Druck Unomat TRX Repair - Page 1
Forum section: electronics / testgear

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 01, 2019, 11:40:34 am
content: I just picked up a Druck Unomat TRX calibrator on eBay for a good price but it's sold as-is, for parts or spares and says it "doesn't power up". I haven't got it yet but I bought it because I've been looking for one for a while and, in the pictures, this one looks to be in great condition (they usually look like someone dragged them through a minefield). I'm struggling to find any documentation on it (I'm away from home and the internet in this hotel is weird), has anyone got a manual or anything helpful?I've used a Unomat TRX II before and you had to charge it up before use; the TRX model I just bought doesn't seem to have a charger with it but I don't even know if it uses rechargeable batteries given my lack of a manual.Hoping this is going to be a reasonably simple fix; I'll let you know.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 07, 2019, 12:04:13 pm
content: Well the Druck TRX arrived today and it's not going to be very simple but, with some luck, I may win. This post shows views of the overall state; the outside looks OK but, as expected, there's corrosion around the battery terminals and some corrosion or something on some tracks around the edges of the PCB, seems it might have got damp at some time. I did a quick cleanup and conductivity tests on some of the dodgier looking areas and added solder to bridge poor areas and 1 piece of wire where the track was dead.The biggest issue is that the flat flex (conductive paint/ink) cable is snapped so no wonder it didn't power on. I tried to take the crimpex connectors off the old end of the cable but bending the cable-piercing tangs caused them to snap so reuse is a no-go; I found some 'CLINCHER' connectors on Mouser and ordered a 12-position, 0.1" one to try out; according to the datasheet for 'ink' (if that's what my cable is) you need part number 67516-712 but that's not available so I ordered a 67516-012LF which is for 'ordinary' (I guess copper) cable butthe datasheet shows a very slight variationin the piercing tangs between 'ink' and 'ordinary'The 2x20 LCD looks like it's not the original with a lump cut off the corner to make it fit, I can also see dark water? seepage areas around the edges which means the display is probably dud too but I do have one spare that's the same layout, the problem is that my new one has a backlight that makes it fatter than will fit inside the case; I do however have a nice OLED display that make fit and work, we'll see.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 07, 2019, 12:26:39 pm
content: So a few appeals for help here:1. Does anyone have a schematic or any info like a user manual?2. Am I on the right track to repair the FFC? From a quick peel back of the plastic and an attempt to solder to the tracks it was clear that's not going to work so my plan is to cut it back a bit and square it off and then use the 'CLINCHER' connector to connect to the end of the cable that goes to the keypad and then make a wire 0.1" jumper cable that goes from my Clincher to the 0.1" header on the main PCB.3. The LCD is almost certainly a 5V one that uses the standard HD44780 or ST7066U parallel one and I have the luxury of being able to plug in different ones to try, I included a picture below, can anyone ID it from the markings?4. What's the recommended treatment/chemicals for the battery connector corrosion?My overall plan is to:A. Fix the FFC and battery connectors and see if it powers up and check the power rails.B. If I get nothing (or messed up stuff) on the LCD, try a different LCDC. Get into the FUNctionality of the system (worried that the many Bourns multi-turn pots may have got wet but the insides look OK (extra pic below)

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 07, 2019, 01:47:05 pm
content: Hmmm, in trying to match up the display connectors, I just realized that the old display has only 14 pins but the 'replacement' I have has 16 and so does just about every 2x20 character, 116x37 mm display I can find. Fortunately there's a long distance (13 mm) between the bottom of the display PCB and the top of the header socket it plugs into so there's options for custom wiring harness as long as the new display emulates the driver on the old one. I'm running on faith but I'm pretty sure that, given the age of the Druck, it's almost certainly a HD44780 or ST7066U or clone

