1984 power supply repair - Page 1
Forum section: electronics / repair

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 01:46:22 pm
content: I'm trying to repair this power supply from an old 1984 computer it seems to not give enough power on its output.Its a 36v-5v DC-DC power supply branded ASTEC, there was a metal plate screwed to the back of the board to protect the solder joints from the metal case of the computer and on it it says ASTEC AA7281D (think the D is a rev letter as on another one of these power supplies it says AA7281 rev <letter>) 65-00029.When it is in the computer its 5v output reads only 0.5v. When out of the machine hooked up to 36v and nothing on the 5v output it reads about 5.8v.Nothing on the board seems obviously bad. The electrolytes seem good and everything else seems ok. Nothing obviously wrong.Any ideas as to what may be wrong?

author: dr.diesel
author_rank: Super Contributor
timestamp: August 18, 2013, 01:53:54 pm
content: Somebody stole R28! Normal to see unpopulated parts, a bit unusual to see snipped off ones!Anyway, you can verify the 5v rail isn't being shorted by the computer? Or perhaps can you load it while out of the PC and see what happens?

author: JoeO
author_rank: Frequent Contributor
timestamp: August 18, 2013, 01:54:44 pm
content: Capacitors - If you have an ESR meter, use it on the largest capacitors. If not, just replace the largest capacitors.It is 29 years old. The capacitors are probably "dodgy".

author: Tita
author_rank: Contributor
timestamp: August 18, 2013, 01:55:37 pm
content: Switch mode power supply repair video:View the entered video if you want to learn something! O0

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 02:03:30 pm
content: dr.diesel:I can verify the machine isn't shorting it. I have two of these computers (1984 Burroughs B25s) and I put the supply from one of them into the one with the bad supply and it worked fine. So obviously it is the supply itself.JoeO:I do not have an ESR meter. Guess I should get one if I plan on doing more electronics in the future. Really all I have to test at the moment is a multimeter. I looked up and some people have said you can test the caps by using the resistance mode of a multimeter? Anyway I guess I could replace them although to the fact that they are dodgy, yes they are nearly 30 years old yet I have 3 more of these power supply boards with original caps that say otherwise to being dodgy. (3 more because I have two of the computers and each computer requires two of the power boards)Tita:Thanks for the video.I guess I know what I shall be watching for the next hour!

author: dr.diesel
author_rank: Super Contributor
timestamp: August 18, 2013, 02:25:50 pm
content: Quote from: connorwk on August 18, 2013, 02:03:30 pmYou can get an idea, but nothing more unless you want to calc it, by knowing the meter source current etc. If you remove the caps from the board and test their resistance it should read a dead short and rise to infinity/open. How quickly it goes from short to open depends on the meter and size of the cap.Make sure they are fully discharged before removal/testing.

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 03:03:32 pm
content: I removed the two right most big electrolytes the left blue one went up in resistance from short so I assume its good the other bigger black cap went from short up but then I retested it and it was open. So I guess that cap is bad. I will replace it and try it I guess.

author: dr.diesel
author_rank: Super Contributor
timestamp: August 18, 2013, 03:11:01 pm
content: If you didn't short it back out the retest would still show open.Make sure it's completely discharged before each test.

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 03:17:15 pm
content: Silly me your right it is fine then. I guess I will check the smaller caps then and see if they are good.If its none of the electrolytes then I am unsure of where to go next.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: August 18, 2013, 03:32:29 pm
content: The solder doesnt look good in or around the capacitor thats just below IC1 (LM393P comparator) .Its worth replacing all the caps if you can and take out LM393P and clean its legs up .

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 04:29:01 pm
content: I took out all the caps they all seemed fine.I replaced the one cap under the lm393p chip since under it was a bit corroded.Unsoldered, cleaned the pins, and resoldered the lm393p and still it gives the same results. I would replace the caps but I do not have a good supply of caps I will need to buy a bunch later on but for now I don't have them to replace unless I used other values, but as I said they all seemed to test fine.I'm assuming its going to be a transmitter next then? maybe a diode? I guess I will have to unsolder them all and test them.I do have two of these boards so what I did before all this was go around just testing resistance between a bunch of different points around the board and compared it to the same points on another working board and everything seemed fine. I know that's not the proper way to test but I figured of something was way off I could know that somethings connected to those points where wrong.I'm not the best at repairing and testing electronics thus posting it here in the beginners, so thanks for all the much needed help.

author: Paul Price
author_rank: Super Contributor
timestamp: August 18, 2013, 04:39:17 pm
content: From the odd angle of the yellow transformer, it looks its been physically damaged.

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 04:57:00 pm
content: I don't think so the holes on the board are at a bit of an angle and on the other power boards it is angled as well but not as much.Looking at it all that's actually slanted is the ferroid core, like I said the plastic holder of the wire is slightly slanted because the holes in the board for it aren't square.But I don't think it is damaged the other ones look the same and they work fine.Probably just an 80's design thing.

author: JoeO
author_rank: Frequent Contributor
timestamp: August 18, 2013, 04:58:15 pm
content: Try moving the caps from the good supply to the bad one, if you feel confident enough in your soldering abilities.

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 05:19:33 pm
content: Hmm I guess I could do that.I guess capacitors would cause me not to get enough power out of the board?I'm sorry for my ignorance of electronics at the moment but I just don't understand how bad caps would cause just a power drop and not cause it to fail all together.Like I said the only problem is its not supplying enough power as I get 5.8v when not hooked up to the computer but only 0.5v when it is in the computer trying to power it.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: August 18, 2013, 07:20:36 pm
content: Its a good idea to try the caps from the good board , try the big caps first,then the caps at C20 and C21 .

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 07:53:47 pm
content: I did every electrolytic capacitor on the board and those two ceramics you said. still doesn't work.So no its not the 30 year old electrolytes causing the problems or those two ceramics.

author: Paul Price
author_rank: Super Contributor
timestamp: August 18, 2013, 08:37:24 pm
content: If you are getting almost no voltage out of this troubled power supply, the reason is not likely to be a capacitor, something more like a bad connection, shorted diode or transistor or bad IC or even a turn on/turn off part of the power supply circuit.There is a myth that all power supply trouble is caused by capacitors, but a good deal of is.If you follow some of this advice given here you will waste hours and money replacing good capacitors or else swapping capacitors(totally ridiculous! advice).If a capacitor dome top is flat and there is no sign of leakage of electrolyte, the cap is probably ok. If you test all the capacitors, in circuit with an ohmmeter, and see any indication the capacitor is charging, the caps are probably OK. Capacitors can be fine even after 36 years, especially if this device has not used much during this long period. Let an oscilloscope tell you if a cap is good or bad.if an ohmmeter measurement or an oscilloscope reading or even an AC DVM reading gives me reason to suspect a capacitor, I usually "bridge" a new capacitor across a a suspected capacitor (or even bridge several suspected caps at once) to troubleshoot.If I can easily doe this, I sometimes disconnect just one lead of a capacitor, leaving the other soldered, to apply a ohmmeter test, in the case I suspect a leakage current through the capacitor or just to see if it will charge, in the instances where coupling capacitors could be causing problems. For bypass filter capacitors, bridging and ohmmeter measurements in circuit is all that is needed to check the capacitor.I've been repairing electronic devices for a zillions years and have never needed or used an ESR meter, really not needed. If you suspect a capacitor is open or has an high ESR, simply bridge it with a capacitor of a similar or a somewhat larger value to see if you can notice a change in operation. Use an oscilloscope or DVM to measure noise voltage across a suspected capacitor, even a AC DVM can be well used to detect excess AC across an electrolytic capacitor.Try to ohmmeter test all the diodes, zeners, transistors, regulator chips and/or MOSFET. etc. for shorted or open junctions.The best tool for this troubleshooting job after resistance checks is your oscilloscope. If a capacitor has opened or has a high emf, you can easily see the high ripple (noise)voltage across the capacitor.Try comparing the good circuit board with the bad as far as voltages or wave shapes and this should show the fault.Try comparing the good circuit board device measurements of the diodes, transistors, etc with the bad board.If you can find a point of difference, I can help you to proceed further.What is the input voltage to this power supply? Why use 36V? Is this the voltage into the power supply from the power transformer post rectifiers?

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: August 18, 2013, 09:07:25 pm
content: connorwk said he didnt have any of the larger capacitors,and there wasn`t that many to swap and try.I`m not doubting your experience,but caps can be bad even with a flat top and not spewing its guts out.Only trying to help

author: connorwk
author_rank: Contributor
timestamp: August 18, 2013, 09:25:53 pm
content: The computer has an external 115v AC to 36v DC power supply then that is fed into the computer and this board turns it into 5v thus it being a 36v to 5v DC-DC converter.I'll start testing all I can with my multimeter now. Sadly I do not have an oscilloscope other then a 1960s one that I think one of the vacuum tubes in it are bad, but thats besides the point.fluxcapacitor:I did swap all the electrolytes from the working board and those two ceramics as you told me to and I even put the ones from the broken unit onto the working one and it still didn't work and the one that did work worked with the caps from the broken one so it is NOT the caps. I know caps commonly fail now adays but most of the older stuff I have worked on say 20 years or older the caps never seem to be the problem.

author: Shock
author_rank: Super Contributor
timestamp: August 19, 2013, 06:16:31 am
content: Wouldn't he need to apply a load to the circuit to test the output voltage outside of the computer?

author: JoeO
author_rank: Frequent Contributor
timestamp: August 19, 2013, 09:10:20 am
content: Quote from: fluxcapacitor on August 18, 2013, 09:07:25 pmWe have nothing to feel sorry for.You have to use what you have on hand.Since he had known good working caps, it is logical to try to swap them out to determine if they are the problem. It should not take him "hours" to do something like that.The problem now has been narrowed down to "a bad connection, shorted diode or transistor or bad IC or even a turn on/turn off part" or " the diodes, zeners, transistors, regulator chips and/or MOSFET".

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: August 20, 2013, 12:20:01 am
content: Is there 1 external 115v AC to 36v DC power supply or 2If theres 2 then.................

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 01:52:22 am
content: No there is one and inside the machine there are two 36v to 5v converters and in the HD and FD box there are two more power boards 36v to 12v and another 36v to 5v. This computer has quite a few power boards all powered by the one huge external 115v AC to 36v DC power brick (the brick is roughly the size of two old xbox arcade supplies, a bit bigger then that in-fact).Also I think I've only made matters worse I ended up making a mistake and blowing up a few more things on the board.So I'm going to order all the transistors and a new lm393p from digikey and replace all those and all the diodes as-well. I'm going to assume it isn't any of the resistors or ceramic caps but unless someone thinks I should replace them too then I may order some of them as-well (all I'd really need are the ceramic caps as I already have a ton of resistors).Hopefully that will get everything working if not I shall be at a loss for words.Oh also this is what the machine looks like working. Well this is the one I have working.As I have said I have two of the main CPU units and it has a bad power board thus me fixing it.The computer has a modular design making it so you can add HDs, FDs, modem units, ect. onto the side of the machine if you wanted.Anyway I'll be making an order up in digikey and getting what I need to basically rebuild the board.

author: Paul Price
author_rank: Super Contributor
timestamp: August 20, 2013, 10:09:30 am
content: It is just too much work and money and time to try to fix this thing by replacing every component on the board..there are easier ways to get your computer working. It's just bad advice and a poor strategy to repairing anything that has this many components this way. Suppose you accidentally create a solder bridge or insert a new component into the wrong place or the right component backwards, then you will end of spending a dozen hours for a short fireworks show at worst or a dead do-nothing supply after all that work.If the total amp output of the power supply is <=5 amps, you could easily just pull out the whole defective board and replace it with a DIY LM2678 switcher power supply that has only 10 components. It could be constructed in an hour or less and take less time than replacing every part on the whole board. If you need more than 5amps, the LM2678 circuit could be duplicated and supply another 5 amps. And yes, I have built these on perfboard and they work just fine.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 20, 2013, 11:00:55 am
content: Perhaps Dave ought to do a video on fault-findingvswitch hunting. Randomly swapping components without determining the cause of the fault is quite likely going generate two sets of faulty components. It would be a far simpler task to trace out the circuit before replacing every component on the board. Tracing out the circuit would, at a minimum, be an education and it might just give you some clue as to how to track down the fault and as to what caused it.

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 02:26:39 pm
content: I'm not really replacing all the parts on the board just the 12~ transistors (about 5 of the transistors are just 2n4401s) and the lm393p chip plus a few diodes.Building a whole other circuit may be easier but then this computer isn't quite original and also there are other pinouts on this boards of which I don't know what they do since I haven't looked into them yet so this board may do a bit more then just 36v to 5v.

author: Paul Price
author_rank: Super Contributor
timestamp: August 20, 2013, 03:40:59 pm
content: Check the connectors for corrosion. You can determine the voltages output by this supply with your DVM at the connector of the the working power supply board.Rather than replace all these transistors just measure their base-emitter, base-collector, collector-emitter junction resistances and look for shorts and open junctions. You can also compare the collector-emitter resistances of the suspect transistors to the working board.It's just a hunch, but I would bet giving you better than even odds that replacing all these transistors would accomplish nothing.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 04:46:16 pm
content: I do believe the original schematic would make fault finding easier, particularly if you get sick of randomly replacing parts and hoping for the best.

