90's Delta Power Supply Repair - Page 1
Forum section: electronics / repair

author: Max1636
author_rank: Contributor
timestamp: July 17, 2021, 07:13:14 am
content: I have a Delta DPS-300EB Rev. A Power supply for an Apple Network Server 500/132 that's currently not working, I'd really appreciate any help that could be provided by some of the experts on here as I've given up on Facebook groups. As far as I can tell there are no schematics for this unit and even searching the Delta or Apple part numbers give almost no information.So when I first received the power supply it would instantly blow the internal 8A fuse. I replaced the main bridge rectifier as I found it to be faulty, after powering up again the NTC thermistor blew up, so I replaced it and powered the PSU up only have the same thing happen again unsurprisingly (Dave Doh!). I then discovered a triac with all 3 pins shorted which I replaced. The PSU would now no longer blow the fuse and is generating 165v DC X2 at the main caps to make the 330v DC.However all is still not well, like most PC power supplies I believe this PSU should be generating a 5v standby voltage which it's not doing. I'm suspicious that the reason could be due to a small board near the main caps that I think supplies the 5v standby board. (Update: I don’t believe this board is the issue and it doesn’t support the 5v standby board) This board gets its own Active and Neutral supply and has its own rectifying circuit that makes 330v DC also but no voltage seems to get out of the board. With my limited testing tools I've tried to get all the components on the board but I can't find the fault.I'll add photos of the board and again would really appreciate any help with this, TIA.FYI the blue wires on the board were just temporary for testing.

author: trondl
author_rank: Regular Contributor
timestamp: July 17, 2021, 12:14:32 pm
content: I just chime in here to say that I also have an ANS 700/150 with a secondary faulty psu.The first psu is still ok, although I have problems installing AIX 4.1.5 which is unrelated (linux and AIX 4.1.4.1 installs without issue).It’s probably the last surviving unit here in Norway.If you happen to have access to the last AIX patches for 4.1.5 I’ m interrested!

author: Max1636
author_rank: Contributor
timestamp: July 17, 2021, 12:40:50 pm
content: If you ever decide to take your second PSU apart please let me know. I’ve never had my ANS working. Very cool to hear you have a 700.

author: LateLesley
author_rank: Frequent Contributor
timestamp: July 17, 2021, 12:49:15 pm
content: Not a PSU expert by any means - but I have repaired a few in my day. One thing I've learned, is suspect every resistor, I've found these overlooked components can tend to burn up and go high resistance quite easily.Looking at that wee suspect board, where you've marked the voltages, it looks like a resistor chain to drop the voltage, before the active stuff. Where you are jumping from 118V to 0.7V, that's a big jump, and would make me suspicious of two parts. one is that resistor R815, and also that IC801. It looks like R803, R816, and R815 are just dropping the voltage down at each step, So I would check they are at their correct values (or close). They usually use multiple surface mount resistors, to keep them within voltage and power requirements due to their small size. But they can burn up pretty easily. Also, the 0.7V seems like a pretty specific diode drop voltage, which also has me thinking IC801 could have shorted internally.So i'd be measuring those resistors, and pulling IC801 to see what it is, and test it out of circuit, to verify it's ok. Don't just think, if the resistor is open, that you've found the culprit - it could be IC801 died, and burned up the resistor. It may be just a resistor, but try and verify the rest first.

author: Max1636
author_rank: Contributor
timestamp: July 18, 2021, 04:55:16 am
content: Thanks or the help, I had the same thought and tested the voltage with IC801 removed which ends up being about 3.8V. For a minute I thought I was onto something but I replaced IC801 and end up with exactly the same voltage. I’ve attached photos of the original unit on the left and the replacement on the right.R804 reads about 10k in circuit which is correct according to an online calculator.

author: xavier60
author_rank: Super Contributor
timestamp: July 18, 2021, 10:42:22 am
content: Referring to neutral as ground, If the TL431's Cathode is shorted to ground, the Reference pin will look like a forward biased diode to ground.I think the circuit's function as a Under Voltage Lock Out.

author: Max1636
author_rank: Contributor
timestamp: July 18, 2021, 10:50:40 am
content: Thanks for the help, I will test this tomorrow. Are you saying the whole board might be a low voltage lockout or just the TL431 part?