author: madires
author_rank: Super Contributor
timestamp: September 07, 2019, 02:07:34 pm
content: Yep, presumably HD44780. Pins 15 and 16 are for the backlight.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 07, 2019, 05:50:23 pm
content: I'm going to wait to make sure I can get the keypad connector fixed before ordering replacement displays but I've done some research. There's no backlight on the DruckTRX's LCD which means it's only 10 mm thick and virtually all the replacement's I've looked at so far are thicker and won't fit because they have backlights; the only ones I've found so far are the Lumex LCM-S02002DSR which is the perfect size but it's $20 and has no backlight and maybe the Microtips NMTC-S20200XRYHS-10 but there's no stock and I can't even find a datasheet.Switching up the display to OLED sounds easy in principle butthere's a timing issue using drivers that think they are running LCDsbecause the time between commands/data for LCDs is typically 35uS and for OLEDs it's 600 uS and there's no way that I'll be able to get the source code - heck, they even went to all the trouble of blanking out every chip with some sort of milky molecular acid. If/when I get it running withanydisplay, I'll scope the connections.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 12, 2019, 08:41:40 am
content: Well I fixed the keypad issue using the 'Clincher' connector (see photos). I also tapped out the keys with a meter, drew out the circuit for the keypad (it's a matrix), thus proving that it all seems viable. The resistance of the keys when closed is around 20 or 25but that's probably normal. Looking at the TRX II, it seems like they went away from this shitty ink-flex-PCB, it occurred to me that, if I were servicing a lot of these, a replacement keyboard PCB could be made with copper rather than ink tracks.I tested the display, it's dead. I ordered one that looks like the exact replacement (basic HD44780 no backlight LCD) plus I tested some of the corroded-looking electrolytic caps on the power PCB and a couple were bad so I've ordered replacements for them too.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 12, 2019, 10:53:08 pm
content: The new electrolytic Caps and LCD display arrived today and I got them all fitted. The good news is that it now powers up, the display comes on, and it performs a self test; the bad news is that there's a "MALFUNCTION" message followed by ERRROR NCTION! message (whatever that means). I measured the +5V to the display and it was 5.299 which is too high (higher than the recommended max for 7400 series ICs whoch there is at least one of on the PCBs.Back to my original request; does anyone have any information, user manuals, service manuals, schematics, etc that they could share with me? It would be great to even know what that error message means.I can try to reverse engineer this but the fact that all the chips are covered in white cover up is going to make it really difficult; surely someone has been down this road before?

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 13, 2019, 12:01:06 am
content: I found the user manual online and there's a bit on page 56 that explains how to press 9 during self diagnosis which will show test data plus there's some outline pictures of the PCBs specifying what the various pots control so I can try that tomorrow but an actual service manual or at least the schematics for each PCB would be exactly what I need and they don't seem to exist I have some very dodgy-looking red board-board connectors - the contacts inside some of them are green and corroded. I was worried that I would not be able to find replacements for them but now I find that they are available and in stock with Digikey at about 10 cents per pin; they are called Micro MaTch and are 1.27 mm pitch. I'm going to test the resistance from board to board through these connectors tomorrow and order replacements as neededThe user manual also has a big list of test points and what pot you have to turn to calibrate so that is looking promising if I can get the system to pass the self-test stage.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 13, 2019, 01:05:38 pm
content: Update...I tested the Micro-MaTch conectors and even the dodgy-looking ones had good connections; I'm going to replace one pair but I don't think that's the issue. In poking around, I found an open circuit track that I repaired but the self test still fails. I was able to get the extra info by pressing '9' and it told me that the 0 volts is too high so next I'm going to try to run the calibration routine that starts on page 48 of the user manual, maybe someone tried to fix it before and messed with all the pots and screwed up the calibration? There's a big pot that does the LCD contrast and that worked perfectly so I'm hopeful that the Bournes multi-turn pots are OK too.This is way more involved that I wanted it to be but it's become a bit of a challenge for me.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 13, 2019, 03:34:03 pm
content: Ohhh, now I'm getting somewhereI made a keypad to test with the lid off (see picture, I know, I'm a masochist!) and did the press 9 thing while it's self-testing and I get the promised parameter test results. The mA input zero is supposed to be <200 and it's 371 so the next logical step is Calibration. I started trying to do a Cal and realized that there's a set of extension cables that allow the power PCB to be separated from the analog PCB underneath it and, unless you do this, you can't get at some of the pots to adjust - I looked online for the part numbers but, as everything else with this Druck, they are unobtanium. All that's needed is a set of IDC Micro-MaTch plug sockets for the 4 and 10 pin Micro-MaTch connectors on the Power PCB plus some ribbon cable, I'm going to order them along with the replacement for the dodgy-looking one mentioned previously.What I found was that, by using the 9 option, I eventually ended up in the normal working menu system (except there was the word 'ERROR' on the bottom left of the LCD) and I could then set the required outputs for the Cal procedure.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 16, 2019, 09:59:01 pm
content: Well the Micro-MaTch mezzanine connectors arrived today and I replaced the most dodgy-looking pair (which were 10 pin), cleaned up the PCB and fitted the new connectors. Then I made unobtanium extension cables that allow the power PCB to be connected but with access possible to the analogue PCB pots. 1 pot tweak later and she passed self test with a mA input zero at 002 so the display runs up and shows the expected screen.So I'll do a full calibration tomorrow on my calibrated Keysight 34461A meter and see if I can get it all back together and runningI'll post pictures tomorrow.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 17, 2019, 06:45:19 pm
content: In my prep today, I found another bad track on the PCB where the track is supposed to come from one of the pads where I replaced the mezzanine connector; I fixed itWell, not so fast! I got to stage 4 of the cal which is 'zero F' and I can't get the voltage down under 240 mV when it's supposed to be zero (the first 3 I got down to 1 or 2 uV! Plus, it keeps bombing out and telling me to replace batteries when I'm running off a bench PSU, I tried upping the PSU voltage from 6.3 to 7 but it was the same so I suspect a bad connection. Now I'm tapping through the power leads from the battery bay and through the myriad of tracks and mezzanine connectors that eventually get it to the processor board.I snagged another TRX for parts or repair today for a great price, it looks the same as the first one but it's black and is the TRX-IS model which is intrinsically safe; it has a "MALFUNCTION!" caption on the display. I must be a glutton for punishment.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 17, 2019, 09:14:00 pm
content: I guess that having a second unit may help me make a side by side comparison but it sure would be good to have a schematic! I think the chips have had their marking ground off with a Dremel so I can't even reverse engineer the schematic from the PCB. If I was REALLY lucky, the second unit won't have the chip markings ground off.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 20, 2019, 11:57:39 pm
content: Well I hate to say it for fear of jinxing myself but it seems that the second unit is a winner. I took it apart and all looked good so I put it back together, powered it up and it passed self-checks, and I've had it on my bench all day running with volts and milliamps outputs, no error messages, just normal behavior and the measured outputs are close to what I dialed in

