Datron 1071 shows Error OL - Page 1
Forum section: electronics / testgear

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 30, 2014, 11:31:05 am
content: Hello,my Datron 1071 works fine and I was measuring 1V with my meter. But suddenly it shows "ERROR OL" even in the 1000V Range.I've tested a few things:The isolation amplifier looks fine. +/-40V are looking ok. I fed in a Signal an measure TL8 (isolation amp out). TL8 follows the input signal is was divided/multiplied (depending on the choosen range) as described in the service manual.I measured the +REF1, +REF2, -REF1 and -REF2 at the AD switching 4051 (M35). All of these reference voltages seems ok (6,3V and 0,39V)The test function stops at ERROR 5. This test tries to inject a test voltage and measures it back. I've measured the injected test voltage and it seems ok. I think this test fails because of the overflow state of the AD.The overflow error also stays in AC mode. I think the problem must be around the AD. So I measured the output signal of the switch (M35) and the output of the buffer behind the switch. Both signals are exact the same, so this stage should be ok too.I've attached the signals of the AD (yellow, TP4) and the buffer output (blue, TP5). For this measurements I connected my scope GND with the LO input and I applied 10V to HI in the 10V Range (which should be in middle of the AD range). A change in the input signal (at HI) changes the integrator output.I'm not sure about the integrator signal. Should it look like that?I hope anybody can decrypt my bad english and can give a hintThanksPhilipp

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 30, 2014, 08:52:12 pm
content: I've found out, that the null detector doesn't work like it should work. Without a null detection the integrator runs over 0V in the positive side (with an positive voltage applied to the input). At a certain time it looks like the controller switches the AD in the reset state (timer overflow?).Now, I'm thinking the signal from the integrator output I've posted before is not right. The integrator signal should not run "over" the 0V. I think this happens because the digital part of the dmm doesn't get a null signal. The optocoppler connection looks fine. I think the issue must be in the null detector.

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 30, 2014, 10:16:20 pm
content: I've found something strange or I should go to sleepI think the output of the LM311 should be inverted? The yellow signal is positive and the blue signal, too? How can that happen? Or am I wrong?PS: The blue probe is 10V/div not 1V/div

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 30, 2014, 11:43:30 pm
content: It seems to be wrong in the service manual. Pin 2 of the LM311 isn't the inverting input. In this case the circuit seems ok to me, but it doesn't fit to the description in the manual.

author: e61_phil
author_rank: Frequent Contributor
timestamp: April 01, 2014, 08:31:12 pm
content: The Datron 1071 is runningIt was a faulty optocoupler in the null detection.I hope this monolog thread can be usefull for somebody with the same problem.Anyone who is interested can read the whole repair story (but in german) onhttp://lowcurrent.wordpress.com/2014/03/31/datron-1071-zeigt-error-ol/

author: dml
author_rank: Regular Contributor
timestamp: August 08, 2018, 12:51:35 pm
content: Hi,While this appears to be an old topic, I'm encountering a similar problem now with a 1062 unit and this is one of the few live references to 'error 0L' I could find :-) This one doesn't seem to be covered in the service manual (or I'm not managing to find it).The link to your writeup here seems to be marked private on wordpress - is that intentional? I'm interested in following the repair. In any case there are good clues posted here I can probably use to narrow things down a bit.Thanks!

author: BNElecEng
author_rank: Regular Contributor
timestamp: August 08, 2018, 01:26:05 pm
content: Hi dml,Had something along the same lines recently with my 1071 and one of my 1061's which I managed to repair. I've got a 1061 with some weird leakage problem I'm currently trying to hunt down.Have you had any luck tracking the fault down to a specific board or circuit? I spent a good few hours on each machine just trying to work out where the fault began. Does the fault occur in a specific mode or range?

author: dml
author_rank: Regular Contributor
timestamp: August 08, 2018, 02:00:14 pm
content: Hi,A bit more poking around (I only obtained the unit this week) suggests there are multiple faults - the 'Error 0L' could just be a side effect. It produces this error occasionally on startup but more frequently just flickery garbage on the display.Strange that the error appears on a clear, stable display when it appears at all. In the 'flickery' state it looks like the VFD is not properly powered or is being updated too quickly - half the segments are dim or intermittent and the rest bright and unstable. Looks like the kind of thing you might expect from power issues.There are several faulty capacitors and a corroded looking LM309K regulator. I'll deal with that stuff first and see if the same error returns or something new and exciting happens instead.

author: dml
author_rank: Regular Contributor
timestamp: August 08, 2018, 03:31:32 pm
content: Well it appears 'OL' (I incorrectly wrote '0L') means 'output limits exceeded' on other Datron devices, so it probably has the same meaning here. It can refer to either voltage or current limits but more likely voltage in this case.I consistently saw this error (and no garbage) with power removed from the +/-15v rails. This was after discovering that part of the PSU wasn't working correctly. An under-powered section *might* be interpreted as a limits fault so it could easily be a side effect of that.Hopefully the affected circuits haven't become toast. The digital side seems ok (as far as I can tell anyway) and it does go through the display test.I'll hopefully know more once the psu is repaired and voltages checked etc.

author: e61_phil
author_rank: Frequent Contributor
timestamp: August 08, 2018, 06:41:14 pm
content: Hi,I closed the page because of the DSGVO.The optocoupler (M1) for the null signal from the ADC was broken in my 1071

author: capt bullshot
author_rank: Super Contributor
timestamp: August 08, 2018, 08:16:42 pm
content: Quote from: e61_phil on April 01, 2014, 08:31:12 pmPhotocouplers can cause interesting issues within these Datrons:http://wunderkis.de/datron1061a/

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2018, 08:35:22 pm
content: Yes, they should have stuck with the pulse transformers that they used in their earlier models, they never fail.

author: DC1MC
author_rank: Super Contributor
timestamp: August 08, 2018, 10:24:56 pm
content: The optos, tantalums and elcos arekryptonite for these instruments, I've had the same experience, plus the strange white dust corrosion. But once replaced they will be good for another 40 years.Cheers,DC1MC

author: dml
author_rank: Regular Contributor
timestamp: August 09, 2018, 09:57:01 am
content: Thanks for all the input. Plenty of stuff to look into. I'll report what I find.There are a lot of tantalums in there and few of them offer nice readings in-circuit so testing them means disturbing or removing them. I'll assume they're all going but will try to leave it until I run out of other stuff to check as it's going to be tedious and I'm sure most will test ok *after* they're out :-). I have removed a few electrolytics which tested good but will renew them anyway. Meanwhile I'm waiting for parts to turn up...One of the electrolytics had burst open but apparently didn't damage the board. There is a strange white powder on some surfaces and a greyish film on the back of the front panel board. The solder joints to the LM309 regulator fell off as soon as I removed the screws. I think some of the 'stuff' came from there. A few ICs were not fully inserted in their sockets.Apart from those things the unit seems to be in good shape and the nice big orange display seems to work well when the rest of it cooperates... it looks so much nicer than LEDs and easily readable from the other side of the room!

author: dml
author_rank: Regular Contributor
timestamp: August 10, 2018, 04:13:00 pm
content: Whatever was eating the solder joints on the LM309K has also done a good job of eating the aluminium heatsink next to it...It's crumbling away as white/grey powder - probably oxide. Does acid flux eat aluminium? As far as I can tell it's still busy too...The problem is I'm not sure if I can put this LM309 back because the stuff may have made it between the pin and the seal around it. I cleaned the pins with hot flux, solder and then acetone. It looks ok but still...If I replace it with a NOS device the low-ohms series resistor will need to be replaced as well. I checked the output from the original and it reads 5.12V with a very light load.Maybe it's best to put the old one back until the rest of the unit is working and consider replacing it later, making any necessary adjustments then?

author: dml
author_rank: Regular Contributor
timestamp: August 10, 2018, 04:40:32 pm
content: On second thoughts, the resistor isn't going back in. It's corroded and bulging at one end.My poor old DMM doesn't read 0.15R too easily so I'll just replace it. Which means I might as well replace the 309 at the same time.Seems like the problem didn't spread too far but will check the components nearby anyway.

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2018, 04:42:45 pm
content: That corrosion around the LM309 has been seen before - on a 1062! Take a look athttps://www.eevblog.com/forum/testgear/datron-1062/Reply #13 onwards I think.I think someone maybe used an incompatible (acid?) flux when fitting them - or maybe whatever they lubricated the rubber sleeves with, or leaching out of the rubber itself. It seems more than a coincidence.

author: dml
author_rank: Regular Contributor
timestamp: August 10, 2018, 04:47:52 pm
content: Thanks - this is actually a 1062. I may have hijacked this thread slightly towards the endbut I'll get back to the error OL soon hopefully!That last pic shows a similar hole chewed into the heatsink. The rest looks familiar too. Definitely not a coincidenceD.

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2018, 04:57:35 pm
content: I wonder if they were made in the same week, probably by the same person anyway. Whatever you do, wash the bits and replace that sleeving!

author: dml
author_rank: Regular Contributor
timestamp: August 22, 2018, 09:01:24 pm
content: So I rebuilt the corroded regulator sections of the power supply, recapped it, replaced tantalums and checked the test points to confirm voltages, no shorts etc. before reassembling and smoke-testing the thing.I was met with the familiar flickery, cycling garbage on the display and wisps of magic smoke from a NE5534 on one of the analog boards.'Great'I stripped it all down for another inspection. The supply still measures +5, +15, -15 and 180V at the test points when disconnected from the rest of the unit.Testing it with the damaged board removed but the other boards installed, all of the supply rails still read correctly - except the 5V rail which is wobbling around 2.5V under load.Testing the input to the 5V regulator (LM309K) shows a fairly steady 11V (on the DMM - not tried the scope yet), but is outputting 2.4-2.7V. The regulator doesn't get warm.I left it there for today.I figure the drop is probably a faulty LM309. It could be something loading down the 5V rail but it doesn't seem like the regulator is heating up at all. it should hit a current limit of 1.5A so nearly 13W going into the heatsink. That doesn't seem to be happening. If one of the rectifier diodes has gone, it might cause something like this but I would expect the 11V to drop in that case. I'll check it properly tomorrow.In my infinite wisdom I had put the original LM309 back in along with a new 0.15R resistor, after cleaning the pins from corrosion. I should have used a new one. I did test it before deciding to use it but without load.So I'll try a quick load test on the 5V rail then replace the 309 for a retest.No idea what happened with the opamp on the other board but its next to two tantalums which also got very warm. I'll need to come back to that mess later.

author: dml
author_rank: Regular Contributor
timestamp: August 23, 2018, 01:28:28 pm
content: And finally... back on topicThe LM309K was bad. It was dropping under load and causing the digital section to crash. Maybe because the corrosion had crept up the pins and got inside.So I replaced this, reassembled and the digital part is functioning again, well enough to report errors.Analog part is still toast. I think this Error OL will appear even with the analog sections completely un-powered - and so, not specific enough to diagnose anything - but will try to confirm next time.

author: dml
author_rank: Regular Contributor
timestamp: August 23, 2018, 03:14:52 pm
content: The smoking NE5534 was apparently caused by bad tantalum caps. Those and the IC have been replaced and no more fireworks.Still have the Error OL but no big surprise there.

author: DC1MC
author_rank: Super Contributor
timestamp: August 23, 2018, 05:47:52 pm
content: What happens if you press the TEST button ?Also you should remove all the subsytems connectors (R, AC, CC ...) and leave just the voltage (ADC).If you want to run first a test with the resistance measurement board connected, don't forget to switch on 2 wires, or the R test will fail.If the upper ADC board is bad and the test fails, it's about time to get into details, starting with the high-voltage converter and those 5 elcos there, they are most likely gone, mine were and I've had a similar corrosion (mine was some kind of an white dust, allover).Good luck,DC1MC

author: dml
author_rank: Regular Contributor
timestamp: August 24, 2018, 11:51:51 am
content: Quote from: DC1MC on August 23, 2018, 05:47:52 pmAfter a bit more messing around, the front panel is responding to some of the buttons (previously it wasn't) so I can run the TEST sequence now and it gives a bit more information including additional error codes, some numbers and at least one PASS result. It always begins with 'Error OL' on startup though, and ends with it.I'll spend some time with the service manual looking at the order & inputs for the tests next.Quote from: DC1MC on August 23, 2018, 05:47:52 pmI have all boards connnected currently, mainly to check component temperatures and shorted components. I'll start disconnecting things again for the next round of tests.Quote from: DC1MC on August 23, 2018, 05:47:52 pmOk, noted!Quote from: DC1MC on August 23, 2018, 05:47:52 pmI have replaced the 5 electrolytics and they were dry, reading high ohms. However I'm sure there are still other problems in this board. Will see what else I can find.There is one more problem with a socket or dry joint as the unit usually won't power up properly when upside down, display remains dark. Or it could be a problem with a relay contact. I have re-seated ICs on two of the boards but there are plenty I haven't touched yet.Quote from: DC1MC on August 23, 2018, 05:47:52 pmThanks!

author: dml
author_rank: Regular Contributor
timestamp: August 24, 2018, 04:36:30 pm
content: With the lower analog boards disconnected, this is the result on power up:- brief flash of what looks like a voltage reading on the display- Error OLpress - display test pattern sequence- Error 5press - PASSpress - Error OL'Error 5' is from 'DC isolator' tests in the voltage section. The other sections are not connected.The last result in the test sequence is 'PASS'. I think that corresponds to the corrupted NVRAM/SRAM check - which isn't too interesting.So the top analog board is faulty.With the other boards connected I got 'Error 6' as well, which is for the Ohms section. Seems like there is a lot of debugging ahead :-|

author: dml
author_rank: Regular Contributor
timestamp: August 24, 2018, 05:10:59 pm
content: Okaaaay... so I started swapping over some ICs near the section where the NE5534 failed, working outwards. However the unit would go dark on me as soon as I lay it face-up, where the ICs are accessible. I had to do the power-up tests standing it on edge (as seen in the last photo).This got old pretty fast so I started looking for this intermittent fault instead. It seemed like maybe it was a relay contact having mechanical issues as it would tend to work at one angle, but not at other angles.Pretty soon after starting this exercise - flipping the thing over and tapping it - the display went dark 100% of the time, at all angles.At this point I gave the thing a decent bump on the floor and it sprang to life.For the first time I didn't get an 'Error OL' but instead it immediately showed a fluctuating +/-0.00V reading. Hitting the TEST button yielded only PASS.Yay! So both the digital and DC sections appear to work - at some basic level at least. But there is a mechanical fault somewhere that I still need to track down. I can maybe do this via the test points.Not sure if I'll have the same luck with the other two boards but things are looking up

author: DC1MC
author_rank: Super Contributor
timestamp: August 24, 2018, 07:02:20 pm
content: Started with the inputs short circuited and all the other boards disconnected, it's now the sockets shit and optos dead or decalibrated. I've wirebrushed all my chips and replaced all the optos.Anyway, we see a bit of progress hereCheers,DC1MC

author: dml
author_rank: Regular Contributor
timestamp: August 25, 2018, 09:01:30 am
content: Quote from: DC1MC on August 24, 2018, 07:02:20 pmDid you see a change on replacing the optos? I'll try this soon but want to understand the schematic a bit better first for the sections that aren't working yet.I'm still chasing some problems which didn't narrow down to anything straightforward. Most of the tantalums and electrolytics are replaced except on the display panel and the AC board.I get an Error 7 from the AC board but the rest is now PASS including Ohms. The Ohms section actually seems to work more or less correctly.Always Error OL + HOLD on power-up.On testing, Volts section reports PASS but displays a random fluctuating reading in all ranges when used. Doesn't notice inputs. Not sure what's going on there yet.So I have working Ohms, a PASS on Volts but with unstable readings and an Error 7 from the AC board. Still some kind of progress though.

author: DC1MC
author_rank: Super Contributor
timestamp: August 25, 2018, 09:30:07 am
content: Quote from: dml on August 25, 2018, 09:01:30 amYeah, the lack of stability was what determined me to replace all the bloody optos, their current transfer ratio (CTR) decays over the time and this translates in the changing of digital signals delays, because the input signal slew rate is determined by the driving resistor and they were using "clever" techniques to get some delays between digital signals depending of drive current and the specific characteristic of that individual opto.Of course this means specially selected and paired optos (this why they are marked with those color dots) and when they decay the CTR is even stronger dependent of temperature and the fun starts.Basically, if the analogue stuff is correctly set according to the calibration procedure, the ADC is good for 7 1/2 in all the 1061 series as well, the only difference is how it is driven by the digital board and that un-funny unobtanium POS from Ferranto.One of my little projects is to decompile the software and fully replace the bloody digital part with a modern MCU board, the forrum post is around. It's a fun thing, but I don't see it getting too much traction, the 1061, 1061A and 1071 are becoming rare and not many people are willing to thinker with this stuff when they can buy an HP something, re-cap it and be done with it.But I find it fascinating.Cheers,DC1MC

author: Kleinstein
author_rank: Super Contributor
timestamp: August 25, 2018, 09:48:41 am
content: Quote from: dml on August 25, 2018, 09:01:30 amIf Ohms work correct, but voltage ready odd (e.g. like an open input), this points towards trouble with a relay in the Ohms section.