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 05:10:43 pm
content: Well if you have and or can find the original schematic then great! But this is from 1984 and these computers are already pretty rare as it is the power boards in the are probably just as rare if not even rarer. I have in a previous post given model numbers and such so if you would like to look for it that would be great but its about 20 bucks for the transistors for two boards so I think I will get them but the only problem is I can find most of the transistors but some of them being from the 80s are unknown parts.If someone would be willing to look at a schematic and tell me whats probably wrong I could I guess draw one up with the known parts and put part numbers in for the unknown parts but that's about all I could do.Also could anyone tell me what these transistors may be.0100 D467TI8423 BThose are two transistors I cant find datasheets for. Also there is another transistor that shows two diodes anodes out and cathodes connected on the center pin having the part number of C10P048. I couldn't find a datasheet on it but I assume this would work in place of it?http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=135187593&uq=635125971238011117

author: Zad
author_rank: Super Contributor
timestamp: August 20, 2013, 05:24:06 pm
content: Quote from: Shock on August 19, 2013, 06:16:31 amThis.Some SMPSUs will fail to start if the main rail doesn't have a load on it.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 20, 2013, 05:24:33 pm
content: Quote from: connorwk on August 20, 2013, 05:10:43 pmTry 2S D 467, and are you sure that is TI8 ? Could it be TIP 42 B ?For the amount of time you've already spent on this you could have traced-out the circuit.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 05:25:30 pm
content: Quote from: connorwk on August 20, 2013, 05:10:43 pmYeah, old stuff can be a pain to repair sometimes.OK, I think I've tracked the schematic down, you'll have to eyeball it and see if it's a match.This looks like the patent for the supply, complete with schematics and mode of operation.http://www.google.com/patents/US4538073Original Scan:http://bitsavers.informatik.uni-stuttgart.de/pdf/convergent/patents/4538073_Modular_power_supply_system_May83.pdfAs for any strange part numbers, post them here and someone might be able to help out with what they are. Most parts will have modern day replacements that are cheaper.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: August 20, 2013, 06:26:13 pm
content: The double diode is likely a pair of schottky diodes for rectification coming out of the transformer. Anything with a reasonable voltage and current spec should be just fine.However, checking these parts in circuit is simple. Just put on your diode check mode and measure across them. You should find a ~.6v drop on the transistors (both legs) and 0.3ish volts for the schottky diodes. If they're not shorted they're likely good.Another thing; if it has no output, the problem is likely in the high voltage side (if the schottkys aren't shorted). It's exposed to the mains and therefore susceptible to spikes, etc. On a simple switchmode like this I'll run through the high side semiconductors with the diode check, which should take less than 5 minutes. Then I'll check the resistors starting with the higher wattage ones because they're more stressed. These check in circuit just fine; all your looking for is something close to their value. They fail open circuit, so anything less than their rating indicates they're good. If the fuse hasn't blown, likely the driver transistors are fine. I wouldn't even begin to bother with the low voltage side except to have a visual look at the capacitors.When you find the problem and fix it, initially power it with a series light bulb to protect the new parts while you make sure it's now functioning normally. Often blown transformer driver transistors are a symptom of some other problem.Replacing parts willie nilly is a waste of time. Find the problem and fix it.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 06:33:00 pm
content: Quote from: Paul Moir on August 20, 2013, 06:26:13 pmIt's actually a problem in a DC to DC converter module (36v input), so no mains in this case.I think this is the circuit diagram of the module, though not confirmed yet.http://patentimages.storage.googleapis.com/pages/US4538073-3.png

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 06:42:06 pm
content: Andy Watson:I am 1000% sure it says.0100TI8423It has clear printing and I have good vision so I am very sure.If you think it is 2S D 467 then I guess that should be the part I use. Since digikey doesn't have that specific part would this do as a replacementhttp://www.fairchildsemi.com/ds/2N/2N6517.pdffor this part?http://pdf.datasheetcatalog.com/datasheet/HitachiSemiconductor/mXwvrqw.pdfZad: I put the supply IN the computer to test it so I am very sure it has a load when I test it. Also I know it supplys power even without a load so it doesn't matter anyway.Crazy Ape: Thanks I will look it over It seems right considering all the computers electronics where made by Convergent and that's who the patent was issued to. Although some things seem off on it so I will have to do a close look over. Thanks very much though hopefully it is it the dates seem right so it may as-well be it.Paul Moir/Crazy Ape: Crazy Ape is right this has nothing to do with mains power just DC to DC also Paul I know replacing parts seems like a bad idea but this is posted in the beginners section for a reason. I am a beginner and don't know where to start testing and the next best thing I could do is just replace parts. Thanks for the advice now that I know this I can start testing parts as you have told me. Only real problem is on this board there are a TON of resistors and a bunch are in parallel so testing in circuit may be a bit of an issue. I will do the best I can.I appreciate all the help with this. Thanks!

author: Andy Watson
author_rank: Super Contributor
timestamp: August 20, 2013, 06:53:22 pm
content: Quote from: connorwk on August 20, 2013, 06:42:06 pmIn that case I would think that the 8423 is a date code.QuoteNow that you know it's an NPN transistor why don't you check it with your meter - as somebody has suggested further up the thread. If you must replace it, have a look on ebay - it appears to be awash with them.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 06:53:59 pm
content: Take note of Paul's hint with the light bulb, only in this case you would use three 12v globes in series, and place them in the 36v input line to the DC/DC converter module.Seriously, if you don't do this and you miss a bad part during your replacement, you have a good chance of seeing you new parts fry.The theory is, that if there's a short in the circuit, the bulb will light full brightness and take the load rather than the circuit.

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 07:09:21 pm
content: Andy Watson: Actually your probably right I just looked at another board and it has this.0100TI8441So I guess this transistor is just a strange cheap made transistor that I most likely won't find out what it is unless that schematic is right and it tells me what it is.I guess I will check the npn with my meter then but what does "Epitaxial" mean does it make it a special npn or is it just some other way its made and it works the same as a regular npn?Crazy Ape: Ok I shall be sure to do that then and hopefully I won't see anything fry.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 07:42:04 pm
content: Burroughs B25 = Convergent Technologies NGEN workstation.

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 07:55:50 pm
content: Yea pretty much.Just has Burroughs stickers and labels on it.EDIT:Nice going Crazy Ape this appears to be the exact schematic for this power board!Also that is why I cant just make a separate board for this because these boards can be used as a 12v source as-well when a select pin is active. So fixing this board would be best.Now to go through the schematic and find out what is what.Thanks again!The only issue with this schematic... Well all the part labels are incorrect between the board and the schematic itself... So now I need to track down and relabel everything. It may not be the final revision either so some things may be different on the patent then on the board too... Hmm...

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 09:09:52 pm
content: Quote from: connorwk on August 20, 2013, 07:55:50 pmI was half expecting the component labels to be a mess, but the actual circuit itself should be very similar, if not the same as the patent.Now you can at least work out if the mystery transistors are PNP or NPN.This might help you remember which is which in the diagram:PNP=Point iNPlease.NPN=NoPoint iN.

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 09:28:03 pm
content: Hmm... The schematic seems a bit more different then I thought... I know I have 5 PNPs on my board and in the schematic I only see two PNPs... Also there are 4 NPNs on the schematic while on the board there can be 4 with the know npns and mystery parts but it just seems odd that there are 3 missing pnp transistors on the schematics... Some of the schematics seem right and its odd... I guess this is a different rev so I may have to make a new schematic using the old one as a starting point.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 10:56:57 pm
content: Who many amps does the board need to supply?There is an easier way.

author: connorwk
author_rank: Contributor
timestamp: August 20, 2013, 11:41:06 pm
content: I am unsure of how many amps the computer needs but there are an absolute ton of dip chips one multiple boards all being powered so probably a good amount. If your suggestion is to make a different board and throw it in there I will have to decline it as I like to keep these old machines as original as I can so I would rather spend 50 dollars for all new parts to put on this board then to make up a 10 dollar board and slap it in there. Just my personal opinion.

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 20, 2013, 11:52:43 pm
content: OK. But what is your plan if one of the transformers is shot?

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 20, 2013, 11:54:33 pm
content: Quote from: connorwk on August 20, 2013, 11:41:06 pmThat's fair enough, I like to keep things original myself.If I had to cheat, I'd grab an adjustable buck converter, replace the adjustment pot with two fixed resistors (set for 12v / 5v) and an electronic switching scheme to switch them based on the voltage select line. So no, not really making a board from scratch, but certainly not original.I just looked at the schematics in the patent, that voltage select is a jumper that's either in place or not in place to choose 5v or 12v for the module. It's a manual setting, not under control of any electronics. You don't need the above mod. You could just set the buck converter to 5v or 12v depending on what the dead board is set to and put it to work.Tech has changed somewhat in the last 30 yearshttp://www.aliexpress.com/item/DC-DC-8-40V-to-3-30V-8A-Switching-Buck-Power-Supply-Module-Step-Down-Converter/720982862.html

author: connorwk
author_rank: Contributor
timestamp: August 21, 2013, 12:05:14 am
content: dfmischler: If a transformer is shot (which I highly doubt it is) I think I'd be crazy enough to take it out and rewind it.Crazy Ape: Yes the tech has changed a lot hasn't it. If I had to do anything I'd probably do something along what you have said. The only strange thing about this supply is that there are two other pins on this supply. A power inhibit line and a 33khz sync line. That sync line is so that it can tell if a supply isn't present in the machine and if it isn't present or has failed then the machine will not power on. Thus the other problem with trying to integrate something else. I think I am really stuck with fixing this supply unless you want to design a full new supply with syncing and all.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 21, 2013, 12:18:18 am
content: Quote from: connorwk on August 21, 2013, 12:05:14 amI edited my above post slightly, since you don't need voltage select, just set the right voltage for the module.You can likely ignore the sync line, they are all tied together (all the modules) and connected to a 33khz sync generator that is external to the DC/DC converter module. I don't see how this can detect a failed supply in any way. You'll find that since the buck converter uses it's own oscillator, the sync line can be ignored.Power inhibit could be used to control a FET placed on the output of the buck converter, having the desired effect.

author: connorwk
author_rank: Contributor
timestamp: August 21, 2013, 12:21:44 am
content: Alright well I'll try to save this one first then go on to brewing up something custom.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 21, 2013, 12:28:17 am
content: Quote from: connorwk on August 21, 2013, 12:21:44 amIt's always good to have a plan-B, even if you don't need to use it.The patent tells us what sync id for:A 33-kHz generator 16 is shown coupled the power bus 19 to route a generator signal the various system DC-to-DC convertors. Generator 16 produces a synchronizing signal to operate all of the DC-to-DC convertors in unison to avoid beat frequencies and other such interference. As a result, the system operates more efficiently while the DC-to-DC convertors do not produce annoying buzzing noises that might also interfere with operation of the equipment and/or annoy a system user. A horizontal sync generator 17 is shown coupled to DC-to-DC convertor 14 which operates monitor 15. The monitor's DC-to-DC convertor is operated at the convenient horizontal sync generator frequency to avoid unnecessary and redundant generating circuitry. Interference is not produced by such arrangement because the monitor is remotely located from the system modules.Well, the buck converter is likely running around 150kHz or there abouts, and being so far away from 33kHz, I'm not sure you'll notice any beat frequency issues.

author: connorwk
author_rank: Contributor
timestamp: August 21, 2013, 01:49:13 am
content: Your right its a good idea to have a backup plan.http://www.ebay.com/itm/Astec-AA7281D-Unisys-5-12V-DC-DC-Adapter-/161081266905?pt=UK_Computing_Servers&hash=item25813112d9This is mine.Just found it on ebay. Now its going to be cheaper for the few parts I'm buying from digikey but if they don't work then I guess I shall get this.Also I sort-of blew up a working one aswell so now I have two dead ones two working ones...Four working if you count the two in the HD/FD unit. But anyway I'm not toying with any other working ones. All the transistors I could find replacements for come to a total of only about 20 dollars I'd guess with shipping so. And that is for both the broken boards so its not that bad if it all works. The only real issue I have as of now is what to do about the one transistor that is a mystery as of this moment. That 0100 TI thing... I will keep working on the schematic but other then that I could only hope it is still functioning and replace all the other transistors.

