3x power supplies, 1x function generator, 1x scope, 1x meter, 1x calculator now  :-DD (I won't mention the printer or the shonky Elitebook though).

Edit 2: had one of these before for ref. Picture of the last one I restored:


Well done, they are great scopes, I still have the spare boards from my donor scope if needed, not 100% sure if they all work OK or not as donor was in a really filthy state so I gutted it and dumped the carcass

Sent from my POT-LX1 using Tapatalk

Who let Murphy in?
 

Offline Specmaster

  • Super Contributor
  • ***
  • Posts: 7335
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37314 on: August 23, 2019, 12:37:11 pm »
Just got the 1740A. Appears to have some problems with it. Comes up but not HT. Debug time!  :-+

Hopefully it won't be a circle jerk like my 485 issue has been.  :scared:

Nope was easy-ish.

Bar the hour I just spent on the blower to a provider on a finger pointing misssion (work), we have a victory at least.

Power supply shot. Took the thing to bits (I bloody love 1740A construction) and yanked off the interface board thus disconnecting both vertical and horizontal boards. Discovered 5V was at 8V (fuck!) and -15V was at 1.02V (double fuck). Powered it down. Reading the service manual it looks like the two supplies are related so I had a feel around. Checked pass transistors. Both fine. Checked ESR on all the power supply caps. All good. Checked the LM723 on the -15V rail. Burning hot! Pulled the pass transistor off and jumped the -15V rail with a power supply and bingo it came up and everything works apart from the flood gun illumination (should be easy to debug). Looks like the high 5V rail has done no damage fortunately  :phew:

Patient on the bench (need bigger bench!):



Bingo:



Now to work out what is dead. Hopefully not the LM723 as they are TO-100 canned ones and are a good tenner a go  :--
Check the connections to the rectifiers, although they may look OK, it's a known problem that the TH connections can suffer. Also I think the the 5v line is referenced to one of the higher rails, RTM for more info. Another possible source are the interconnections and bridge pieces, it is possible to 1 be pin off in some cases.

Sent from my POT-LX1 using Tapatalk
Who let Murphy in?
 

Offline bd139

  • Super Contributor
  • ***
  • Posts: 11123
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37315 on: August 23, 2019, 12:54:31 pm »
Check the connections to the rectifiers, although they may look OK, it's a known problem that the TH connections can suffer. Also I think the the 5v line is referenced to one of the higher rails, RTM for more info. Another possible source are the interconnections and bridge pieces, it is possible to 1 be pin off in some cases.

Sent from my POT-LX1 using Tapatalk

Plan - will check  :-+
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37316 on: August 23, 2019, 12:57:30 pm »
Sorry, but you are confusing me. As currently set up U730 has somewhat unequal outputs on pins 5 and 9 and the level control has no real affect. U738 has EQUAL levels on both pins 5 and 9. Again, level control has no effect. U740 has grossly UNEQUAL levels. Pin 9 much less than pin 5. Level control has no effect. What should I go after? The fact that the level control has little or no effect or the unequal output of U740?  :-//

With the same conditions as above here is what tunnel diode CR751 is doing....

Cathode side   .2V  .5ms/div



Anode side   10mv  .5ms/div



Both CR762 and 772 look same as I posted yesterday.
An old gray beard with an attitude.
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37317 on: August 23, 2019, 01:01:43 pm »
Do you know how close I am to tossing this 485 out a 2nd story window?  :o :-DD

That close...... |O
An old gray beard with an attitude.
 

Offline bd139

  • Super Contributor
  • ***
  • Posts: 11123
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37318 on: August 23, 2019, 01:03:57 pm »
Well fuck  :--

A+ to Specmaster. Straight to the problem. Bridge is dead short. Fortunately (I think) the transformer secondary is still good as it smoked the connector instead of the winding  :-DD

I'm not sure what to do exactly here yet. I suspect a replacement connector may be the correct solution. And probably capacitor!

« Last Edit: August 23, 2019, 01:10:26 pm by bd139 »
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9648
  • Country: gb
  • Country: gb
    • Having fun doing more, with less
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37319 on: August 23, 2019, 01:37:17 pm »
Sorry, but you are confusing me. As currently set up U730 has somewhat unequal outputs on pins 5 and 9 and the level control has no real affect. U738 has EQUAL levels on both pins 5 and 9. Again, level control has no effect. U740 has grossly UNEQUAL levels. Pin 9 much less than pin 5. Level control has no effect. What should I go after? The fact that the level control has little or no effect or the unequal output of U740?  :-//

Measure, in this order...