author: dml
author_rank: Regular Contributor
timestamp: August 29, 2018, 09:03:18 am
content: Quote from: DC1MC on August 25, 2018, 09:30:07 amSo it sounds like it's not just a case of replacing them with newer or faster ones - but matched to the original devices, which have decayed by now and the selection criteria isn't written down anywhereWhen I was looking at replacement optos I was wondering if a different device e.g. MCT61/62 with higher CTR would cover the selection criteria - but sounds like it would just screw up timing even more.I have two of these 1062 units - so if I could rig something to read out the CTR differences on each IC. That might show something about the selection criteria for each slot (or dot colour). Two samples isn't really enough to do it with any confidence but combining 2 units with the white/green/red dots (assuming all white dots mean roughly the same CTR) would maybe give enough info to get a clearer idea.Quote from: DC1MC on August 25, 2018, 09:30:07 amIf it were just one or two optos it might be better to use a different device and adjust the resistors to get the right behaviour. But there are lots of optos in there - many dual devices.Also, hand-selecting the 'right' values these days would probably be difficult - many components don't vary much within a production batch. I was hand-sifting some power transistors recently for a repair and they were all effectively identical.Quote from: DC1MC on August 25, 2018, 09:30:07 amWhich one is that?Quote from: DC1MC on August 25, 2018, 09:30:07 amI picked these up because I wanted something with good precision, not too expensive (and they weren't!) and with a lit display which I can read from a few feet away in crappy lighting conditions. So that means LEDs or a chunky VFD. No LCD stuff. I think these orange displays look much better and clearer than any of them. I was lucky to get two with low hours - one has some fogging behind the glass in places but is evenly bright. The other looks factory new.I went for two because I understood the faults could be severe and swaps would improve chances of getting one to work. I think it should be possible to get both working now - getting quite close to it. Unfortunately the issues seem to be similar in both so 'swaps' haven't been as revealing as I was hoping.Also I enjoy messing with 70s-80s thru-hole techParts which I can actually see & maintain without a microscope and don't lose in the carpet at a 50% success rate. So I don't mind if it takes me a while to bring them back to life.

author: dml
author_rank: Regular Contributor
timestamp: August 29, 2018, 09:14:18 am
content: Quote from: Kleinstein on August 25, 2018, 09:48:41 amI'm still trying to figure this one out - not had as much time on it recently as I hoped - but your suggestion sounds about right. Either a relay or a board connection fault somewhere.At least one issue with internal test failures was resolved by re-flowing the board interconnection pins around the frame. I had noticed various squeaking sound effects on lifting and moving the board, either PCBs rubbing on each other or pins rubbing in joints, with any light twisting force. After doing this on one of the units, those sounds are gone and one of the internal tests began to pass for the first time.So the ohms and volts tests pass on that unit now, but AC test fails. And volts still shows no correlation between the input, the range and displayed reading. Ohms readings look correct (although I tested it only briefly so far with a few values in a couple of ranges). All volts ranges show some fluctuating, different value. I'm wondering if half of this is due to someone trying to store calibration in the volts ranges with faults present between the boards and I'm seeing large offsets due to that...Both units I have boot up with Error OL always - this goes away in ohms mode so long as a resistance is present across the inputs. I'll need to spend some time studying the overload detection circuits to understand whats going on here.Anyway I'll investigate the relays next and see if that helps with volts mode.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 29, 2018, 04:37:37 pm
content: With the ohms option installed, the voltage input first goes to the ohms board and only from there to the terminals. So the fault is likely in the Ohms board, as the ohms reading (2 wire ?) seems to work.A calibration error (e.g. lost memory) would result in a more or less constant reading. An open input (e.g. failing relay) would result in a highly drifting voltage reading, especially after switching from ohms to volts.