author: xavier60
author_rank: Super Contributor
timestamp: July 18, 2021, 11:14:04 am
content: Quote from: Max1636 on July 18, 2021, 10:50:40 amI'd say the whole board either allows the control circuit to operate or supplies start power somehow. I can see the rectifier diode charging the larger capacitor but not what it's suppling power to.

author: Max1636
author_rank: Contributor
timestamp: July 18, 2021, 11:19:39 am
content: Please let me know if there’s any other photos I can add that help. You can see that extra board top left in the photo. Thanks for your help so far.

author: xavier60
author_rank: Super Contributor
timestamp: July 18, 2021, 12:01:14 pm
content: It's an auto mains voltage selector. When It thinks that the mains voltage is low, it turns on the triac which converts the bridge and split reservoir caps into a voltage doubler.I have seen these auto voltage selectors get it wrong and blow up the PSU. Best is to disable it by removing the triac.When repairing SMPS, I never directly apply mains on the first test because if problems have been missed, a lot of extra damage can be caused. It should at least be powered through a series light bulb.

author: xavier60
author_rank: Super Contributor
timestamp: July 18, 2021, 12:16:20 pm
content: I see there are 2 triacs. Remove the upper one that has the black line to its Gate. The other is for anti-surge.What are the row of 10 pins in the middle of the last photo for?

author: Max1636
author_rank: Contributor
timestamp: July 18, 2021, 12:31:23 pm
content: Thanks allot for the information, this is the most help I’ve got since I first started my attempted repair. So I will remove the triac at the top left, is this only so that the circuit doesn’t get the voltage wrong and damage something?Did you notice on the small board that one of the pins that I marked ‘G’ connects to that triac? Fairly sure to it’s gate pin. Could you explain why that is?I have heard about using a light bulb but I didn’t completely understand how to do that? As I said the power supply seems to be somewhat working now as I have 165v at each main cap connected in series to make 330v DC.The 10 pins connect to another kind of control board, I will get a good photo tomorrow. I will attach a photo that might help a bit though.

author: xavier60
author_rank: Super Contributor
timestamp: July 18, 2021, 01:05:15 pm
content: Quote from: Max1636 on July 18, 2021, 12:31:23 pmA rail from the control supply comes in on an end pin to R805. Current can flow out of the other end pin to the triac's Gate. There are 2 transistors that are able to shunt this current to ground. One is controlled by the TL431 and the other starts of as always normally on, then can be turn off by a another voltage sensing circuit, a transistor and Zener diode sensing the mains derived voltage on the smaller capacitor.This explains the rest,https://electronics.stackexchange.com/questions/479800/why-do-some-smps-power-supplies-require-an-input-voltage-select-switchI suspect that the control supply has been damaged.

author: Max1636
author_rank: Contributor
timestamp: July 18, 2021, 01:19:40 pm
content: Great thanks this gives me something to work with. This whole time I thought that small board should of been generating voltage because it had an A and N but those pins are only for sensing the voltage then right?I believe the control voltage is generated by the board over to the right, I attached a photo which shows a line that connects the two. That board also has a 330v DC pin which I marked. I will look more closely at the board tomorrow, thanks again!

author: xavier60
author_rank: Super Contributor
timestamp: July 19, 2021, 02:47:12 am
content: R50 appears to be 1Ω from here, not that it matters, it appears to be acting as a fuse on the HVDC.Hopefully only the TOP200Y has broken down and the main SMPS is undamaged. Assuming that the auto voltage selector is the original problem cause.

author: Max1636
author_rank: Contributor
timestamp: July 19, 2021, 02:53:04 am
content: Sorry for the confusion I deleted a previous message because that small yellow capacitor actually isn’t blown. The black soot actually came from the 2 main MOV’s that had previously blown but I’ve now replaced.Still confused with that resistor though because even though I’m not reading anything between the 2 legs it seems to be passing voltage just fine.Would it help if I told you what voltages I have on the TOP200YAI?

author: xavier60
author_rank: Super Contributor
timestamp: July 19, 2021, 02:54:40 am
content: Yes, I'll be back,

author: Max1636
author_rank: Contributor
timestamp: July 19, 2021, 03:02:17 am
content: So on the right pin (Pin 3 I assume) I have 300v DC, although it’s strange it seems to sometimes be 330v DC but maybe it’s just not a great connection with my leads.If I then put my positive lead on the 330v pin on the board then put my negative lead on pin 1 and 2 I get 330v DC. But from the looks of it that middle pin is connected to ground anyway so that makes sense there.Hmm.. So with power off and measuring between pin 1 and 2 I have about 4.8Ohm. That doesn’t seem right does it?Update: Out of circuit I’m still getting 4.8Ohm between the control and source pins. (The left and middle pin).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 19, 2021, 04:23:41 am
content: Aha, a smoking, erm, smoked gun!Is that R50 with a fuckin' hole blown out its side?Ceramics are very uncommon to fail; can happen, but not primary suspects. (On leads anyway. Can be more suspicious for SMT chips, can crack due to board flex/vibration. But still not the first thing.) The one there just looks like its paint has peeled off. But if it's actually dead yeah that's definitely something.Missing aux, that TOP200 is your prime suspect. Small, tall transformer, off to the side, with whatever reg/controller is on it.Mid 90s I'm surprised they splurged for a regulator like that at all (wait, how old is the TOPSwitch family anyway? I didn't know they were around back then.. Aha, introduced '94, cutting edge technology it was!), mostly they used a single BJT blocking oscillator with zener regulation. Such circuits are most common in AT/X PSUs, and VCRs and other consumer video equipment for some reason (and also, semifamously, Apple ]['s).Troubleshooting, in general: maybe you realize this now, maybe it bears noting, maybe others will find it useful --1. 9/10 times, replacing the fuse just begets another blown fuse. Don't be a fool. Something caused that fuse to blow! Ohm it out.The remaining 1/10 times, maybe it died on its own (thermal cycling/fatigue, just a shoddy part, or failed due to mains surge, who knows?), and replacing the fuse is actually all that's needed. Very suspicious, and a bit spooky to be honest.2. Switching supplies all have very typical designs; you have to learn a bit, but once you get the idea you can follow along just reading the board. In this case, to wit (referring tohttps://www.eevblog.com/forum/repair/90s-delta-power-supply-repair/?action=dlattach;attach=1237205;image):Mains input: top right. I see a ground lug with ferrite bead, smaller (5x20mm?) fuse, a couple chokes and caps. Looks to be two common mode chokes (two windings, same direction), and one differential mode (with a yellow/white core I'm guessing?). Two boxy caps are X1 (across-the-line) film type, and the blue discs (sometimes other colors) are Y1 (line-to-ground) ceramic.Top left: rectifier, main filter, and some startup stuff I guess. I haven't traced the circuit on the little riser board but I'm guessing it's related to either aux startup / bias, or precharge/NTC bypass timing circuit. The main FWB would be on that heatsink (on the inside I guess, can see just an edge of it here?), but there's also a TO-220. I don't see a resistor or NTC so I'm guessing there's one just out of view, and what happens is, some moment after power-on (either by a fixed time, or by the main DC supply voltage coming up to near nominal), the TRIAC is turned on, bypassing the resistor and supplying full mains to the circuit.So, we have our first potential points of failure. If the DC bus doesn't come up, the TRIAC turns on into a hard short, of at least momentary nature due to the capacitors (which it might grunt at but still be able to handle?), but if it's fully shorted out then the whole thing is just toast, and the mains fuse must blow to clear it. Note that this won't happen if the startup circuit monitors DC bus; it'll never pull in. In that case, the resistor burns out, because it's dropping full mains power for, like, whole seconds or minutes even, however long it takes to melt, when it was only designed to endure that for a hundred milliseconds!SCRs and TRIACs are pretty robust devices, enough that they can often survive blowing a fuse, though it usually has to be a special very-fast-blow type ("semiconductor" fuse, so named because of what it can protect -- not what it's made of, if you were wondering). Rectifiers (the FWB) are usually a bit more robust in turn, though not so much to avoid the same requirement. That said, I have seen plenty of rectifiers which survived, not only blowing a cartridge fuse, but awhole fucking panel breaker-- these do not open quickly, and a residential circuit probably supplies one or two thousand amperes for a cycle or two, before opening. (The breaker has a magnetic loop that opens it much quicker under sudden fault like this, in contrast to the slow thermal (bimetallic strip) mechanism that opens in seconds to minutes.)Another option for the TRIAC, is automatic mains voltage selection. I don't see a connector on here for a "120/240" switch; it may be just out of view, or jumpered over, but this is another application where a TRIAC can be used. (Which might explain the lack of startup resistor/NTC and so it doesn't actually have inrush limiting.) The function is most likely something like: when total supply voltage is low (under say 200-250V), and after some delay (to allow for initial startup time), turn on the TRIAC, which is connected between neutral and capacitor midpoint. This turns the FWB into a FW doubler, and now you get the full ~340VDC from a 120V input.[Double checking with the underside view, that's exactly what it is, auto voltage setting.][Looking at the output side now, but noticing things about the primary side traces. There are both! That must be an NTC under the FWB heatsink, and it's bypassed by another TRIAC on the inverter heatsink; and powered by an aux winding on the power transformer itself -- so it's only turned on in normal operation. Crazy!][And, it looks like the fly leads off the transformer, aren't a thermistor at all. They look to just dead end, actually... weird. Ah, but I haven't gotten to thermistors yet...]In any case, the big electrolytics get charged, and on to the inverter. The upper-middle heatsink ought to have 2 or 4 transistors on it, probably BJT for this age. Looks like there's some kind of controller board to the right, or control circuitry on board. TL494, SG3524 and KA7500 (and a couple older ones I don't remember) were typical at the time, making this a voltage-mode full-wave forward converter.Further to the right, there's orange wires for a thermistor on the heatsink, and I think a few others -- looks like there's one in the transformer itself, nice, and one on the bottom left heatsink too. These are probably read by a jellybean comparator (or op-amp being used as same -- LM339 and 324 are common sights), along with other status signals like aux voltage or DC bus, to implement UVLO, OVLO (under/over voltage lockout), overtemp, overcurrent, etc. Simply disabling the main controller as a consequence (either with a delayed auto-retry ("hiccup") or latching behavior).On the far right, there looks to be three optos (6 pin DIPs). One should be feedback for regulation, the other two may be for startup trigger or secondary side fault trigger (which would be where the secondary side thermistor tells the primary side to shut down).Going back a bit to the left, the small green toroid with fine wire on it, is likely a current sense transformer. I don't think anyone used current mode controls at this time (for shame), so this is probably just for overcurrent detect. It may also have windings on it for drive power -- when using BJTs in inverters, it's handy to loop back some of the load current into the base drive circuits, so they hold themselves on; it's a latching circuit, and you actually drive it by turning off the transistors (shorting mode commutation, at the drive transformer).Usually, such a transformer looks similar to the aux supply's tall, thin transformer; unless it's just out of view, it may well be a MOSFET based circuit. Although I'm still not sure how they'd get high side drive in there. Maybe a much smaller [gate drive] transformer. Or it could be low-side drive, but that only works with push-pull, which requires very high voltages (double the DC bus, so, 800V+ devices would be mandatory!).I don't think they had bootstrap gate drivers at the time? Not sure when they were introduced. That would be the modern solution though, just a drive IC and a pair of MOSFETs, easy peasy. Oh, or, heh, I suppose there's an outside chance they made their own, a discrete bootstrap driver. That'd be interesting.[Okay, having looked at the layout a bit more, it's not full-wave anything at all(!) -- it actually looks to be one-switch forward converter, and I think there's an aux winding on there, but I don't think it's a freewheeling winding, or not just; this thing may very well be what's called an active-clamp forward converter. I had thought those were a somewhat newer idea! So then, I think there's a TO-247 or TO-3P main switch in the middle of the heatsink, and a TO-220 active-clamp switch nearer the transformer. Also, this explains the, 0.022uF? film cap right there.]Anyway, onward down a bit, the output transformer obviously. And on the left, the aux supply board -- this will be a very typical (application circuit) flyback supply, with an air-gapped ferrite transformer, and it appears they used sinterglass (round blob) diodes with it. Not sure what the other heatsink is, maybe a 7805? The aux supply might be just +12V (or anything 8-20V would likely work for the main controllers) and regulated down for the motherboard's +5V standby (or whatever it uses). Hm, at least, I would assume aux powers the main controller; I don't actually see a path for it. It looks more like the TRIAC is triggered by it..! Well, I don't see the diode, but I'm pretty sure there's one tucked away in there, maybe beside the TOP200 itself, and powering it as well as the main controls.Continuing down from the main transformer: on the right we have a heatsink with rectifiers, probably for the nearby (yellow/white) choke, maybe on the order of say +12V at 10 or 20A?Note that there are multiple outputs, so we expect multiple rectifiers and chokes, and many windings on the transformer.Which, with only the one control, they can't all be regulated, independently; normally a weighted combination is taken, and that works good for uniform loads, but a heavier load on one channel will drag it down, while pushing the others up (cross regulation, "sausage effect"). There are solutions for this (e.g. mag amp used in ATX supply +3.3V) but I don't think they used any here, and probably they're just doing 5V and 12V or something like that and it's fine.Anyway, there's a small heatsink in the middle, maybe a smaller supply, maybe negative, not sure. Heatsink on the right is likely +5V output, maybe another +12 (for the second yellow/white choke)BTW, yellow/white is the color code for Micrometals mix #26, a very lossy powdered iron, mu_r = 75. It's cheap, and that's it. It almost makes better resistors than inductors... but, just as electrolytic capacitors are rather lossy, if we use enough of 'em we kinda don't care. The consequence here is, the inductance is relatively large, to keep ripple current low, and thus core losses.The large inductance puts the filter roll-off at a few kHz. Which means the control can only respond to load changes in some ~ms, and so relatively large capacitors are needed to keep the output impedance low. Electrolytics of the day, also had somewhat more ESR than today, which is both a curse and a blessing -- it amounts to AC losses and lack of filtering (which is improved in turn by the little rod chokes, I think you'll find those are in series with the respective outputs, with caps to ground on either side), but the ESR puts a zero in the feedback loop (i.e., the sense voltage changes immediately, in proportion to a change in inverter or load current), which helps with stability. Which is why, when the caps inevitably dry out (ESR rises, C falls), loop compensation can go south, and maybe just ripple increases, maybe it starts whining or hissing (oscillation). And why, when replacing them, they should be replaced with comparable types -- using too low ESR is also likely to cause oscillation!Anyway, on the far left there's a bigger choke with multiple windings, and I'm willing to bet there's an aux winding on there, rectified (and probably regulated, on the small heatsink to the left?) for whatever -5 / -12V the thing needs (usually not much?). Not sure why red and gold, guessing they're just wired in parallel. And that'll be for like, 5V 40A or something.Oh, also with two fans and a few transistors around, the thermistor down there might be for controlling one or both, or for overall fault as mentioned earlier. Could be both, staged (fan first, then fault).One thing I have no idea about: the stranded (coarse litz?) chokes by the transformer. Maybe, like, dI/dt snubbing or something? Haven't seen that in anything else though. Shouldn't be any power transistors nearby, nor any need for additional conversion or something. Oh, or I wonder if they might be mag amp cores, for reverse recovery snubbing? The 12V supplies might be using high speed rectifiers, they didn't have much schottky in higher voltages back then I think. The 5V rectifiers (under the bigger heatsink) ought to be TO-3P or TO-247 schottky though.Also, as an overall half-wave forward converter type, dual rectifiers are still likely in use -- one from GND to the choke (catch diode), one from secondary to choke (rectifier).Tim

author: Max1636
author_rank: Contributor
timestamp: July 19, 2021, 04:55:23 am
content: Wow thanks Tim, vey helpful explaining the operation of the supply. I’ll be sure to give that a read a few more times to help me understand. Regarding the repair, any idea where I could source a new TOP200YAI? Or a modern equivalent? Do you think it’s strange that it’s reading 4.8 Ohm between pin 1 and 2?Any idea what kind of wattage that R50 resistor would be rated for? Regarding the resistance in circuit I seem to get 1.3M Ohms which seems wrong… As mentioned by others I believe it should be 1 Ohm correct?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 19, 2021, 07:30:16 am
content: Looks like TOP222 is still available. Higher power tho.Pin 1 should be primary side control power, give or take if they put any filtering around it. It may show resistance, but 4.8 ohms does suggest something is shorting it.Tim

author: xavier60
author_rank: Super Contributor
timestamp: July 19, 2021, 08:16:39 am
content: The blown MOVs adds to the likelihood that the auto voltage select was the initial cause of the PSU failure.One mystery is the track under the main board that has been stressed by over current. The amount of damage to the 1Ω resistor doesn't match.Although it looks like a common 0.5W metal film resistor and it actually might be, it should be something that's specified to safely function as a fuse, not possibly cause a fire.Using the data sheet for the TOP200Y, look for possibly damaged components associated with the control pin.

author: Max1636
author_rank: Contributor
timestamp: July 19, 2021, 01:49:58 pm
content: I did notice that track… Do you mean where you can see the exposed copper? I’ve ordered some TOP222YN chips from eBay of all places as they have local stock, could someone confirm that it’s a suitable replacement?Also regarding the resistor would it be unsafe to use a 1 Watt, 1 Ohm resistor from Jaycar? If not I will try to find out what the wattage value is.

author: xavier60
author_rank: Super Contributor
timestamp: July 19, 2021, 04:28:00 pm
content: Quote from: Max1636 on July 19, 2021, 01:49:58 pmYes, where the exposed copper is showing.You could use the resistor from Jaycar but its reaction to an over current event is not known. Ok for a test.These would be a safer choice although I cant be fully certain,https://au.element14.com/vishay/nfr25h0001008ja500/res-1r-5-500mw-axial-metal-film/dp/9474048?st=nfr25hWith parts purchased on ebay, expect trouble. First have a close look for signs that the device markings have been altered.I have had PI parts where a propotion just don't work and the rest work fine.The TOP222YN appears to be a drop in replacement for the TOP200YN.

author: Max1636
author_rank: Contributor
timestamp: July 24, 2021, 03:19:33 am
content: Progress! So all I’ve done is replaced the TOP222YN which has got us closer. However it did fry that small 0.5w resistor at R50 so clearly something is shorted elsewhere. Even after this though I still read 5v at the TOP222YN.Curiously also with my meter on DC volts I have 155v at the small board to the left that some here have thought is an automatic voltage selector, I also have 155v to the gate pin of the triac that it controls which I removed upon recommendation, does this mean that triac being in place could of destroyed the PSU again?

author: xavier60
author_rank: Super Contributor
timestamp: July 24, 2021, 06:28:57 am
content: Just confirming that the TRIAC has been left out of the auto voltage selector?Any sign of the TOP222YN being damaged? Between the Drain and Source pins should test like a diode.

author: Max1636
author_rank: Contributor
timestamp: July 24, 2021, 06:44:11 am
content: Yes I removed that triac like you said. I have 155v where the gate terminal would be so that board is trying to turn on the triac I assume. Why would that be? I don’t believe there’s any damage to the TOP222YN as far as I can tell, I have plenty of spares though as I bought 10. I will test it more a bit later. Thanks very much for your help so far I think it’s very close to getting this working.

author: xavier60
author_rank: Super Contributor
timestamp: July 24, 2021, 07:30:35 am
content: Quote from: Max1636 on July 24, 2021, 06:44:11 amThat 155V likely means nothing, it's about the expected reading between HVDC ground and Neutral.One possible next action is to apply mains while the TOP222YN is removed with a new R50 fitted.Another option is to power the Standby PSU board with low voltage, 30V, with all parts fitted.

author: xavier60
author_rank: Super Contributor
timestamp: July 24, 2021, 07:41:04 am
content: Also check all diodes on the Standby PSU board.

author: Max1636
author_rank: Contributor
timestamp: July 24, 2021, 12:48:37 pm
content: Did some more checking and I’m confident TOP222YN is fine, reads like a diode between drain and source. Couldn’t find any bad diodes on the board. I’m getting 5v DC on the control pin and 16v on the drain pin.. but that was before I removed R50, now I have almost nothing. So somehow R50 was still passing something? Even though I can’t get a reading on my meter… Will have to replace R50 and see what happens as it might of already been bad before.Do you still think using a 1W resistor from Jaycar would be a bad idea instead of a 0.5W one?

author: xavier60
author_rank: Super Contributor
timestamp: July 24, 2021, 01:05:00 pm
content: Quote from: Max1636 on July 24, 2021, 12:48:37 pmYou can try the 1W resistor to see what happens. Do you have a variac so that the mains can be increased gradually?

author: Max1636
author_rank: Contributor
timestamp: July 24, 2021, 01:09:13 pm
content: I don’t have a variac unfortunately no, I’ll try a 1W resistor tomorrow and let you know what happens, thanks again for he help.

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 02:31:32 am
content: So I’ve added the 1W resistor (In a temporary way because I thought it might blow) and now on both sides of the resistor I have about 330v DC. At the pin I highlighted in the photo I’m actually getting 470v for some reason, does that seem normal? I’m also getting 5.76v from the TOP222YN.At the top of the transformer which I imagine is the primary side I have the following readings:1: 330v2: 330v3: GND4: 0vI don’t seem to have anything from the secondary side.

author: xavier60
author_rank: Super Contributor
timestamp: July 25, 2021, 02:51:53 am
content: Quote from: Max1636 on July 25, 2021, 02:31:32 amIf that point is one end of the spike snubber capacitor, then the 470V could be normal. There should be a bleeder resistor across the capacitor, make sure it's ok.The specs for the TOP222YN says that it self current limits at 0.5A and that's for a brief peak at each switching cycle while at full load, nowhere enough to blow a 1Ω 0.5W resistor. It's a mystery to me.The presence of the 470v and the 5.76v on the control pin means that the IC is chopping.

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 03:03:04 am
content: I’ve highlighted the pin that reads 470v from the other side, doesn’t appear to be a capacitor very close by? Thanks very much for the quick responses.

author: xavier60
author_rank: Super Contributor
timestamp: July 25, 2021, 03:12:30 am
content: There are 2 brown disc ceramic caps, one is across the HVDC and the other looks to be the snubber.There should be secondary voltage between the 2 pins that supply the the auto voltage board and the 3rd pin along with respect to HVDC ground.And also possibly 12V and regulated 5V on the isolated end.More: How many times have you replaced R50?

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 03:35:45 am
content: I just realised I have 4.95v coming out of the standby board! That must of only happened after replacing R50 (Which I’ve only replaced once.) I must not of realised before… I’ll do some more testing and let you know what happens, the PSU might be close to working now.

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 08:03:40 am
content: No luck with the server powering on unfortunately. But as I said the standby board is now generating 10v DC which seems odd as I’d expect 12v and 4.95v which is possibly a little low as well.I think it would be best if I can turn on the PSU without being connected to the rest of the system as it has many micro switches need to be in place and could be faulty. There is a pin on the board labelled ON/OFF, any idea what to do with that pin?

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 08:11:47 am
content: So here’s something else. I have 4.95v on the OTP pin on the power supply which you can see in the previous photo. I assume this is over temperature protection?

author: timenutgoblin
author_rank: Regular Contributor
timestamp: July 25, 2021, 08:35:44 am
content: Quote from: Max1636 on July 25, 2021, 08:03:40 amLooking at the photo, those optocouplers might have something to do with OTP and ON/OFF. Maybe ON/OFF is an input and OTP is an output. Try reverse engineering the circuit to figure it out.

author: xavier60
author_rank: Super Contributor
timestamp: July 25, 2021, 08:48:32 am
content: Normally high may be correct for the OTP.Not being fully certain of what voltages are supposed to be outputted by the standby PSU makes things tricky.Measure all of the voltages for now. There might be something damaged near the TOP222YN's Control pin.There appears to be a transistor there which is odd.

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 09:35:38 am
content: These are all the voltages I’m getting at the moment.

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 09:45:22 am
content: I can see that one of the optos does OTP, at one point I had continuity and it would change when powering the PSU on and off but now nothing… Not sure what the other 2 do but one of them has continuity. Still 4.95v on the OTP pin.

author: xavier60
author_rank: Super Contributor
timestamp: July 25, 2021, 09:57:52 am
content: Quote from: Max1636 on July 25, 2021, 09:45:22 amYou will have to research to find the normal state of the OTP.Did you measure the 160V with respect to Neutral or HVDC ground? If it really is 160V it should be restored back to its normally loaded state by placing a jumper wire between the 2 outer holes of the removed TRIAC although I dont think it matters.Does the on/off wire have 5V on it like an ATX PSU?The 13V seems correct for the live side control circuitry.There is a 25V electrolytic across the auto select PCB's power supply.

author: Max1636
author_rank: Contributor
timestamp: July 25, 2021, 10:08:47 am
content: I’ll see what I can do but as far as I can tell there’s no documentation on the PSU as I have searched. I got that 160v with my negative probe on the HVDC Negative. If I use the Neutral pin with my meter on DC I get 6.7v.