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: September 23, 2019, 09:20:14 am
content: Shit. It looks like I did jinx myself; the second unit has bad power rails, there are 3 boost converters and 2 of them (+15 and +25) have no output even though it passed the self-test, I checked the electrolytic caps and half of them seem bad. Next I put my repaired power board into the second unit and it ran but I haven't proved that everything is working yet. Now that I have 2 units, it seems I'm 'lucky' that the first one has a power PCB that does not have the chip markings ground off and those converters are available from Digikey for 60 cents each; I tested that power was being delivered to them but no activity was on their switching output so I'm ordering replacement ICs. I've been reverse-engineering the schematic for the Power PCB and am making slow progress; there's this convoluted path for the battery that sends a live signal through 2 sets of mezzanine connectors, PSU>ANALOG>CPU which then looks for a ground on the  button and sends that back CPU>ANALOG>PSU to a CMOS NAND gate to detect and latch the power on state. An LM317 then kicks on and triggers a PNP pass transistor to feed all the other power circuits.Does anyone else on this Test Equipment forum even have a Druck TRX? If so, please feel free to chip in on this thread; I feel like I'm the only person in the Galaxy that's interested in it.I toyed with the idea of asking GE (who bought Druck a while back) if they would provide a service manual or a BOM for the PCBs but I think it much more likely that one exists somewhere out there from an authorized repair agent.I did findthis company in Indiawho talk about how they've reverse-engineered the TRX info, maybe I could reach out to them?

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: May 10, 2020, 05:58:35 pm
content: I've been asked about this Druck by another eevBlog member so attached is a hand-drawn picture of the high level power supply wiring looking into the back of a case with all PCBs removed. The batteries are 4 x D cell and can be rechargeable in which case, an internal link is moved - see picture. The 3 pin connector at the rear brings in approx +ve (positive) 6V on both outer pins, center is ground. One +ve supply is fed through to the battery through the link and the other goes straight to the power connector on the rear (power) PCB. Both the battery and any external +ve supply feed through diodes to provide polarity protection and prevent backflow between the 2 supplies. I've been using a 6V bench power supply and a spare Micro-MaTch connector. The most current I've seen pulled from this supply is about 400 mA and typically it's 220 mA.

author: ChrissyG
author_rank: Newbie
timestamp: May 11, 2020, 07:49:26 am
content: Thanks Gandalf_SrThat'll be me asking for help with my unit. My father snagged me this TRX II iS when a neighbour mentioned the electricity company were having a test equipment cull and the workforce might like to wander passed the skip on their way home. It looks unused and was in its case with manual and accessories but missing the 3 terminal power supply hence my contacting Gandalf_Sr for advice. The good news is that with 6v on both outer pins the unit powers up and even shows the correct date! I will do some further tests and try to fix the first issue - poor contrast after the unit shows its start screen. This is hopefully a bad user setting as the contrast returns immediately when the unit is reset.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: May 11, 2020, 08:42:06 am
content: ChrissyG,If the setup is similar for the TRX II as it is for the TRX (I suspect it is), then one of the 6V pins sends power to the power PCB (the first one you see when you take the back off) and the other 6V pin feeds power to the batteries for recharging purposes (so be careful in terms of current limits) on the battery feed pin. I once had a bad battery that I fed 0.5A to for about 30 minutes before it exploded! Fortunately nobody was harmed.I used to have access to a TRX II at my former workplace and I recall that the TRX II LCD was never very good contrast-wise.

author: ChrissyG
author_rank: Newbie
timestamp: May 11, 2020, 09:51:37 am
content: On first inspection it all seems to work other than the batteries that are completely dead. The charging circuit is drawing 250mA at 6v which is much greater than it should be. In the the TRX-II iS the batteries are potted into the rear section of the instrument case and there is some circuitry potted in there with them. 6 cells in all presumably wired in series, a power diode, transistor and chunky resistors. Further tested showed the instrument would in fact function without the battery connected. The battery pack connects with a four wire connection. I was hoping this was just power and temperature but I fear it's more complex than that. I have the option to live without battery power or try to cut out the battery compartment from the back panel and either replace the cells in the existing circuit or remove the recharging functionality and insert a battery box.The calibration on the instrument is 2007 as is the manufacturing date so I'm hoping it's one of those never used "backup" units like those you get from government surplus sometimes.The contrast is adjustable from the front panel I was just too stupid to get the intuitive buttons. Nothing in the manual about it because it is obvious.I like Druck products and have used a DPI 880 at work for 9 years or so. Talking to the company can be difficult but they were still in Derby UK when I last had a frustrating chat with them. GE are very protective of their IP.Volts, Amps and Ohms all seem to work.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: May 11, 2020, 05:00:00 pm
content: Glad you seem to have it working, I think the idea of cutting open the battery pack and replacing the cells seems like a good one. My Druck TRXs are in way worse shape than your TRX II by the look of it; mine look like they were fished out of a lagoon in Florida!Not a bad find for a dumpster dive!

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: May 12, 2020, 12:20:01 am
content: Well ChrissyG's prompting made me dust of the first TRX I got, the non-IS one; remember I previously went through it, changed 20ish electrolytic Caps, changed several pairs of Micro MaTch connectors, repaired several places where the PCB tracks had been corroded away, replaced the DIP keyboard connector with a new one that connected to the weird paint-like flat flex cable, and fitted a new LCD.Today I was able to run through the whole calibration routine and get nuts on in most places and within 1 or 2% in others. Then I reassembled the entire unit and it ran properly with the main keypad working properly and outputs within 1% of the requested values. If I go back over it, I think I'll concentrate on the power supply voltages e.g. the 5V rail is almost 5.3V which is slightly too high.Quite satisfying

author: Vasily_A
author_rank: Newbie
timestamp: May 15, 2021, 02:53:10 pm
content: Hello!I bought a faulty TRX-IS calibrator, there are two problems immediately noticeable:Power supply + 5V repeats power supply voltage on the battery, it worries me.The information in the ROM is corrupted, reading on the programmer gives 350-400 bytes, which differ with each read.Request: please read the ROM (dip28 fm27c256q or any xx27c256) of your device on the programmer, I will try to write the read data into my device.

author: AllSystemsMalfunction
author_rank: Newbie
timestamp: July 12, 2021, 07:27:15 pm
content: Does anyone have a firmware dump for the calibrator? I got one, but saw an EPROM chip - they aren't so reliable - so if there're is a backup - can i get it for my archive? if not - i'll try to dump it next week... better not bricking device along the way...

author: Vasily_A
author_rank: Newbie
timestamp: July 12, 2021, 08:01:56 pm
content: I'm really looking forward to this firmware, I want to revive the faulty device.if the device works, I plan to put several 18650 batteries in it with USB charging.

author: AllSystemsMalfunction
author_rank: Newbie
timestamp: July 16, 2021, 01:48:29 pm
content: So, finally i've dumped the firmwarefm27c256 - trx-r - 0x0034 8272 - checksum