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Repair/replace IBM 5110 power supply board (or seeking anyone experienced in similar work)

voidstar78

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I'm looking for some help to repair/replace an IBM 5110 power supply.

I have a 3rd fully working 5110 intact and with working power supply, so I have a functioning reference on how they are supposed to be wired.

But I also have two 5110's that I think are having power supply issues. I see where the main power lines comes in, via 120Vac wall adapter, and confirmed that power is reaching the board. From there, the job of this PSU is to provide an assortment of voltages: -12V, -5V, 5V, 8.5V, 12V, on some output headers on the far right side edge of the board.

At some point I was getting these voltages in the A1/Y1 PSU adapter. But long story short, now I am not.

If anyone has an otherwise for-parts, trashed, or non-functional 5110, or perhaps a power supply pulled from such a system - let me know.

Or if anyone has expertise in identifying replacement comments to repair these PSUs, or knows a trusted contact that may - please let me know.


I think basically I need to fix this:

IMG_1520B.jpg


To look like this: (the yellow wires on the right are output connections that go to the external ports and also straight to the IBM PC 5110 A1 mainboard in a 24-pin header called Y1, of which only 23-pins are used).

IMG_1519A.jpg




Below is a highlight (red rectangle) of the missing components that need to be replaced. I actually do have these components (non-working, they were damaged when cut out), but getting part numbers to determine suitable replacement will still be difficult. The red arrow below is where the 120V input goes into. If anyone knows what the "brown" components on the left side (see above, they are missing in the "other" PSU pictured below) - they are not capacitors, they actually feel like possibly ceramic and are hollow in the center (like a thick straw). Then there are some resistors and "black components" missing near the center.

I'm not able to do this kind of soldering myself. I can ship just the PSU boards, which should be straightforward to bench test (apply 120V on the left, get DC voltages out on the right).

IMG_1520B_small_missing.jpg



Thank You!
 
I have a thread on the 5110 PSU: https://forum.vcfed.org/index.php?threads/ibm-5110-power-supply-schematics.73100/

You have removed four power resistors and those were damaged when removing them, right? You could measure the resistance of those in the PSU that is working. The size give an idea about what power rating is needed. Why was those power resistors removed in the first place. It is quite unlikely that power resistors go bad in a PSU.

Are you absolutely sure that no other components are damaged in the faulty PSU. Mine hade one broken power switch transistor.

But after replacing that one it still didn’t work. I checked about every semiconductor. All checked fine. Since there are no schematic I thought about reverse engineering it but it fell on the fact that there are no documentation on those IBM aluminium cans in there.
 
This was their condition when I received them. The PSU with the missing components had those components in a small plastic bag (just the larger components, I don't see the smaller resistors -- and no information on why they were removed).

I'm trying to avoid opening the working PSU, only as a last resort.

Couple other options:

(a) we know where the 120V comes in, and what DC voltages come out (and which pins on the left side). Maybe an entirely new PSU could be built. The PSU fan (and the internal tape deck fan) are powered independently from this board, this board just feeds the external connectors at the back, and the A1 mainboard itself. [ I'm not yet really sure about the display, on where it's powered from - I mean I see a bunch of plugs it has, but didn't follow if they go come from the power box directly below the display or routed from the PSU ]


(b) the Y1 power connector pins on the A1 board, they go all the way through the board. That pinout is well documented, maybe we could feed the -12V, 12V, 8.5V, -5V, +5V from a kind of external power supply that uses the backside of the pins (if at least just temporarily, to see if the system otherwise works at all)
EDIT: attached photo of the Y1 pins "all the way through" the board - so you can get to them from either side. Then the corresponding pinout from the IBM MIM manual (there is more elaboration about the DC outs on the next 2 pages after this).



Aside from the fuse below the display, are you aware of any other fuses in this system? I thought at some point I had read about a 2nd fuse, but I'm not seeing any (just the one twist-open fuse at the bottom below the RUN switch).
 

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Also, any idea what the gray plastic knob at the bottom center in my images is for? I assume to calibrate some frequency (on the IBM 5150 there is a somewhat-similar knob near the CPU used to calibrate the CGA).
 
And I know the following attachment isn't a hardware schematic, but it was in an extra set of foldouts that came with the set of books I have for the 5110. Maybe it offers some insight.

At least, it confirms to me the display is powered via the Y1 connector.
 