author: xavier60
author_rank: Super Contributor
timestamp: July 25, 2021, 10:15:49 am
content: Quote from: Max1636 on July 25, 2021, 10:08:47 amThe 6.7V is the correct reading and seems low so maybe the 13V is low also. What value is the large resistor on the auto select PCB?There should be a Zener connected to TOP222YN Control pin. Is it leaky?

author: Max1636
author_rank: Contributor
timestamp: July 31, 2021, 06:13:14 am
content: Check this out! After giving up trying to get information from someone else with this PSU I bit the bullet and connected the 5v Standby pin to the ON/OFF pin and it powered up! The only issue is the 12v rail seems to be very weak which might be why it wasn’t powering up the server it was connected to. I can’t even power up a standard 3.5” hard drive with it, it also only reads about 10.5-11v. I’d say the PSU likely needs a recap?

author: Max1636
author_rank: Contributor
timestamp: July 31, 2021, 06:25:56 am
content: Fairly sure the issue is just caps now as the voltage fluctuates with change in temperature, voltage goes down when applying heat and voltage goes up with freeze spray.

author: xavier60
author_rank: Super Contributor
timestamp: July 31, 2021, 06:30:51 am
content: I avoid replacing capacitors unless they are known to be faulty.I don't understand the output topology. The photo in Reply #11 shows a yellow choke with 2 windings on it.The next 2 yellow chokes to the right have single windings. The 2 small chokes could be saturable inductors to allow independent regulation of rails. See if you can figure out which yellow chokes are involved with which rails.Also try loading the 5v rail to see how it affects the 12V rail.Can you check for ripple across the capacitors?

author: Max1636
author_rank: Contributor
timestamp: July 31, 2021, 07:40:15 am
content: Hopefully my scribble is of some help. So it looks like the 12v comes from a different spot than the 3.3/5v rails. There are 2 3-pin chips on heatsinks that I’m yet to identify. Worth noting as well probably that the 3.3v rail is high, it’s more like 3.7v. What do I need to measure capacitor ripple? I will load the 5v rail up with something when I can.Also I removed and tested the 2 larger caps on the 12v and they both actually test good.

author: xavier60
author_rank: Super Contributor
timestamp: July 31, 2021, 08:25:28 am
content: Regulation priority is given to the 5V rail. The 2 saturable inductors allow limited independent regulation of the 3.3V and 12V rails.All rails are likely to need some minimum load for proper regulation.A DSO is needed to check for ripple and other stuff as need arises.It would also be handy to know if the main board is attempting to enable the PSU.

author: Max1636
author_rank: Contributor
timestamp: July 31, 2021, 12:08:12 pm
content: Well I think I just proved your right about the 5v rail getting priority… maybe. When I connect this 12v 6A fan to either the 3.3 or 12v rail the supply can’t handle it. But the 5v rail has no issue, also the 12v rail actually jumps up to 12v instead of 11v with the load connected.I will see if I can check if the server is powering up the PSU when I can but it looks like both the 3.3 and 12v rail are weak, could this just be because they aren’t being loaded properly? I still feel like something isn’t right. Thanks again for getting me this far.

author: Max1636
author_rank: Contributor
timestamp: July 31, 2021, 01:42:21 pm
content: Just connected the PSU to the system and it powered right up! Looks like it’s all sorted! Thanks so much!

author: trondl
author_rank: Regular Contributor
timestamp: August 01, 2021, 04:02:30 pm
content: Congratulations!What would you say was the offending part(s)?IIRC, many had issues with a dead psu already in the early 2000s, so it may be a common failure.I might attempt to repair mine now.If you need some help on this quirky machine, I may know a trick or two.Hope you have replaced the clock battery.

author: Max1636
author_rank: Contributor
timestamp: August 02, 2021, 12:20:58 am
content: Hard to say exactly what the cause of the failure was it was as I probably blew up a few things in the process… But as suggested earlier on possibly the reason was the automatic voltage selector, possibly thinking it had 120v and was doubling the voltage but was actually running on 240v. I’m not completely sure though. I’ve removed the triac that the automatic voltage selector controls anyway so it shouldn’t be able to damage anything now.You wouldn’t happen to have an .iso of the original AIX install discs would you? The old clock battery is long gone so no corrosion there luckily.

author: trondl
author_rank: Regular Contributor
timestamp: August 11, 2021, 02:57:20 pm
content: Max1636: PM was sent some days ago