author: connorwk
author_rank: Contributor
timestamp: August 21, 2013, 02:27:19 am
content: Well scratch me saying I'm missing a bunch of pnps and have extra npns as I mistaken a few npns as pnps so It appears this schematic is more correct then it is wrong. Hopefully this will give me what these no name transistors are.Oh also question.Do you think I can use this transistor.http://www.fairchildsemi.com/ds/2N/2N6517.pdfIn place of this transistor?http://pdf.datasheetcatalog.com/datasheet/HitachiSemiconductor/mXwvrqw.pdfI'd like to order everything from digikey at once instead of having to get a few parts seperately from ebay but digikey doesn't supply the old 2sd467's and what I could find on digikey were these 2n6517's. I wanted to know if they were compatible parts as their voltage ratings were much different. I'd very much appreciate it if someone could look at that datasheets and tell me if the 2n6517's would work in place of the old 2sd467's.EDIT: I found what that strange 0100 part is its the part labeled IC101 on the schematic near the bottom left (if you rotate it clockwise so its readable).http://patentimages.storage.googleapis.com/pages/US4538073-3.pngIt looks like a diode with a line coming out of it between the line and the tip of the triangle. Now being a beginner I do not know what that is or what even to look up to find out what it is. Anyone know what it may be? Its in a standard transistor looking package and that's what it looks like on the schematic so. I have no idea myself.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 21, 2013, 06:02:38 am
content: Quote from: connorwk on August 21, 2013, 01:49:13 amJust be aware that the image is quite possibly just a stock image and not the actual item. Someone else on ebay is using the same image.http://www.ebay.com.au/itm/ASTEC-AA7281D-UNISYS-5-12V-DC-DC-ADAPTER-/360476664474Also, if you do decide to play with the DC/DC modules from the HD/FD unit, be mindful of the 12v jumper being set.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 21, 2013, 06:44:50 am
content: Quote from: connorwk on August 21, 2013, 02:27:19 amThe 2n6517 has some subtle differences when compared to the 2sd467 (2n6517 has higher specifications) but looks like it should work, someone else might like to chime in on this one though and give their thoughts.IC101 is a thyristor of some description, it looks like an SCR symbol but the zenner like lines in the symbol make it something else. I can't say I've ever seen that exact symbol before, sorry.

author: dr_p
author_rank: Frequent Contributor
timestamp: August 21, 2013, 06:56:44 am
content: Quote from: Crazy Ape on August 21, 2013, 06:44:50 amTL431

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 21, 2013, 07:31:14 am
content: Quote from: dr_p on August 21, 2013, 06:56:44 amThanks Dr. PSo it's a 'Programmable Shunt Regulator' (but might not be the same spec as a TL431), that make things interesting since we don't know what it's programmable range is.Connorwk, for this particular component I recommend you get a voltage reading from one of your known good boards, then we can see what voltage it's set to.

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 21, 2013, 10:17:44 am
content: Quote from: connorwk on August 21, 2013, 01:49:13 amI think this should be plan A. Don't wait to buy it, or at least make an offer on it. Ask the seller questions if needed, but it's not like there are 50 of these for sale on ebay.

author: connorwk
author_rank: Contributor
timestamp: August 21, 2013, 05:25:13 pm
content: dfmischler: The reason that is not plan A is it is cheaper to get the parts for two boards and fix both boards while it is more expensive to buy that ONE and then still have a machine with a broken supply. So I shall try to repair both first then if I fail I'll buy one to get back to where I started I guess.Dr.p: Thanks for the help!Crazy Ape:QuoteThose are the worries I had as-well but I was unsure if those voltages worked the same way as say the size of a resistor, were you can have a quarter watt resistor or a one watt resistor that they will work the same as long as its more wattage then the circuit needs and they are the same value. Hopefully someone will chime in and confirm if it'll be an appropriate replacement or not.Quote"The output voltage may be set to any value between VREF (approximately 2.5 volts) and 36 volts with two external resistors."That came out of the datasheet for the TL431. Are you worried the new part may need different resistor values to give the voltage I will need out of it?Oh also this is the chip I will need to get as the fairchild TL431 that datasheet is for seems to not be on digikey.http://www.digikey.com/product-detail/en/TL431AILPR/296-10183-1-ND/404841

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 21, 2013, 06:23:34 pm
content: Quote from: connorwk on August 21, 2013, 05:25:13 pmThe TL431 is a good guess at the part based on the circuit, I just worry about the 0100 marking, is there anything else written anywhere on the device?There are Programmable/Adjustable Shunt Regulators other than the TL431, and some support different voltages, setting resistors etc.

author: connorwk
author_rank: Contributor
timestamp: August 21, 2013, 06:50:22 pm
content: I looked at all 4 boards and these are exactly what I found on all four.0100 0100 0100 0100TI8441 TI8441 TI8423 TI8423The first two came out of the same machine and the last two came out of the same machine so they may still be date codes but they may also just be part numbers and they ended up using a different part. I can open the HD/FD unit and check those two supplies as-well if you'd like not much trouble at all.Also just for your information I'm pretty sure the board that these supplies plug into set the pin for weither it will supply 12v or 5v so I could take the 12v board and put it in a 5v socket because it is set on the board its plugged into not the power board itself.