With no input, on my 485 the inputs to u730.16 is about 0.7V (schematic says 0.77V), and u730.14 varies between 0.2V and 1.5V depending on the trig level control.

The u730 outputs u730.5 and .9 go from ~3.3V to ~4.8V in antiphase (schematic states 4.12V), depending on the trigger level pot. When the trigger level pot is in the middle, the voltages are equal. The u738 equivalents are 6.2V and 7.8V. The u740 equivalents are ~10.4 and ~11.4V, but I suspect there are some non-linearities due to the tunnel diode loading them.

If u730 inputs are roughly that and the outputs aren't, then check the u730.12, which should be 5*560/(560+430). U730.2 and u730.3 should both be -0.02V according to the schematic.

But apply a 2.5 vertical division sinewave with trigger AC coupling. You should see a sinewave as you go up the 730/738/740 stack. It is easier to see linear operation or clipping etc with a sinewave (or triangle wave or ramp) than with a square wave.
« Last Edit: August 23, 2019, 02:08:11 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Online med6753

  • Super Contributor
  • ***
  • Posts: 3714
  • Country: us
  • Country: us
  • Tek nut
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37320 on: August 23, 2019, 02:05:20 pm »
Sorry, but you are confusing me. As currently set up U730 has somewhat unequal outputs on pins 5 and 9 and the level control has no real affect. U738 has EQUAL levels on both pins 5 and 9. Again, level control has no effect. U740 has grossly UNEQUAL levels. Pin 9 much less than pin 5. Level control has no effect. What should I go after? The fact that the level control has little or no effect or the unequal output of U740?  :-//

Measure, in this order...

With no input, on my 485 the inputs to u730.16 is about 0.7V (schematic says 0.77V), and u730.14 varies between 0.2V and 1.5V depending on the trig level control.

The u730 outputs u730.5 and .9 go from ~3.3V to ~4.8V in antiphase (schematic states 4.12V), depending on the trigger level pot. When the trigger level pot is in the middle, the voltages are equal. The u738 equivalents are 6.2V and 7.8V. The u740 equivalents are ~10.4 and ~11.4V, but I suspect there are some non-linearities due to the tunnel diode loading them.

If u730 inputs are roughly that and the outputs aren't, then check the u730.12, which should be 5*560/(560+430). U730.2 and u730.3 should both be -0.02V according to the schematic.

But apply a 2.5 vertical division sinewave with trigger AC coupling. You should see a sinewave as you go up the 730/738/740 stack. It is easier to see clipping etc with a sinewave (or triangle wave or ramp) than a square wave.

Done. Everything agrees with your readings including the distorted sine wave at the output of U740. On to that tunnel diode.
An old gray beard with an attitude.
 

Offline bd139

  • Super Contributor
  • ***
  • Posts: 11123
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37321 on: August 23, 2019, 02:12:33 pm »
Taking the HP 1740A off to its own thread here: https://www.eevblog.com/forum/testgear/hp-1740a-power-supply-burn-up/
 
The following users thanked this post: bitseeker

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9648
  • Country: gb
  • Country: gb
    • Having fun doing more, with less
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37322 on: August 23, 2019, 02:20:05 pm »
Done. Everything agrees with your readings including the distorted sine wave at the output of U740. On to that tunnel diode.

Good.

With the 2.5 division 1kHz sinewave and trigger level roughly centered, u740.9 looks like this... Ignore the intensity variation, but note the 1 division gaps in the vertical dimension; they are due to the tunnel diode nonlinearity. If you don't see those, then the triggering won't be working correctly - could be the TD biassing (follow the manual procedure) or u780 outputs or another fault in that region.

BTW, if you do chuck it out the window please make sure it is in a box with my name on it, and there's a waiting UPS van :)
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9648
  • Country: gb
  • Country: gb
    • Having fun doing more, with less
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37323 on: August 23, 2019, 02:21:09 pm »
Taking the HP 1740A off to its own thread here: https://www.eevblog.com/forum/testgear/hp-1740a-power-supply-burn-up/

A certain D. Jones did a video about a 1740 where the rectifier was faulty.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline bd139

  • Super Contributor
  • ***
  • Posts: 11123
  • Country: gb
  • Country: gb
Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #37324 on: August 23, 2019, 02:31:59 pm »
Wasn't rectifier. They all just tested good. Also it powers up through them fine. I've desoldered them for rework but this appears to have burned up due to a bad solder joint or connector pin or two. Looking at replacement Molex KK 394 headers now and some horrid looking rework
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf