Fluke 5440B PSU Fault Check Guarded Power - Page 1
Forum section: electronics / repair

author: denimdragon
author_rank: Regular Contributor
timestamp: May 01, 2018, 03:13:16 am
content: I picked this up today and I hope someone can help me with this error. I'm going to start clearing out an area for disassembly in the meantime and check the voltages in the service manual (This thing is F#@%!! Heavy and Huge). Hopefully it's not too much of a rabbit hole. I'm good at tripping and falling down those for some reasonThanks in advance!

author: wn1fju
author_rank: Frequent Contributor
timestamp: May 01, 2018, 01:35:44 pm
content: The rabbit hole shouldn't be too big! My experience with fixing my 5440B is that everything is pretty straightforward. Just methodically trace your waythrough the circuit(s). Do the obvious visual/simple inspections first (like the 25+ fuses in it) and look for bulging electrolytics, etc. Also check that noneof the relays have fallen out of their sockets (two did on mine and wedged themselves into the motherboard).Once you get the P/S straightened out, run through all the internal tests (after the ovens have all warmed up). That should reveal any remaining problems.The 5440B is a fantastic piece and yours looks like it has a nice bright display. Enjoy!

author: denimdragon
author_rank: Regular Contributor
timestamp: May 02, 2018, 05:09:24 pm
content: Quote from: wn1fju on May 01, 2018, 01:35:44 pmThanks for the tips, it's greatly appreciated!I've checked the voltages on the A10, A17, and A19 PCA boards. The A10 PCA has zero volts on test points 12 and 13. Also I checked the A8 PCA and there was zero output on the A/D pins. I'm going to study the schematics and make sure my hunch is correct that the TP12 and TP13 pins on the A10 which should be +30V and -15V respectively, are the source for the A/D output.Here are the voltages I measured from the 3 PCAs:I also took a look at some of the components and did a partial microscopic visual inspection of the A10 with about approximately 50-60% coverage. I notice that someone has done some work on this unit in the past. (I'll post those after I figure out how I can insert a photo that's clickable to larger more detailed .jpg files on my server.)I found that the Hex inverter, Multivibrator, a couple of 1N4002 diodes, and 2 voltage regulators had flux and tamper evidence around the pads. Judging from the date codes on the ICs it looks like this was an early repair (Cerca 1987-ish). I also discovered a bad 1N4002 diode (CR5) which was conducting in both directions. I pulled it off the board for a more accurate evaluation. I also didn't have any 1N4002s in stock. I'll be looking into a closer evaluation of the failed component later today.

author: denimdragon
author_rank: Regular Contributor
timestamp: May 13, 2018, 04:05:39 am
content: I have found a few things that need replacing on these boards. The A5 Output/HV Control PCA has one crispy zener diode I need to replace and another one in an area that seems suspect. My question here is can these zeners be replaced with other zener diodes with the same values? The burnt zener is UZ8706 and the other is UZ8712. I have a NOS Motorola 1N4736A I want to use to replace the UZ8706 and the specs are very similar, but there are some differences. Can someone tell me if it's ok to use the 1N4736A as a replacement?I also found swollen caps on the A9 REF/DAC Analog PCA. I'm going to replace those as well and hope this will get rid of the fault. What I'm really concerned about is the crispy zener. I'll have to hunt down what caused the issue to see if I can fix that. I would hate for that to happen again and damage something else.I appreciate any help. The pictures below are of the zeners and also snippets from the datasheets to see the differences in the electrical characteristics.

author: denimdragon
author_rank: Regular Contributor
timestamp: June 07, 2018, 10:11:17 pm
content: These 6.8uf 35V elec caps were on the A9 REF/DAC Analog board and I'm looking to replace them. The "IC" branded ones are Illinois Capacitor I'm assuming and they had some other brand I've never heard of called "marom"? I'm looking to replace them but I'm not sure if ESR (low ESR or general purpose) is a factor. Also how much would it effect the machine if I used 50V instead of 35V. Can anyone chime in with some suggestions. Thanks!

