Raiding a standard lab on surplus gear

[aronake]

I really wonder what the idea was behind the empty space between the A10 board and the A15 board. Sure, they already had the 5700a from factor of chassis they could use. But there is an extra edge connector where some kind of board would fit. On the other smaller side of A10 toward the front is where the wideband option is installed.

Any thoughts or ideas?

[aronake]

So now I have two fully working Fluke 5790a! Yay!

Challenge of course that they are not adjusted and calibrated.... So this opens up a new rabbit hole to get hold of a Fluke 792a (and a Fluke 5725a amplifier), get that properly calibrated so I then can adjust and calibrate the 5790as........ Or send in one of the 5790a and get that adjusted and calibrated.... Its 55 adjustment points and 127 verification points for standard calibration and around double for a service adjustment....

Anyone who have suggestion on something more budget friendly? Maybe some old thermal converters could work?

Even without adjustment and calibration is quite useful for relative measurements. I did DC adjustments on them, so even with the old AC flatness adjustments, which drift much less than the DC component, they should be pretty accurate.

[wkb]

Totally wild guess: maybe a board to calibrate or test the unit can be installed temporarily?

Wilko

[aronake]

I now got time to look at what is probably the most interesting piece in the haul, the Guildline 6675.

Slowly powering it up and there was a loud hum from the power transformer. And it pulled 200 Watt from the wall, rather than the 80 Watt or so its supposed to consume. Then some tantalums caught fire.... Clearly something did not seem right....

[aronake]

Did a full tantalum and electrolyte recap. Powered up slowly and hum and excessive power draw was still there. No smoke this time though, so some progress....

Disconnected did power down, disconnect power from one module at a time and slow power up to find out where the problem was. Showed out that with high voltage source not connected it started up fine with information on display. Inspecting the board I found this extremely suspiciously looking capacitor. It is used in the voltage multiplier for the high voltage output.

[aronake]

Swapped it out, and the 6675 powered up nicely with limited hum and a more normal 80 watt power draw.

Connected some crappy resistors to test. Did not want to start with a pair of ESI SR104 not knowing what the machine may throw out on its terminals.

[aronake]

And we got a reasonable measurement! Machine is alive!!!

The VFD a bit dim and worn out, but that is all fine. Ill keep eyes open for a better GU256x64-332 or make an OLED mod.

[aronake]

I will now do what the manual call "alignment process" rather than calibration process. Then some cleaning, make sure all is put nice in place and then some more serious measurements.

[trobbins]

Ooooh a 6675 - xclent to see you have jumped the first hurdle.   This is making me very jealous, as I haven't been able to progress the restoration of a 9930 so far.

[aronake]

Ooooh a 6675 - xclent to see you have jumped the first hurdle.   This is making me very jealous, as I haven't been able to progress the restoration of a 9930 so far.

Lets see how it goes with the final fixes. But it look promising. It is currently suffering from Dallas amnesia so some DS1225 are on their way.

I am considering if I should back up the eproms or not. They are socketed, so I do not see too big risk, but there is always some risk. The other option, hoping that some 30 year old eprom with content that likely is very difficult to get hold of should just continue to work seems to be a less good option.

Using it feels like getting hold of some mysterious ancient alien technology.

[guenthert]

Uh, while it is open on your bench, care to take a few pictures for those who don't have such opportunity?

[aronake]

Uh, while it is open on your bench, care to take a few pictures for those who don't have such opportunity?

Here is a dump of mixed photos. Seeing all these cables, I am quite impressed of myself being able to connect everything together.

I measured the cheap 10K ohm resistors with 3458a, and the ration came out to be close to 1.0043 so further confirms there is some meaningful measurements coming out of the machine.

[guenthert]

[..]

Here is a dump of mixed photos. Seeing all these cables, I am quite impressed of myself being able to connect everything together.

I measured the cheap 10K ohm resistors with 3458a, and the ration came out to be close to 1.0043 so further confirms there is some meaningful measurements coming out of the machine.

Thanks a bunch.  I realize it's additional work and there are other priorities.  I just like to marvel at those exquisitely designed instruments and wonder about the design decisions made.

Given that the 6675 is a DCC bridge, there ought to be a fancy transformer (with many connections) in there, no?

[aronake]

[..]

Here is a dump of mixed photos. Seeing all these cables, I am quite impressed of myself being able to connect everything together.

I measured the cheap 10K ohm resistors with 3458a, and the ration came out to be close to 1.0043 so further confirms there is some meaningful measurements coming out of the machine.

Thanks a bunch.  I realize it's additional work and there are other priorities.  I just like to marvel at those exquisitely designed instruments and wonder about the design decisions made.

Given that the 6675 is a DCC bridge, there ought to be a fancy transformer (with many connections) in there, no?

Absolutely no problem! Thanks for showing interest and asking!

The mystery transformer is a black heavy metal box sitting under the 40 or so read coto relays (1st and 6th photo). Then lots of cables going into it which can also be seen on the photos. I have not tried to screw that apart yet, but now you gave me some inspiration

There are some more photos in the Xdevs article:

https://xdevs.com/article/g6675a/

[aronake]

The last obvious fix on the Guildline 6675 was to bring its ability to remember things after being powered off.

At had "normal ram" backed up with Dallas DS1216. I hade these replaced with Dallas DS 1225.

[aronake]

After understanding a bit better now how the instrument works out, the battery backed up memory is rather unimportant. There is no calibration data of meaning saved anywhere. And the machine do not get adjusted, just "aligned" which is some adjustments on some potentiometers to bring certain voltages on the boards to measurements with quite wide tolerances.

I still have not gone though that but will do.

Focus now is testing. Verified so far that I consistently can do 0.1 PPM or better 10K ohm transfers. First measure resistor A vs B, then B vs A and compare ratios. 0.15 PPM is the verification test limit, so a pass there. Amazing for something that has not been adjusted, calibrated or "aligned" in probably more than 15 years. I will do 10x ratios, high voltage, low ohm test etc later.

Its a rather interesting and exotic machine.

[aronake]

The nanovoltmeter can be adjusted, and adjustment data for this is saved in a battery backed up memory on the nanovoltmeter control board. But this calibration data is not used for actual resistance transfer measurements. For resistance transfer only the linearity of the nanovoltmeter and ADC counts are used.

[aronake]

I am now experimenting with GPIB control of the 6675. Unfortunately it has an older implementation than 6675a so the commands listed in the 6675a volume II manual do not work. Anyone have seen a list of commands for this? Sample program? Or volume II of the manual. I have asked Guldline so lets see that they say. So far i got Volume I from them.

Next step would be to disassemble the EPROM program files to see what comes out there.

[aronake]

GPIB command overview solved. I copied the info in the CPU board Eprom and dumped to Claude for processing. Claude came back with a very comprehensive list of all commands. I showed out they are very similar or maybe same as for 6675A. Great use of AI. Took 2 minutes to process.

[Reemuson]

This is an incredible haul. What does one do with two 5700s?

Out of curiosity, how much was the hammer price for the two lots?