author: dml
author_rank: Regular Contributor
timestamp: August 30, 2018, 09:01:02 am
content: Quote from: Kleinstein on August 29, 2018, 04:37:37 pmThis was my understanding but it is very helpful to have it confirmed, thanks.Quote from: Kleinstein on August 29, 2018, 04:37:37 pmRepeated power-on-off cycles caused the drifting voltage problem to disappear. Both units now read 0.00V with the inputs shorted. So a relay contact is probably involved. I will consider removing them and cleaning the contacts.Both units read zero volts on AUTO range with inputs shorted. The first unit with all suspicious components replaced (except for the AC board) settles to 0.0000mV dead-on and remains there.The second unit with only essential repairs (PSU + 6 electrolytics on analogue board) drifts around 0.00xxmV but doesn't settle well. Within 5 minutes the range is 0.0030mV +/-0.0020. After 30 minutes its more like 0.0030mV +/-0.0010.The first unit has a fault in the AC circuit, showing 'Error 7'. It always boots with 'Error OL'. I have mostly ignore it until now, focusing on DC Volts first.The second unit passes all internal tests but usually boots with a blank display, which sometimes recovers and switches into DC volts, or recovers with 'Error OL'. Other times it remains blank until power-cycled again. This could just be a power bypass issue one one of the digital boards or excessive ripple on one of the rails. The PSU does still need some attention as at least one of the caps is known to be dry.Overall, looking good. Will see if I can get the remaining problems with the AC board and the erratic bootups resolved.Figuring out the 'Error OL' problem might come last.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 30, 2018, 03:42:06 pm
content: One should be careful about cleaning the contacts. Some relays might have gold contacts with just a very thin layer that is easily damaged. Sometimes just some use is enough cleaning.

author: dml
author_rank: Regular Contributor
timestamp: August 30, 2018, 04:14:19 pm
content: Quote from: Kleinstein on August 30, 2018, 03:42:06 pmThen I'll stick with 'some use' for now and see if the problem recurs. I'll treat cleaning as a last resort. Maybe with alcohol on a lens cloth between the contacts.

author: dml
author_rank: Regular Contributor
timestamp: September 02, 2018, 10:30:44 am
content: So the latest on this is both units now report PASS for DC,Ohms,AC/RMS.I didn't do anything particularly relevant - was tracing differences around the AC board, found some small differences in one circuit near test points 7 & 9 - but nothing that led to a real problem. By the time I was finished with that, the 'Error 7' had disappeared. It hasn't returned.So it may have been caused by another relay contact and fixed by a lot of power cycling and turning the unit over.It has become clear that some of the self-test errors in these units can come from relay contacts or maybe solder joints if the thing has been sitting on a shelf for years, or had a rough journey with a courier. I would expect that from time to time but both of these units had at least two cases each of problems magically going away after some use.Both units still boot up with Error OL, which doesn't return while using it or running TEST, even if set back to the default range/mode manually. The Error OL can be cleared by simply pressing HOLD.No progress on understanding that one yet but will be looking into it now.

author: dml
author_rank: Regular Contributor
timestamp: September 04, 2018, 08:52:13 am
content: A quick update on the 'Error 7' - it returned after being powered off for a day. It cleared after being powered on for 15 mins or so.Looks like it is temperature related and affecting this AC board only (swapping the boards also clears the error when still cold). The measurement error in all modes is much higher when the unit is cold but settles to very low error after 30 minutes. Since the error seems to be in the AC board, it's probably not being caused by optocouplers. In any case I have seen the 'Error 7' from this unit both before and after these were replaced.I hadn't noticed the temperature influence before because it had not been left running long enough for the error to clear until other repairs had been done.I'd be interested to know if it's typical for these units to fail TEST early in the warmup period - or if TEST should always pass, from cold.There are still some other startup stability issues, sometimes causing the display to remain dark until the UI buttons are used, as if the software is already running but the display wasn't successfully enabled during startup. Will see if I can find out more about this one.

author: dml
author_rank: Regular Contributor
timestamp: September 10, 2018, 11:40:21 am
content: In the process of an experiment described here:https://www.eevblog.com/forum/repair/datron-1062-dmm/msg1812974/#msg1812974...I stumbled into the apparent cause of the 'Error OL', without doing any thinking. The real cause was found somewhere between the seat and the steering wheel.Disconnecting the IEEE board from the MPU board allows the unit to boot without the error. Reconnecting the IEEE board causes the error to return.Bearing in mind the fact both DMMs show this error - meaning both IEEE boards are behaving the same way - I figured this must be something really basic.I looked up the function of the DIP switches hanging off the back of the unit, linked to the IEEE board. These appear to configure the operating mode for a DMM as a standalone bench meter vs an automated systems unit. My dip switches were configured in systems mode, with a valid address. I changed this to 'talker only' and 'no address' (all switches = 1) and rebooted the unit. 'Error OL' has gone away.Hopefully this helps someone else who picked up a Datron 10xx recently, carried out the obvious repairs and still saw this confusing error... RTFM!