author: wn1fju
author_rank: Frequent Contributor
timestamp: June 07, 2018, 11:12:00 pm
content: I would just go with good 105 deg rated general purpose, good quality name brand (Nichicon, Panasonic, etc.) electrolytics. And 50VDC isfine. It looks like these 6.8uF caps are just used as extra filtering on the various DC lines coming onto the board. You could probably omithalf of them and you wouldn't even notice! And the reason I'm suggesting 105 deg caps is because there is an oven nearby on the board.

author: denimdragon
author_rank: Regular Contributor
timestamp: June 08, 2018, 09:21:35 pm
content: Quote from: wn1fju on June 07, 2018, 11:12:00 pmGood to know I'm thinking correctly. I had decided on 105°C caps when I started removing them from the board due to the closeness to the oven. Thanks for your help. Now I can put the order in to Mouser. Over time, I'm going to recap the entire unit, but one board at a time. That way I can see the end result.Another question, other than a 3458A and a 732B, what can I use to verify these beast with?

author: TheSteve
author_rank: Unknown
timestamp: June 09, 2018, 01:07:41 am
content: I'm also working on a 5440B and that same 6.8 volt zener is crispy(along with the pcb around it). I suspect it is a design flaw more then anything. I don't think we're the first to experience the problem. I am upgrading mine to a 1 watt zener, but have been running the unit a full week with the crispy one in place. The burn occurred so long ago that the PCB doesn't even have a burnt smell anymore.These are amazing units to work on, a big heavy box of fun.

author: wn1fju
author_rank: Frequent Contributor
timestamp: June 09, 2018, 01:39:43 am
content: You asked, "other than a 3458A and a 732B, what can I use to verify this beast with?"That question is better addressed to the metrology forum where you are sure to get N opinions from N replies! It is far from trivial, sincethe word "verify" has all types of meanings, e.g., accuracy, linearity, drift, repeatability, etc.I don't have either a 3458A or 732B, but I have a slew of 6-1/2 digit DMMs and it was very easy with them to see that my 5440B was at first notacting up to par as it would drift almost 1 mV when set to zero and acted "differently" every time I turned it on. The problem was tracedto dirty relays and I eventually ended up replacing all of them!

author: denimdragon
author_rank: Regular Contributor
timestamp: June 09, 2018, 03:43:24 pm
content: Quote from: TheSteve on June 09, 2018, 01:07:41 amAnd it still works as designed with the crispy zener? Wow these things are amazing! Also, in the service manual it says that these are 1 watt zeners. Maybe we need something bigger. Keep me posted on the progress or else I'll bug you when I'm on TiNs site (if it's the same "The Steve")lol.Quote from: wn1fju on June 09, 2018, 01:39:43 amI'm glad you mentioned the Relays. I need to make sure to clean them once I replace any more bad components. I have a 3456A, and a 3457A meter that I can use for now. In particular, the 3456A (I love that machine). In the next month or so I hope to pick up another meter that's better than my 3456A. I'm currently waiting for my Mouser order to come in so I can get this show on the road.Thanks guys for all the input.

author: TheSteve
author_rank: Unknown
timestamp: June 13, 2018, 06:50:01 am
content: I have my 5440B working well now. Now that I've said that something else in it will probably fail.Anyway the 6.8 volt zener that has gone all crispy on both of our A6 boards should not have failed. It is across the 5 volt supply that powers the relays. There is little to no chance that the voltage was too high as the supply has a crowbar circuit that will fire and blow the fuse long before it gets to 6.8 volts. That leads me to believe the zener's have been weakened by the back EMF from the relays and eventually started failing or perhaps Fluke installed the wrong value from the factory. So after it burns and eventually fails open that is why the unit will keep operating just fine. I suspect mine has been that way for many years as the burnt board no longer had any smell too it. I have since cut out all of the burnt portions, ran 3 jumpers and added a new diode.The biggest pain has the been the relays. I opened each one and cleaned the contacts with 99% alcohol and then Deoxit D5. I also cleaned the sockets/pins with D5. After that the 5440B had a collection of faults. I ended up finding a few relays that had less then perfect contact(tested resistance of every single one, opened/closed etc). However the biggest problem was that one relay had stopped cycling properly, it was stuck internally. I suspect my problem was never dirty relays as the unit was so clean inside you could eat off of it. It was most likely a stuck relay all along. I got that relay unstuck and had been running the 5440B for a few days without any faults. Then tonight I had another fault - turned out a different relay had stuck in the exact same way. I am going to have nightmares about American Zetler relays!Anyway, if you think I can help at all feel free to drop by TiN's chat and we can work through the problems. There are others there that have also fixed a 5440B before so we'll have you covered pretty good.

