Test Equipment Anonymous (TEA) group therapy thread

[W6EL]

<SNIP>

Calibration is next. I am working my way through this LM299 board from China. So far it seems like this board needs a *long* warmup period before it's stable. Like, an hour or so. I sent the seller an email, I want to make sure I'm using the jumpers correctly and all that. I plan to surround it with ESD-safe black foam and place it inside a metal oatmeal can. 15V regulator on top. Then I can bring it around to calibrated meters and hopefully use that calibration at home. We will see. It will need to demonstrate that it comes up the same way every day first.

Don't use the black conductive foam for thermal (or other) insulation. It will cause leakage. ESD should not be too muh of an issue for fixed insulation on an installed device. Use standard non-conductive foam for insulation.

Robert.

Robert, you seriously saved my ass just now.

I was wondering why it was bopping all over the place and not really settling down. I took it out of the foam (I just had a piece under it and over it on the bench) and it got a lot quieter. I stuck some DMM probes in the foam and I read about 2.5k. So yeah, this was an awful idea! Now I've got standoffs on it and it's sitting between the foam (but not touching it, except for the four standoffs which are connected to circuit ground) with the entire thing in a pink bag, and we're already in the 10uV range of stability. I'll give it a few minutes and I bet we get even lower.

Dang. Good intuition there. I'll send photos later.

[factory]

For the last few weeks I have been working on making a clone of the HP 03400-66512 Rev D (A6) board, for the 3400A RMS voltmeter, I had a Rev C board which helped greatly with the layout and error checking, Hal on the HP groups.io helped with pictures of the Rev D board too.

Most of the parts should be easily available for this version, the ICs are a 7650 chopper amp & LT1012 or equivalent(s). The 2N4384 transistors are obsolete, but I have some BCY59X in my spares collection that should do, the Schottky diode is some wired HP part number of 1901-0518 (5082-5509), no data is available so I don't know what is special about this part, of course Broadcom EOL'd the HP parts, I'm hoping a BAT41 or 1N5711 will do for this.

Will be ordering these with the fools gold (ENIG) option, as solder finish & gold edge connectors are not a good idea, apparently they get stuck together, original HP boards were either nickel or hard gold plated for the edge connectors.

P.S. The recent CuriousMarc video on the HP 410C was very interesting, good to see a neon optical chopper assembly being repaired for a change.   

David

[W6EL]

For the last few weeks I have been working on making a clone of the HP 03400-66512 Rev D (A6) board, for the 3400A RMS voltmeter, I had a Rev C board which helped greatly with the layout and error checking, Hal on the HP groups.io helped with pictures of the Rev D board too.

Most of the parts should be easily available for this version, the ICs are a 7650 chopper amp & LT1012 or equivalent(s). The 2N4384 transistors are obsolete, but I have some BCY59X in my spares collection that should do, the Schottky diode is some wired HP part number of 1901-0518 (5082-5509), no data is available so I don't know what is special about this part, of course Broadcom EOL'd the HP parts, I'm hoping a BAT41 or 1N5711 will do for this.

Will be ordering these with the fools gold (ENIG) option, as solder finish & gold edge connectors are not a good idea, apparently they get stuck together, original HP boards were either nickel or hard gold plated for the edge connectors.

P.S. The recent CuriousMarc video on the HP 410C was very interesting, good to see a neon optical chopper assembly being repaired for a change.   

David

Looks beautiful. If you have success with it, sell a kit! I bet those transistors are not needing to be too specific.

I watched that CuriousMarc video just last night and thought "he really needs a 3400A" where he could appreciate the chopper and the calorimeter-style RMS sensor. 

[factory]

Yes he needs a 3400A, preferably an early one to go with all the 1960s HP TE he's restored recently, I suspect the HP microfiche he has access to will reveal the info on the neons used.

I've still got to put together a Mouser list for the 03400-66512 board, the ground stand-off I'll have to make, couldn't see an off the shelf version long enough. The Molex test pins, I've salvaged some originals from the 180 series SA junk I bought from PP auctions (pile of units that had been used as spares by the last owner).
I've not ordered the boards yet, will probably get 5 or 10 made depending on price from JLC, is it worth going with the 2U ENIG?