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Also, any idea what the gray plastic knob at the bottom center in my images is for? I assume to calibrate some frequency (on the IBM 5150 there is a somewhat-similar knob near the CPU used to calibrate the CGA).
I guess it is setting the output voltage. It is close to the two optocouplers that are in the feedback path so I think there are some circuitry that control the outputs.
 
This was their condition when I received them. The PSU with the missing components had those components in a small plastic bag (just the larger components, I don't see the smaller resistors -- and no information on why they were removed).

I'm trying to avoid opening the working PSU, only as a last resort.

Couple other options:

(a) we know where the 120V comes in, and what DC voltages come out (and which pins on the left side). Maybe an entirely new PSU could be built. The PSU fan (and the internal tape deck fan) are powered independently from this board, this board just feeds the external connectors at the back, and the A1 mainboard itself. [ I'm not yet really sure about the display, on where it's powered from - I mean I see a bunch of plugs it has, but didn't follow if they go come from the power box directly below the display or routed from the PSU ]


(b) the Y1 power connector pins on the A1 board, they go all the way through the board. That pinout is well documented, maybe we could feed the -12V, 12V, 8.5V, -5V, +5V from a kind of external power supply that uses the backside of the pins (if at least just temporarily, to see if the system otherwise works at all)
EDIT: attached photo of the Y1 pins "all the way through" the board - so you can get to them from either side. Then the corresponding pinout from the IBM MIM manual (there is more elaboration about the DC outs on the next 2 pages after this).



Aside from the fuse below the display, are you aware of any other fuses in this system? I thought at some point I had read about a 2nd fuse, but I'm not seeing any (just the one twist-open fuse at the bottom below the RUN switch).

Yes. You can build a entirely new PSU. Any smallish PC supply should work. Except for the 8.5V which IBM for some weird reason often have in their equipment. But as far as I understand the rating of the 8.5V is not that high so a LM317 with a heatsink and input from 12V should do it.
 
The block diagram is consistent with the pins on the right side (attached photo for reference)
 

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Except (minor point, I think): the block diagram indicates BLACK and BLACK wires going into the DC power supply (along with the green/yellow ground). i.e. the WHITE wire from the Line Cord input on the left transitions into black (per diagram)? But on the physical boards I have, the 120Vac inputs to that DC power supply are 1xBLACK and 1xWHITE wires (the "black" thicker cable is spliced open). Maybe production changes that after the poster was made or I'm just misunderstanding something.
 
@snuci

Got some more time to explain why the PSU "was working" and now isn't.... Here are some notes to elaborate on the three 5110 power supplies that I have, which I'll refer to by these names (and a description for context):

#1 ALPHA My original working 5110 (never opened or disassembled), it is 32K BASIC, no tape drive. This unit is quite dirty inside, very thick dirt on the back of the display CRT and around the PSU area. The expansion cards and A1 board area are relatively clean. Despite the supreme layer of dust (almost mud), this unit fully works, boots to BASIC, shows 32K RWS, and runs fine. So it is a working reference model, which as far as I know no one has "been inside" of it, so all the cable arrangements are original.


#2 BETA For parts 5110 unit, 32K BASIC, no tape deck. The PSU looks complete, but the DC power header that connects to Y1 is missing the header, effectively making it impossible to plug in the connector. [ turns out the header is actually wedged into the Y1 socket, looks like someone pulled it hard and stripped all the 24 wires out -- now the header can't be removed {and attempts to do so and it just crumbles/cracks what is left of that wedged-in header} ]. Table top testing of this PSU resulted in getting the expected DC 12V, 8.5V, 5V on the expected Y1 pins. The caps appear to have been replaced (blue lower profile caps instead of the tall gray ones).

#3 GAMMA For parts 5110 unit, 32K BASIC, with internal tape deck. The display and tape deck appear to be in fairly pristine like-new clean condition. However, the PSU is missing components. Those missing components appear to be in a small bag that came with the unit, but the components are damaged (they look to be cut in half, like someone was investigating what we inside of them). The Y1 power connector is complete (with header). All the expansion cards from GAMMA also work in ALPHA (that's 32K RWS, executive ROS, processor/IO, Display, Language and BASIC ROS -- GAMMA did not come with the Feature ROS, which I do have in my original ALPHA unit).