author: denimdragon
author_rank: Regular Contributor
timestamp: June 14, 2018, 07:22:25 pm
content: Quote from: TheSteve on June 13, 2018, 06:50:01 amThat is awesome information! I'll be sure to focus on getting those relays spotless and making sure I clean the boards good. I'm taking my time with it and hope to have it done before the end of the month. It's amazing that these things are the tanks that they are. It sucks that most companies don't build with this type of quality anymore, but I guess for the price of the 5440B new, the quality is to be expected. I love the way the system is laid out as well. Very easy to understand for a rookie like me, once I got over the overwhelming amount of boards in it. I'm learning a lot about circuitry in general from this unit.

author: 99tito99
author_rank: Regular Contributor
timestamp: August 23, 2018, 04:05:24 am
content: Hi denimdragon:Your table as does the Fluke 'Table 3-4' shows the TP4 at +28.0, but the Fluke schematic 'Figure 7-18. A17 Outside Guard Regulator PCA' shows the TP4 on an UNREG +24 volt rail. Is this a typo in the table? This came to my attention when I tried to adjust R18 to get +28, but the pot bottomed at only +27.Cheers,Mark***********************PS: The TP4 on the board is labled +28.8. +28.0 or +24.0, what am I missing?

author: Scopetechniques
author_rank: Contributor
timestamp: January 05, 2019, 02:57:14 am
content: I was changing the 0.150 ohm resistor on A17 which had crept up to over 0.3 ohms and was causing a slew of problems.I replaced it with a new resistor from Digikey (P/N ALSR5J-.15-ND).I also noticed the same issue with TP4 on A17. The schematic shows that it should be 24V at TP4.However the checkout section says to adjust to 28V, but it will not go that high.I looked at the LM317HVK circuit and datasheet, with the two resistors and trimmer in that circuit the LM317HVK will not go to 28V.So I assume the 28V note should say 24V.--Victor

author: denimdragon
author_rank: Regular Contributor
timestamp: May 23, 2019, 12:50:33 pm
content: Just for the record, I never had time to finish this projectSchool has been consuming all me time. I decided to let this one go as bad as I wanted to repair it. If anyone is interested PM. I just listed it on ebay a couple of hours ago.

author: TheSteve
author_rank: Unknown
timestamp: May 23, 2019, 04:28:03 pm
content: Quote from: denimdragon on May 23, 2019, 12:50:33 pmSo what is the "little bit better" item you've replaced it with?

author: denimdragon
author_rank: Regular Contributor
timestamp: May 24, 2019, 02:53:58 pm
content: Quote from: TheSteve on May 23, 2019, 04:28:03 pmHopefully a 732A that works but it's not in stone yet. One of the local shops I do repairs for on the side are looking to upgrade to a new Fluke 732C? Not sure if this the right nomenclature but it's the newest standard/s and a new Calibrator. I usually get there old stuff pretty reasonably priced. However, now you are making me second guess myself.I wanted to keep my 5440 but school has been mauling me latelyand I can't stand to see it sit up and go to waste. I know I shouldn't be asking this, but what do you think? The 732A is better right??

author: TheSteve
author_rank: Unknown
timestamp: May 24, 2019, 04:13:23 pm
content: As a 10 volt (or 1.018) volt reference the 732A is better, but it does a lousy job of delivering other voltagesThe 732A should sit quietly and run 247. The 5440 is a very nice DC volts calibrator, not something you likely want to leave running 247. They both technically have similar internal references. The 5440B uses two of them in series. The 732A has one ref and a boost network to get to 10 volts.So in the end I guess it depends on what you're looking for.

author: Tony_G
author_rank: Super Contributor
timestamp: May 24, 2019, 04:54:12 pm
content: Quote from: wn1fju on June 09, 2018, 01:39:43 amOut of interest where did you get the replacements and, if I may, what did they cost you?I have 2 5440's (B & AF versions) and I need to replace the relays in them for the same reason you did.Thanks,TonyG

author: picburner
author_rank: Frequent Contributor
timestamp: May 24, 2019, 05:54:02 pm
content: I replaced only one relay in my F5440B with the original type (the AZ431-17-205) and it cost me a fortune: $95 + $40 shipping + customs fee.Replacing them all would be a very crazy expense!