David

[W6EL]

Yes he needs a 3400A, preferably an early one to go with all the 1960s HP TE he's restored recently, I suspect the HP microfiche he has access to will reveal the info on the neons used.

I've still got to put together a Mouser list for the 03400-66512 board, the ground stand-off I'll have to make, couldn't see an off the shelf version long enough. The Molex test pins, I've salvaged some originals from the 180 series SA junk I bought from PP auctions (pile of units that had been used as spares by the last owner).
I've not ordered the boards yet, will probably get 5 or 10 made depending on price from JLC, is it worth going with the 2U ENIG?

David

At work there are always concerns with potential incompatibility with solder, HASL is recommended for high-rel. But I suspect it is fine of course.

Question, why are the traces seemingly constrained to right-angles? Is this to replicate the original artwork? Did you consider any upgrades as you went along?

[TERRA Operative]

Ooh, I'll check that! Thanks for the heads up!

I've already replaced the cap (and the other Rifa cap on the mains input) with an equivalent modern part, I wonder if there are schematics for this PSU module around somewhere?

The power supply is based on the Computer Products / Artesyn NFS series. Circuit diagrams are hard to find. One unusual feature is the feedback loop and isolation. It is based on a small toroidial transformer with a iron dust or ferrite core. The core forms part of the drive circuit osciator and the feedback. It appears to use saturation of the core caused by current in the low voltage side winding to control the pulse width. Very clever design but  right PITA to troubleshoot I've had a couple, from HP8920A/B radio test sets with blown snubber RIFAs. This results in the MOSFET going short to the gate. That then literally blows up two or three resistors, a oscillator transistor and one of the windings of the feedback transformer. Re-winding the little transformer is possible but a bit of a pain.

Robert.

Good info!

My PSU seems to be working fine so far, I guess the dying Rifa luckily passed without causing any collateral damage.

[electronomicon]

I received the GPIB module for my 54622D today, together with the original micro grabbers for the data cable that had previously been missing.
Also got myself a usb floppy drive and a cheap floppy to update the firmware. Worked out fine, even though I have to say the self-extracting *.exe files for the firmware and quick help (from Keysight’s website) seem quite sketchy from today’s stand point .

The scope is btw. also in an awesome state. Didn’t actually seem that great from the seller’s photos, but after a thorough cleaning it looks superb .

Edit: The only thing I’m now still waiting for is a quieter fan .

[Black Phoenix]

Ooh, I'll check that! Thanks for the heads up!

I've already replaced the cap (and the other Rifa cap on the mains input) with an equivalent modern part, I wonder if there are schematics for this PSU module around somewhere?

The power supply is based on the Computer Products / Artesyn NFS series. Circuit diagrams are hard to find. One unusual feature is the feedback loop and isolation. It is based on a small toroidial transformer with a iron dust or ferrite core. The core forms part of the drive circuit osciator and the feedback. It appears to use saturation of the core caused by current in the low voltage side winding to control the pulse width. Very clever design but  right PITA to troubleshoot I've had a couple, from HP8920A/B radio test sets with blown snubber RIFAs. This results in the MOSFET going short to the gate. That then literally blows up two or three resistors, a oscillator transistor and one of the windings of the feedback transformer. Re-winding the little transformer is possible but a bit of a pain.

Robert.

Good info!

My PSU seems to be working fine so far, I guess the dying Rifa luckily passed without causing any collateral damage.

Off-topic - Terra did you got it?

[TERRA Operative]

Yes! It arrived yesterday, but I got home late, so will have a play with it today.

Thanks a bunch!

[Black Phoenix]

Yes! It arrived yesterday, but I got home late, so will have a play with it today.

Thanks a bunch!

Anything you may need just ask.

[wolfy007]

Yes! It arrived yesterday, but I got home late, so will have a play with it today.

Thanks a bunch!

Welll thats sounding exciting!

[Wolfgang]

And first item on the agenda, replace the Rifa capacitors before they...

ZAP!

F**k that stinks! 


I just popped my Rifa cherry! I'm officially part of the club. 

Oh no,
That is NOT a normal RIFA use case. It's not an EMI filter. It's a snubber across the SMPSU MOSFET.  Often when they fail in this design of PSU they take out multiple components. This can include the feedback transformer (just visible in your photo) which is a special part.
If the unit was still working post RIFA failure don't run it until the snubber is replaced. Unlike the EMI filter caps running with this one failed can cause more damage. The same circuit is used in the HP 8920A/B radio test set and I've repaired a couple of them and they are a PITA to repair.
Robert.

