Repair story of a Datron 1061A

[capt bullshot]

Having acquired a Datron 1061A recently, I discovered a weird failure with this box: Measuring positive voltage, the reading jumps in increments of about 10 digits, not the expected 1 digit. Yesterday evening I hunted down the root cause and fixed it to an happy end.
Read the full (but short) story here: http://wunderkis.de/datron1061a/index.html

[capt bullshot]

So, took some time yesterday and made some picturs, added them now to the repair story. Should be somewhat more descriptive now:

http://wunderkis.de/datron1061a/index.html

[Zucca]

Thanks! I hope you will keep us up to date with your next repairs!

[capt bullshot]

After the first repair which resulted in replacing a 6N136, I discovered some linearity problems with the A/D conversion. This is now solved, the story is updated with some more troubleshooting inside this bag of tricks:
http://wunderkis.de/datron1061a/index.html

[Gyro]

Nice writeup. 

The 106x series was the first which used opto isolators rather than pulse transformers. It probably saved a bit of cost (they used a lot more when they introduced autocal). They probably didn't forsee the degrading CTR problem - many years out of warranty of course. It might be worth doing a wider scale replacement if you already have multiple degraded parts.

[capt bullshot]

Nice writeup. 

Thanks!

It might be worth doing a wider scale replacement if you already have multiple degraded parts.

There's an interesting detail on the 6N136: the selected (white) ones have the same date code, the degraded ones also have the same date code (but another than the selected one.). So this might be a suspectible lot while others are still OK. These are the only 6N136 at least on the analog board, there's a lot of these dual channels used in analogue mode. The parts list shows them as Fairchild FCD880 (quite a standard dual channel coupler), but the actually populated couplers bear a totally different marking and the color dot from the selection process. So as long as there are no obvious failures, I wouldn't replace them without knowing the selection criteria. I guess some channel matching and CTR range at a specified LED current would be the criterion.
Edit: Most of the FCD880 are used in digital mode, and do not look crucial to A/D timing, so these should be easy to replace. Only one in analogue mode (for input Ibias compensation), still have to check this one.

[Gyro]

Yes, the selected parts might be more of an issue - Datron were always big on part burn-in and selection (some of the opamps and fets in my meters look as if they let a kid loose with a full colour painting set!). It probably also means that the non-selected ones had more mediocre characteristics to start with - the 'leftovers'. As you say, there's no way of knowing what the selection criteria was (apart from guessing significance of Ib and TC on opamps etc), anything digital is fair game though.

[ThunderMink]

hello capt bullshot and great work on the 1061 i was wondering if you are able to read the eproms on your meter? i am in need of the software as my meter is acting really wierd and i would like to burn new eproms to test if it is a software issue (probably is) hangs up and the display goes nuts.

best regards

[capt bullshot]

Yes, I should be able to read them, if it works, I'll post the a link to the images here. Just wait for a few days so that I can find some time to do so.

[capt bullshot]

So, it's been done quicker than expected:
[removed, because the images were broken]

There's three .bin files, for the three EPROMs M18 (left), M30 (middle) and M35 (right).

I've noticed something strange while reading them: M18 reads like it is erased and nothing programmed (all 0xFF). So I tried to power up the unit without the M18 EPROM (since there's nothing inside). Anyway, the 1061A doesn't work if M18 isn't inserted into its socket, there's weird stuff (most segments on, some blinking) on the display. After re-inserting M18, I had a fail message and maybe lost cal data. I guess the CPU was running wild without M18 and overwriting random RAM cells. At least the 1061A passes the self-test again after doing the Input Zero run on all ranges, so there seems to be no damage but I've to check the calibration.

Edit: That's got a simple reason, apparently my programmer is defective, so don't use these images.
https://www.eevblog.com/forum/testgear/searching-for-datron-1061a-firmware/msg1740494/#msg1740494

[ThunderMink]

Thank you for the eprom dump

I will try to burn the images and test if it resolves the problem.

That was really wierd.. hopefully it did not screw up the calibration data.

best regards

[dacman]

hello capt bullshot and great work on the 1061 i was wondering if you are able to read the eproms on your meter? i am in need of the software as my meter is acting really wierd and i would like to burn new eproms to test if it is a software issue (probably is) hangs up and the display goes nuts.

best regards

The issue with the computer crashing is usually due to a bad contact on the digital board.  One issue with the Datron series is that the (DIP) ICs are in tin-plated sockets vice gold.  (They appeared to switch to gold-plated IC sockets once they were acquired by Wavetek.)  I'd clean all the IC contacts that are in sockets, at least on the digital PCB.  If you pull the CMOS memory, the software calibration would need to be performed.

[dacman]

My opto isolator story on the analog PCB is that M2 seems to only be required to work at initial power-on.  On at least two different units that were warmed-up in one location, then powered down and move and powered back on, they both initially detected the option boards but not when powered off and powered back up.  M2 had to cool back down awhile before it would work again, and I wondered if it was "selected" on purpose and I also wondered if those dots meant different degrees of degradation.  If different color dots could be put on ICs that are within the IC manufacturer's parameters, then the Datron repair manual would be incomplete.  Either the schematic would need to indicate that the part is selected, and why, or the parts list would need to.