author: TiN
author_rank: Super Contributor
timestamp: May 25, 2019, 10:28:20 pm
content: Who am I to say, but since you mentioned it, I would never let boxes like 5440B go, unless you really have an emergency. There are not much alternative (reasonably priced) options to get precise up to 1kV DC programmable source with good linearity. 732A is a support not, not a replacement for the calibrator. You cannot use 732A to calibrate DC function on any meter, except maybe 3458A.Another benefit of oldie moldie 5440B is that many volt-nuts here have them and can help with repairs/support if you need so. For example I even bought few 5440B boards (don't have 5440B) just for sake of taking magic parts out of them to do experiments. Relays that are on them (DC ref board assembly and reference string) are no use for me, so there are ways to get them if your unit need parts.And 732A can be a lengthy and deep rabbit hole on it's own like unit here, that had popcorn noise spikes on the output, which I don't like. Already spent dozen of evenings checking resistors, cleaning parts (oven assembly is PITA to get inside!) and ended up replacing SZA263 zener chip. Now it sits silly uncalibrated, as few hundreds more hours need to be spent to get it into shape...

author: denimdragon
author_rank: Regular Contributor
timestamp: May 26, 2019, 02:27:25 am
content: Quote from: TheSteve on May 24, 2019, 04:13:23 pmI knew I shouldn't have asked. It was already hard enough to list itQuote from: TiN on May 25, 2019, 10:28:20 pmWell it looks like it will have to sit until I make time for it. Thanks guys for wisdom in this area. I'm glad no one bought itIn fact, I'm going to start working on it again at the beginning of June. I'll have a few days I can free up then.

author: denimdragon
author_rank: Regular Contributor
timestamp: September 16, 2019, 05:27:07 pm
content: Here we go again...So, my 3456A started acting a bit weird with voltage readings off about -.150ish mV and I thought it might have been something I pressed in Math that did this, but I was unable to resolve the issue which means, either use my 3457A meter which is as slow as a snail, or fix the 3456A. I have exactly one week before I'm back in class full time so that means this week has to be productive in getting my lab together before school starts. Now that I have to repair "Big Shirley" (my pet name for my 3456A), I figured it's a good time to finally commit to fixing the 5440B for good. I can't afford to put it off any longer, as this situation has proved the need of the 5440B if I'm going to have any kind of semi-decent electronics lab and metrology lab. Procrastination bites me in the @$$ yet once againI have been working on the 5440B off and on so I have resolve the original "Check Guarded Power". What's crazy about this is that on the A12 Filter A Board CR10 and CR11 Rectifiers were missing! I replaced those then I got my -15V and +30V rails back. After that, I powered it up and a new error surfaced."Guard Communication - Fault Check Garbled Data"This error popped up so I went to the A14 Guard Crossing Board. I checked all the Optos and they were good, so I replaced the 4 electrolytic caps with new ones, replaced the board and fired it up. Guess what... Yet another error, but at least I'm making progress right?!"DAC Digital - Fault Check A to D"When this came up I got a bit worried, hoping that the DAC/ADC are ok. I removed the A8 DAC/REF Digital board and replaced the single electrolytic cap with a new one. Inserted the board back into the 5440B and received another error. I felt a little better since the DAC/ADC seemed not to be the problem."Inside Guard - Fault Check Guard CTRL Bus"And this is the current state of affairs. I removed the A8 DAC... Digital board again because this time I used the manual method of removing each board until the error no longer occurs as instructed by the service manual. I'm starting to think that I need to replace all the electrolytic caps in order to get it up an running. I was going to wait until a later date but it seems I don't have a choice if I want to rule that out as being the case. I've already cleaned the relays with card stock and deoxit as suggested here.Another interesting thing is when the DAC-Digital board is in, I lose my -15V and +30V on A10 board and actual the +30V goes to 8ish Volts and the -15V goes to -.284mV. When the DAC board is out, those voltage return to there normal value -15.011V and +28.9V. I assume this means that the problem is definitely on the DAC board but I'm not sure, and the issue with that is if a Logic IC is bad, how do I check it?Another point... When I had all the boards in and tested the +5LH voltage, it's a small - voltage (-100-200ish mV). I know this rail goes to the logic on the A8 board, but I'm wondering if there something along the path that shorted to ground. I'm just not sure what would be the next move other than replacing all the caps, which I will do anyway. Any help anyone?