author: Shock
author_rank: Super Contributor
timestamp: August 22, 2013, 11:31:54 am
content: Quote from: Zad on August 20, 2013, 05:24:06 pmIt's the first thing I thought of.But swap testing if done logically will hopefully prove where the fault is.If there is two boards I would next be taking voltages around the board and current at the load and compare the two.I would have thought this is the next logical step after a physical check.But one of those big resistors had a dry joint on it and I would have touched up the solder joints or if someone had messed with it before me I would be checking that out instead.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 22, 2013, 12:45:10 pm
content: Quote from: Shock on August 22, 2013, 11:31:54 amI agree, however, the keyword is logically. To logically swap components you have to have some knowledge about their function in the circuit. So far we have a vague schematic from a patent, which may or may not be the right one. Without detailed knowledge, randomly swapping components is equally likely to fry both sets - a theory that appears to have been confirmed within this thread:QuoteHang-on a mo.... didn't somebody predict that would happen, about 30 posts ago?QuoteI still think the 8441 and 8423 is the date code. 8423 = 23rd week of 1984, that would tie in with date of these power supplies. The 0100 is likely to be the manufacturer's abbreviated part number. TL431 or similar is probably a fair guess. If you can't find the original manufacturer's data you might have to measure its voltage on a working unit.

author: dr_p
author_rank: Frequent Contributor
timestamp: August 22, 2013, 01:28:22 pm
content: @connorwk : I sudgest you readall of this, or at least read thisparagraph.PM me if you need more info on SMPS functionality and troubleshooting and want more learning material.

author: connorwk
author_rank: Contributor
timestamp: August 22, 2013, 04:00:15 pm
content: Shock: Pretty sure no one else have even taken the metal plate off the back of the circuit board before me. I will go around and freshen up all the solder joints on the board to make sure everything is good by the way to make sure there aren't any dry joints.Andy Watson: Yes you did predict it and a good prediction you've made... But it wasn't from swapping the parts it was from an accident on my behalf... I was soldering on a part from the other board and I soldered on one of the three pins while I bolted it to the heat sink then forgot to solder the other leads in and went to test it instantly hearing a loud pop and a different part on the board blew most likely damaging a bunch of other things as-well. So its indirectly from swapping parts yes but it wouldn't have happened probably if I payed a bit more attention. Now as for measuring voltage on the 0100 part where am I to read the voltage and how shall it help me in determining if the replacement part (http://www.ti.com/lit/ds/symlink/tl431a.pdf) will work? Sorry for the ignorance but I've put the post in beginners for a reason.Dr.P: I'll be sure to try and read most of it especially that paragraph. Thanks.Edit: Dr.P this seems to have to do with regulators that turn wall voltage AC down to DC not DC to DC supplies. As this is talking about HV filtering caps and fuses and all the such as which my board has none of its a simple DC to DC converter.I'm working out the schematic to try and label everything as it is on my board but as it seems that schematic is the EXACT thing I have if anything maybe a resistor or two off. But everything seems the same so you may look at that for reference and tell me where there are HV caps and or fuses but I do not see any on my board or the schematic.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 22, 2013, 04:32:07 pm
content: Quote from: connorwk on August 22, 2013, 04:00:15 pmThis from one of your earlier posts:QuoteBasically, yes.There used to be a whole family of TL43x type regulators - only the 431 seems to be readily available now. There are only three pins on the device, if you measure across each possible combination of pins it should cover all eventualities! What we want to know is what voltage it's regulating at so that you can calculated the resistor values - assuming it isn't a actually a 431 - and assuming that the original is broke.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 22, 2013, 04:56:29 pm
content: Quote from: connorwk on August 22, 2013, 04:00:15 pmThe next useful step would be for you to show us the completed schematic - it might help us give you a more directed response - rather than stabbing in the dark. (Not guaranteeing anything though)

author: dr_p
author_rank: Frequent Contributor
timestamp: August 22, 2013, 05:28:48 pm
content: Quote from: connorwk on August 22, 2013, 04:00:15 pmit's the same in a mains powered SMPS: after the bridge rectifier and large filtering cap, it's still a DC-DC converter

author: connorwk
author_rank: Contributor
timestamp: August 25, 2013, 07:25:09 pm
content: Ok so the schematic for this device would take a lot of work but what I can tell you is the voltage at the programmable shunt regulators reference is 2.5v at the cathode is 20v and the anode goes directly to ground.

author: connorwk
author_rank: Contributor
timestamp: August 29, 2013, 02:26:00 am
content: Well I fixed both of the supplies!For about 20$ for a bunch of the on board parts I ordered from digikey.I just went and replaced every part I had from digikey except the replacing the odd 100 part since I wasn't sure if the part I found would be an exact replacement I just hoped it was still good... And it was! Well thanks for the help everyone!

author: JoeO
author_rank: Frequent Contributor
timestamp: August 29, 2013, 03:58:37 am
content: Congratulations. Nice work!