Now THAT was a REAL snub 

[wkb]

Be careful with another fan: the MegaZoom ASICs run really hot and the airflow is not stellar (IMhO) at the best of times. In fact, quite a few of the IC's run hotter than I like.

I added glued-on heatsinks on the MegaZoom's in my 54641D.

Very nice scope family all in all. A bit quieter would be nice, and a colour screen. But hè.. it was a gift from my previous employer (i.e. saved by an alert colleague who knew about my TEA from the eWaste recycling) so I can and will not complain about price-performance 

Wilko

I received the GPIB module for my 54622D today, together with the original micro grabbers for the data cable that had previously been missing.
Also got myself a usb floppy drive and a cheap floppy to update the firmware. Worked out fine, even though I have to say the self-extracting *.exe files for the firmware and quick help (from Keysight’s website) seem quite sketchy from today’s stand point .

The scope is btw. also in an awesome state. Didn’t actually seem that great from the seller’s photos, but after a thorough cleaning it looks superb .

Edit: The only thing I’m now still waiting for is a quieter fan .

[Black Phoenix]

Yes! It arrived yesterday, but I got home late, so will have a play with it today.

Thanks a bunch!

Welll thats sounding exciting!

Naa, it is just a simple Fluke Clamp meter I got for him for parts. It have some problems as the function dial not working correctly and measures Amps incorrectly.

It is for parts for his own clampmeter who works perfectly well, since he needs keypads and screws. It was cheaper to source a used but with all parts needed in good condition than new parts directly from Fluke office.

Fluke asks for 150HKD for one screw...

[electronomicon]

Be careful with another fan: the MegaZoom ASICs run really hot and the airflow is not stellar (IMhO) at the best of times. In fact, quite a few of the IC's run hotter than I like.

I added glued-on heatsinks on the MegaZoom's in my 54641D.

Thanks for the insight! I took a suggestion from another thread in the forum, so I thought it should be fine. But I’ll inspect it a bit closer, maybe I’ll also try the additional heat sinks.
I have a simple IR thermometer somewhere to check the chip temperature … but where?

[med6753]

Finally found a Fluke 8800A for a reasonable price, and after minor repairs (though someone has been in there before me), its working and reading pretty much the right voltage. 
Still needs performance check and maybe calibration as I think resistance is reading a touch out of spec as may be AC voltage.
PS: also a bit more cleaning, I only wiped it down a bit.
PPS: That 4000uF 10V cap is reading 20uF, the two 220uF 10V caps read ~400uF, one of the 220uF 40V reads 300uF, the 50uF 50V read a not as horrible ~60uF, but ESR on all is not great, especially the 4000uF.

Welcome to 8800A ownership. If you haven't already done so change ALL the Philips crapacitors because they are, well, crap. I also recommend connecting both the sense and guard as shown for maximum accuracy. Calibration of this DMM can be a little tricky but careful adjustments can result in excellent accuracy. It compares pretty much right on to my bench reference hp 3456A.



I have 2 parts units in my stash so if you need an unobtainium part let me know.

[TERRA Operative]

If you want the current newest version of the Philips capacitors, Vishay now make them. Check Digikey/Mouser etc, they are sold there.

[Robert763]

Ooh, I'll check that! Thanks for the heads up!

I've already replaced the cap (and the other Rifa cap on the mains input) with an equivalent modern part, I wonder if there are schematics for this PSU module around somewhere?

The power supply is based on the Computer Products / Artesyn NFS series. Circuit diagrams are hard to find. One unusual feature is the feedback loop and isolation. It is based on a small toroidial transformer with a iron dust or ferrite core. The core forms part of the drive circuit osciator and the feedback. It appears to use saturation of the core caused by current in the low voltage side winding to control the pulse width. Very clever design but  right PITA to troubleshoot I've had a couple, from HP8920A/B radio test sets with blown snubber RIFAs. This results in the MOSFET going short to the gate. That then literally blows up two or three resistors, a oscillator transistor and one of the windings of the feedback transformer. Re-winding the little transformer is possible but a bit of a pain.