Initially I didn't think the PSU on BETA was working properly, despite having a very "good looking" PSU. But then I noticed the 3 ground wires inside near the fan area weren't secured. So I secured those, and was then very pleased to then see the expected voltages out of the pins. Since the PSU in BETA now appeared to be working ok, I decided to swap the PSU between BETA and GAMMA. And in that process, I also had to swap the Y1 cable to get a complete cable with header. That is, I had to swap PSUs, but I needed GAMMA to keep its intact DC Y1 cable to use its header. I placed labels on each portion of the cable to ensure I swapped them to the proper headers.


All that went fine, except.... When I powered on GAMMA with the swapped PSU, I saw a very brief spark (on the top left corner of the PSU). I powered the system off immediately. On the top of the PSU (inside with its covered removed) are three cross bar support rails. I didn't fully bolt down the PSU during the test, and so I believe one of those top cross rails touched a component (or was near to it). I'm not sure which one. I believe there was just an electrical flash/spark, I don't think there was any pop or sound. So, since then I've inspected the PSU with a magnifying glass (twice, both sides), and I don't see ANY burned or busted wires or traces, nothing smells burned, all resistors present and intact, caps still look fine, and I just don't SEE any damage.

I did notice that after this mishap, the two brown "thick straw" pieces on the left side of the PSU got extremely hot -- too hot to touch (this makes me believe they are a type of fuse, but they still seem to be intact just fine). I let them cool down for a full day. On the next day, I secured the PSU properly, set all the ground wires (there are 3 ground wires near the fan area, one of them goes to the external connector). And I tried again - the fans come on as expected, there was no spark or electrical odor, and the brown "thick straws" did not get warm (remained cool to the touch even with power on). However, I was still no longer getting 5V or 8.5V out of the expected pins - no DC power coming out of the headers for the Y1 connector (sad, since I confirmed this PSU was giving expected DC outputs when it was installed in BETA.

I put the PSU back into BETA - and same result: was not getting the expected DC voltage values across the expected pins as I had before.

Either I've jarred something while removing/swapping the PSUs, or the brief electrical spark did do some damage.


So that's where I'm at -- I could still pull the working PSU out of ALPHA and use that in GAMMA. OR, I could retrofit the tape deck from GAMMA into ALPHA. I probably won't do either of those, and will wait a while to see if I can come up with another source for -12V, 12V, -5V, +5V, and 8.5V - at least to verify that the PSU is the only issue with GAMMA. I'd love to get a working tape deck going, but I'm trying to leave ALPHA as-is (since it is working and since it has never had any major surgery inside of it).
 
I think the only way to resolve this properly and for the future is to patiently trace out the schematic and document it. Along with scope recordings of all of the important waveforms, to make what would be a complete service manual with a topographical board layout, with a technical description for the power supply and how its sub-circuits work. If this doesn't get done, then it won't help the case of others keeping these computers working across this century and longer. The best scope for the task of documenting the primary side waveforms is the Tek 222ps, which has isolated inputs.

I did this for the IBM-5155 power supply (which also had no manual), to show this sort of thing is possible, the link: https://www.worldphaco.com/uploads/The_IBM_5155_POWER_SUPPLY.pdf

I would do it for this power supply too, but the thing is I don't have a 5110 computer or power supply. So, currently, it leaves it to somebody else to take the time & effort to do it, who will that be ?

Most likely, the large filter supply capacitors on the primary side would still be ok, but the 24 or so ones on the secondary side would require to be renewed.
 
That would indeed be a good idea. But there are seven IBM metal cans in there. Four of them are identical. SLT type with 12 signals. Just a two or three transistors in there. Perhaps a long-tailed pair? The three others are MST type with 16 signals. All different part numbers. These are very likely to be more complex. Perhaps a standard TTL circuit or perhaps something completely different. It will be very hard to understand the design without more information on these three.

If some kind of info could be dug up regarding these three MST cans I am willing to give it a try to reverse engineer it.

BTW. I have gotten myself a HV diff probe now. Nice thing when working with PSUs.
 
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Those MST cans has part numbers 1582779, 1582780 and 1582781. They are marked CTS which I assume is the manufacturer.

The close number range makes me guess that they have related functionality.
 
Those MST cans has part numbers 1582779, 1582780 and 1582781. They are marked CTS which I assume is the manufacturer.

The close number range makes me guess that they have related functionality.
At least if there is one working psu it would be possible to perform a functional analysis on those IBM metal cans, if the inputs & outputs could be identified, which is likely if the schematic was traced out, then they could be scoped & studied. Then at least an equivalent clone circuit could be made to replace them in the case they were defective. Even better if there were defective cans to dissect.

Many years ago I was given an Akai tape deck that was said to be un-repairable because a thick film module in it had failed. I slowly ground off the resin and found it was a device with 5 transistors and a few film resistors and a couple of capacitors. I was able to measure most of the values and the other aspects of it became self evident when I could see the schematic. So these things are possible, depending on how determined you are to find out what IBM put in those metal cans. In many ways, it is a better challenge than the average repair problem.
 
Agree with you there and the more I think of it I think I should do it. Just a schematic with blobs for the IBM cans. One can likey figure out the supply voltages and other obvious things.


But before that I need check if there is some kind of life in the 5110 iself. I.e. Attach some kind of regular PSU and see if it works. Wouldn’t be so fun to have spent eons of time and then the rest of the thing is toast.
 
Agree with you there and the more I think of it I think I should do it. Just a schematic with blobs for the IBM cans. One can likey figure out the supply voltages and other obvious things.


But before that I need check if there is some kind of life in the 5110 iself. I.e. Attach some kind of regular PSU and see if it works. Wouldn’t be so fun to have spent eons of time and then the rest of the thing is toast.
I think it would still be worth it because the results would help others fix their supplies to help keep this line of very interesting computers working. I nearly bought one once, but the shipping to AU was extreme.
 
the shipping to AU was extreme.
Indeed, I recently sold a keyboard (mid 80s IBM one) and a gentlemen from Australia was interested in shipping. I put in reasonable dimensions and weight, and both FedEx and UPS quoted me something near $400 just for shipping (from Texas). I didn't want to insult the guy, but that's really what those couriers were quoting me for just a 20lb package.
 
The following might be obvious to the hardware folks here. But just for reference, I've removed the top cover of my working 5110 PSU ("alpha"). Having worked now with the two non-functional PSUs, I felt OK removing this cover safely. Yes, it's quite dirty inside, this was a 5110 that was *actually* used. I'm not ready to actually remove the PSU (not till I have a verified working backup), but I wanted to confirm/share a couple things (for those who might acquire a PSU that is entirely disconnected and might not know where to begin in putting things back together):

(1) from the backside shown, you can test for 120Vac on two pads highlighted in red. This just verifies the 5A fuse is working, and the "main" components (in the compartment below the CRT) should also be ok.

From there, the "job" of this power supply is to convert that 120Vac into multiple DC voltages out the other side.

(2) It's subtle, but in the image below I marked a green line on the bottom on where approximately the back-side ground wire goes (it is a yellow/green wire briefly visible, then disappears lower below the yellow ribbon cable). There is an elevated screw panel on the external I/O enclosure where that ground wire ties up to.


IMG_1559A_small.jpg





And then also for reference, on the other side if this same PSU: wanted to confirm/verify the WHITE wire plugs in above the BLACK wire. Even if you remove the entire PSU, as long as the 5A fuse below the CRT is present, you'll still get 120Vac out of these two wires (and the fans will spin up). [this is for US-- mine measured about 124Vac].

Also annotated is where the two other ground wires go. The 2nd one tethers towards the external display at the back, while a 3rd is very hidden, but comes up and they both bolt into the GND terminal of the PSU (below and to the right of the copper-coil-thing).


IMG_1558A_small.jpg
 
Also for reference (for "negative" voltage you just reverse the leads, right? )

1650946616950.png



Also for reference: be careful removing the Y1 power cable. I'm not sure what to suggest to make it easier, but don't super-tug to force it out. The 5110 I got arrived like this -- the connector header remains wedged into the A1 board (difficult to remove), and one of the pins is broken off (I think it's one of the 5v's). Not impossible to repair, but will be time consuming. [ the one of the bottom in the image below is "correct" ]


IMG_1566_small.jpg
 
@MattisLind If things work out, I'll be meeting a local hardware engineer over the next week to help repair the 2nd in-tact-but-not-working 5110 PSU that I have (someone I trust and have worked with over 10 years, but on travel presently). After that, for the third one -- I'm hopeless with a soldering iron, so I don't mind offering that PSU up as a sacrifice (as it already has missing components, but the remaining components might be good replacement or can be opened up) if someone is interested in that. Give me a week or so for local to examine first.
 
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