author: dj831
author_rank: Regular Contributor
timestamp: March 25, 2020, 11:18:01 pm
content: Hidenimdragon, not sure if you had success in repairing your 5440B. I'm ending in repairing mine, bought 2.5 years ago - no time, but this is something I would have never let go. Issue of mine was just that .15R resistor on guard that was ... desoldered!BTW, I had weird issues like yours, after repairing my unit. When it was cold, I had all sorts of errors. There was even a weird noise like a quiet sounding buzzer. My 5440B had a bunch of these yellow Nichicon capacitors, but two had turned to brown on regulator board (I think that this calibrator ran for week/months or even years without being powered off...).I've replaced all these capacitors by +125°C on all boards (c.a. the same price than +105°C), and I even increased values (most if not all 22uF were replaced by 47uF - exact same footprint). Since, no more issues, calibrator runs perfectly even if cold (apart stability, of course). I've checked stability after several hours against a 8505 from eBay ($50) and @ +10V, there is a difference of 10ppm between both. And both are rock stable(of course, this is not a proof in itself).Note about relays: I had issues too with relays, especially with smallest ones (2 form C). I cleaned contacts without any product, apart with very soft sandpaper (grain of 5000). For other relays, including sanded ones (total of 25 IIRC), I made a small board with an NE556, one half operating @ c.a. 7Hz and the other half being a monostable for c.a. 2 minutes. A kind of self-cleaning. That trick worked like a charm (same trick used with attenuator boards of Tektro TDS 700 series).I've since dumped nearly all devices - PALs on display controller PCA are readable - and an interesting thing, my calibrator has software v2.1 (most 5440B I've seen are fitted with software v2.0). As I'm in Europe and have the habit of 6 and 9 with tails, I edited EPROM U61 to change display font (reason why I've always hated 4511's) I will make a separate post about repair and mods of my calibrator when everything is solved (the four remaining things: being able to read 68701, solving 2x20 VFD issue - mine is readable, but not new, replace both leaky output 1uF capacitors, and add four feet).

author: picburner
author_rank: Frequent Contributor
timestamp: March 26, 2020, 07:06:48 am
content: Here is the dump of U3 (MC68701L).If you can, post your firmware version 2.1 and the PAL dump on the KO4BB website (http://www.ko4bb.com/getsimple/index.php?id=manuals).I did it time ago but my 5440B firmware was the old 2.0 version.

author: dj831
author_rank: Regular Contributor
timestamp: March 26, 2020, 06:48:23 pm
content: Hipicburner, sure, I will do (very) shortly! And thanks for your file, but I'd like to compare it with my version (I suspect they are the same). Hence the question : how were you able to read that uC?My 844USB is not able at all to read Moto UCs, and my ALL-07 could, if only I had matching adapter (ADP-68701) - Matthieu Benoit has no schematics on that adapter, but he has a very old programmer that is able to do readings, a Stag PP39.Since I'm (a bit) stubborn, I wanna succeed in reading that @*$# processorThanks for your input

author: denimdragon
author_rank: Regular Contributor
timestamp: March 26, 2020, 07:54:32 pm
content: Quote from: dj831 on March 25, 2020, 11:18:01 pmThanks dj831! I haven't touch the 5440B since last year but I plan on getting it done now since I have a little free time. Hopefully this weekend I can get back to it especially since I have added an HP 34401A to my meter collection for a totally of 3, plus i want to recap my 3457A and 3456A meter so I'll need the calibrator to be up to spec before I start on those. I'm also looking forward to your thread on getting your 5440B up and running.

author: picburner
author_rank: Frequent Contributor
timestamp: March 27, 2020, 07:31:46 am
content: Quote from: dj831 on March 26, 2020, 06:48:23 pmHi,I have a ALL-07 too but I also missing the ADP-68701 adapter.However, I have a DATA/IO 3900 also which is able to read and program this device.