Robert.

Good info!

My PSU seems to be working fine so far, I guess the dying Rifa luckily passed without causing any collateral damage.

Indeed. I do't think the RIFA failure is the direct cause but without the snubber the MOSFET eventually dies and takes the rest with it.

[wkb]

Attached a picture of what my scope now looks like

Be careful with another fan: the MegaZoom ASICs run really hot and the airflow is not stellar (IMhO) at the best of times. In fact, quite a few of the IC's run hotter than I like.

I added glued-on heatsinks on the MegaZoom's in my 54641D.

Thanks for the insight! I took a suggestion from another thread in the forum, so I thought it should be fine. But I’ll inspect it a bit closer, maybe I’ll also try the additional heat sinks.
I have a simple IR thermometer somewhere to check the chip temperature … but where?

[wkb]

And should it ever display that crazy pattern: time to hunt for tin whiskers and resolder everything around the relays in the frontend circuits (incl. the BNC's). Probably due to that crap lead-free RoHS solder that was forced upon us 

[W6EL]

Found the photo of my HP 8647A RIFAs.

There were two of the usual gold RIFAs. I also replaced one blue plastic cap which had the RIFA brand name on it.

The prior owner, presumably the person that wrote "bad" on the back of the PSU shield and on the heat sink, replaced two transistors from the set of three against the heatsink. My photos aren't good enough to verify the reference designators.

I believe it was a Defpom video on this very model where I saw the RIFAs blow up and decided I better pull mine. Note that it is also worth changing out the IEC inlet as these are known to go too.



(Can you smell over the internet? I think so.)

[Robert763]

The blue one is probably OK. RIFA is OK as a brand, it's the late 20th century amber epoxy moulded self healing paper capacitors that are the problem.

[Robert763]

Did a bit more digging on this and found a patent that covers the basic design:
https://patents.google.com/patent/US4323961
Interstingly the snubber is not in the circuits but the power switch is a bipolar not MOSFET.

Also found part of the 8920A/B PSU
The snubber is C7 R4 CR2.  Note the 8920 PSU is significantly more complex because it will also run from 12-28V DC.

[srb1954]

The blue one is probably OK. RIFA is OK as a brand, it's the late 20th century amber epoxy moulded self healing paper capacitors that are the problem.

And early 21st century as well.

As a precaution I recently replaced the RIFA caps in my 2005 build 3458A and I found that there were already significant cracks in the epoxy encapsulation.

[factory]

Yes he needs a 3400A, preferably an early one to go with all the 1960s HP TE he's restored recently, I suspect the HP microfiche he has access to will reveal the info on the neons used.

I've still got to put together a Mouser list for the 03400-66512 board, the ground stand-off I'll have to make, couldn't see an off the shelf version long enough. The Molex test pins, I've salvaged some originals from the 180 series SA junk I bought from PP auctions (pile of units that had been used as spares by the last owner).
I've not ordered the boards yet, will probably get 5 or 10 made depending on price from JLC, is it worth going with the 2U ENIG?

David

At work there are always concerns with potential incompatibility with solder, HASL is recommended for high-rel. But I suspect it is fine of course.

Question, why are the traces seemingly constrained to right-angles? Is this to replicate the original artwork? Did you consider any upgrades as you went along?

HASL finish is solder based, the note about edge connectors with gold contacts and solder finish PCBs (from an ex-HP designer) was here (post #9); https://www.vintage-radio.net/forum/showthread.php?t=85375

The traces are very close to the original design, I was trying to replicate the artwork of the 1982/86 design, I haven't thought of doing any upgrades, I'm not a designer by trade, only a repair technician, I learnt KiCAD last year with the help & encouragement of the TEA regulars  , but I did do a little electronics CAD at college many many years ago.

I found some HP 5082-2800 (aka 1N5711) in the junk I bought from work and a few 1N825, no LT1012 though, but I do have the LT1013 dual version.
Seems in various places, people are using the LTC1052 in place of the ICL/TC7650 chopper op-amp, it's the same pinout, but near twice the price.

Re: ENIG finish, I was looking at some ex Marconi (made by Computer Measurements Corp.) counter boards earlier, the gold finish on those looks near exactly the same as the ENIG from JLC, i.e. dull rather than the shiny finish on the later HP boards.

David