author: dj831
author_rank: Regular Contributor
timestamp: March 27, 2020, 11:08:30 pm
content: Hipicburner, thanks for the info! It seems also that the 2900 does the job too. Meantime, I found everything to build a 68701 reader. Hence, I read my 68701, and I compare to your source code. When done, I post all dumps onxdevs, including equations on the three PALs. When I'm able to get back to work (probably now in may, I guess), I have to scan my SM, since there are differences from known SM, and mine (for example, components list of memory board A15 refers to software 2.1 with modified Fluke references).Stay tuneddenimdragon: keep in mind that restoring a 5440B takes time and (a lot of) patience, it's hard to fix it in few hours, in-betweenBut you took the right decision to keep it, for sure! Reason why I use confinement time to fix mine. I will measure replaced capacitors and let you know in a next post.Happy fix

author: picburner
author_rank: Frequent Contributor
timestamp: May 12, 2020, 06:45:23 pm
content: Did you then manage to read the contents of the microcontroller and compare it with mine?

author: dj831
author_rank: Regular Contributor
timestamp: May 13, 2020, 08:12:52 pm
content: Hi, yes! 100% identicalSince Ed Oscarson (a very nice guy) was okay to give his source code, I was able to complete the 68701 reader/programmer. You have a picture of my PCB on Matthieu Benoit's website:http://matthieu.benoit.free.fr/6801.htm(Matthieu has to complete this page with schematics and PCB). This programmer is able to read both 68701 (2kb) or 68701U4 (4kb)For now, I'm working on 2x20 characters VFD replacement, and on a 'screen saver' that turns off +29V after keyboard inactivity. I will post firmware version 2.1 when xdevs website works (I had issues yesterday when browsing).

author: picburner
author_rank: Frequent Contributor
timestamp: May 13, 2020, 10:36:44 pm
content: QuoteSo here they made no changesQuoteIt is a good idea use a vfd "screen-saver" since in order to get the instrument at the best it must be left on for four hours at least before using it.So you save a little these precious VFDs.

author: dj831
author_rank: Regular Contributor
timestamp: May 15, 2020, 06:01:00 pm
content: Hipicburner, denimdragonet al., I've just uploaded minutes ago latest known firmware (v2.1) from my 5440B on Xdevs, including dumps of PALs. Memory dumps are exact copy of my 5440B, meaning that this upload does not include edited version of U61, where I changed font of numbers 6, 7 and 9 to match European fonts (although 7 is more Japanese than European)For those upgrading their 5440B, I'm really curious to know what is the difference between versions 2.0 and 2.1

author: MadTux
author_rank: Frequent Contributor
timestamp: May 16, 2020, 03:00:10 pm
content: One difference between FW2.0 and FW2.1 is max output current, at least on my 3 5440As.FW2.0 has 25mA limit, FW2.1 is 65mA. Apparently there is a resistor on output board, that can be changed, so a FW2.0 board can output 65mA with FW2.1https://emperoroftestequipment.weebly.com/(search for 5440A)Straight swap from FW2.0 to FW2.1 gives a output current limit eror

author: picburner
author_rank: Frequent Contributor
timestamp: May 16, 2020, 07:27:08 pm
content: In summary: changes to be made to use firmware 2.1 and increase the output current.In the old A4 PCA output board 5440A-1610original resistors:R7, R8: 80.6 ohm +-1% 500mW 100ppm (CMF651-2-1P80E6)new resistors:R7, R8: 52.3 ohm +-1% 500mW 100pmm (155069)But don't blame me if you fry your calibrator

author: dj831
author_rank: Regular Contributor
timestamp: May 16, 2020, 07:44:26 pm
content: HiMadTux, thanks alot for that explanation! Just FYI, I had relays issues too with mine, and I made a 'relay clicker' using a 556 to bounce relays @ c.a. 7 Hz for c.a. 2 minutes, worked like a charm!picburner, you were faster than meConfirmed minutes ago, R7 and R8 are 52.3Dale resistors. I don't know (yet) if firmware was pushed on xdevs, but if not, I edit what I've pushed to reflect these changes in attached text file.Edit: as per marking (T1) and dimensions, matches Vishay/Dale CMF65 series, 1W

author: picburner
author_rank: Frequent Contributor
timestamp: May 16, 2020, 08:50:05 pm
content: QuoteThe resistors are likely to be 1W, I trusted what was written in the service manual.QuoteI have also had problems with a relay (one 6-way). It took almost a minute to change state and because of this the instrument did not pass the self test.I bought an identical new one that cost me an arm and a leg.Then, calmly, I managed to repair the faulty one too.P.S. Yes, fw2.1 is on TiN's ftp site, I've already got it, thanks.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 23, 2023, 09:29:59 am
content: Quote from: MadTux on May 16, 2020, 03:00:10 pmHardware current protection is made on resistors R5, R3 and transistor Q1 and the same circuit in the second arm.Replacing the resistor from 80.6 to 52.3 ohms does not affect the ratings of this circuit. (I checked). This means that the protection is triggered at the same voltage drop across the current-measuring resistor.Those. 65 mA*52.3 Ohm should be equal to X mA*80.6 OhmThe current limit for younger models is 42 mA. And not 25 mA as indicated in the passport. Perhaps they played it safe by specifying a much lower output current. Or the limitation was software through software measurement voltage on current monitor.Since it can be difficult to obtain 52.3 Ohm resistors, you can turn an 80.6 Ohm resistor into a 52.3 Ohm resistor by connecting a 150 Ohm resistor (0.5W) in parallel with the 80.6 Ohm resistor. It's much easier to find.

author: denimdragon
author_rank: Regular Contributor
timestamp: April 02, 2024, 11:36:35 pm
content: So, I'm back at the 5440B again, but this time with a strong resolve. Itis needed for upcoming projects and I actually found a Cal lab that willcalibrate it for a decent price once I get it going.I was fighting the "PSU Fault Check Guarded Power" error. I replaced theU2 (LM317) and U3 (LM7915) on A10 board and that error went away.Now all my voltages are looking good again.I ran the analogue test and then recevied the "DAC DIGITAL FAULTCheck A TO D". I looked the fault up in the troubleshooting sectionof the manual and it say the the ADC failed. I changed out the ICL7109CPLwith a new one and still no love. So now, I'm not sure where to look. I'mgoing through the board now and studying the schematics. If any5440B/5442 owners have ran across this error, what did you do to resolve it?I'm studying the schematic now to get a better understanding of thecircuit. My next step is to check and see if I have some issues withthe logic side of the board. Dr. Frank mentioned that he thinks I havea digital problem and he nailed it. It would be nice if the good Dr. couldadvise as well.I have to get this done so Thanks in advance!

author: MegaVolt
author_rank: Frequent Contributor
timestamp: April 03, 2024, 08:59:32 am
content: Does the device output anything in normal operation? Can you set it to 10V?It's difficult to guess exactly how he tests the DAC. But since you stopped at the very first test, this means that the DAC may not work at all as it should.Perhaps you should check the optocouplers; there may be problems with them.

author: denimdragon
author_rank: Regular Contributor
timestamp: April 03, 2024, 05:07:56 pm
content: Quote from: MegaVolt on April 03, 2024, 08:59:32 amI suspect the optos myself and I will pull them for testing.The outputs voltages:1V = 12.63V10V= 12.42V100V= -32.12V1000V= -40.35Obviously the are way out. Notably the (-) Voltages.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: April 04, 2024, 09:54:31 am
content: Quote from: denimdragon on April 03, 2024, 05:07:56 pmTo begin with, it is worth considering the low-voltage ranges. A minus in high ranges may be caused by another malfunction.Once the device produces something, you can start monitoring with an oscilloscope where the signal becomes incorrect. The device's DAC is quite simple. These are two channels of PWM DAC. You need to check:1. The support voltage must be stable and in the region of 13..14 V2. Check the presence of PWM on the transistors of each of the two PWM DACs.3. Check the signal after the DAC.You will most likely find the problem at one of these steps.

author: denimdragon
author_rank: Regular Contributor
timestamp: April 04, 2024, 12:19:02 pm
content: Quote from: MegaVolt on April 04, 2024, 09:54:31 amI will check these locations today and report back withmy findings.