Repair of 5160 XT power supply

[vossi]

Hello,

I have two IBM 5160 from 1985 and 1986 with the 220V "Schrack" 130W supply.
Both have now output at all voltage-lines. I have testes under load condition with a mainboard, cga, floppy-adapter, two fullsize-floppies.
If I switch the supply on, at my postcard only the 12V-voltage-LED lights shortly.
The fans are turning (220V). The fuses are OK. I measured most diodes - they seems to were OK.
In the supplys are no damages visible.

Have someone a hint for a typical failure?
Means the non lighting +5V-LED, that there is the error?
Has anybody a schematic for this supply? - In the technical reference of the XT is it not!

thanks and greets
Christian

 

[modem7]

Welcome to these forums.

A common problem with the IBM 5160 is that a tantalum capacitor on the motherboard goes short circuit and overloads the power supply. You can see how common that is by looking at a list of 51xx motherboard failures at [here].

A procedure for working out which capacitor is faulty is at [here]. Have you tried that?

 

[vossi]

Hi, at one mainboard the C56 had a short circuit and at the other board was a faulty dram-chip.
I changed these - and now both boards are running great with an working power supply.
But both original power supplys are not working...

 

[Malc]

+1 on Modem7's site, Follow the minimum diagnostics procedure and report back.

 

[vossi]

Thanks for support, but I tested with this minimum configuration.
Both mainboards are ok, have no short circuits and works with an other IBM supply from 1984 (made in USA).
The faulty supplys from Schrack (mde in Europe) have both no voltage on all lines. Only the 220V-fan is turning.
The supplys are defenitie faulty, but where can I start to search... are there typical errors?

 

[Malc]

With the PSU powered up and with nothing connected do you still get 0v on all output lines using a DMM to measure the output voltages ?, Could be Cap failure or a short, these old psu's ain't getting any younger, What tools do you have for troubleshooting. Be extremely careful when working on / inside psu's.

 

[vossi]

I measured the outputs with a dmm under load with the working mainboard. I think I have to check all the caps first...

 

[Malc]

Yes Caps are a likely culprit, Also check the X2 Caps, If they are of the RIFA type replace them while you have the PSU apart.

Just an aside, Of the 220v Schrack psu's i have, They all power up and output with no load attached due to the load resistors inside albeit not quite optimal, Though i would expect to see in the region of +11 > -11 > +5 > -5 > V with no extra load attached, If the voltages disappear when connecting a known good load it's more than likely cap failure but of course 1 or more Caps could be totally dead hence your 0V output or a short somewhere. Obviously not all psu's are the same.

 

[vossi]

Today I repaired both 5160 supplys ;-)
In both the 3300uF caps at the 7905 regulator had short cirtcuits!
It's the only cap in the Schrack PSU from this manufactorer - I think it's a bad cap!

greets
Christian

 

[vossi]

In the US 5160 supply from '84 are the RIFA time-bombs. They looked not so good - had some cracks. I changed them with new x2-caps.

 

[tonata]

Hi,

I am restoring an IBM 5160. The power supply was a bit rusty.

The problem:

I think the +12 volts is short circuited with the ground. When I measure it with multi-meter for connection (12 volts and one ground) it beeps continuously. And values are similar to when connecting two grounds.

That is not normal, right? I should not expect when I power it up that this problem will disappear?

 

[modem7]

I think the +12 volts is short circuited with the ground. When I measure it with multi-meter for connection (12 volts and one ground) it beeps continuously.

The fact that your multimeter is beeping, suggests to me that you have your multimeter in the 'continuity' setting. For future reference, note that the continuity setting can sometimes be misleading. See the comment at [here].

In the case of the IBM 5160, the resistance on the +12V line should not be low enough to trigger your multimeter's continuity beep, and so it sounds like there is a problem there.

The problem cause could be on the motherboard, or on an expansion card.

Try the procedure at [here]. If the cause is on the motherboard, then I am expecting that the procedure will have you remove/replace motherboard capacitor C56.

 

[tonata]

Thank you for your response. Yes, 'continuity'.

I am afraid the power supply will damage the motherboard if it not functioning correctly. What are the chances of this happening? I still have not connected the two.

Question 1: Probably a capacitor is responsible for the +12 volts lack of resistance? How should I debug it?

I have also acquired a HEDEN PSX A968 350 Watt power supply with 20 pins and one 6 pin P8/P9 type of connector. It has the 5,12,-12 and -5 volts. I still need to re-wire it to the IBM 5160 specification. I have the P8 and P9 connectors also.

The HEDEN is +5V@25.0A, +12V@15.0A, -5V@0.6A, -12V@0.6A which seems compatible with IBM 5160 power ratings.

And PWR_OK (grey) on the HEDEN = Power Good on the IBM 5160. The green PS_OK (HEDEN) would not be used.

Questions 2: Would this HEDEN PSX A968 power supply be really compatible?

 

[modem7]

I am afraid the power supply will damage the motherboard if it not functioning correctly. What are the chances of this happening? I still have not connected the two.

Damage could result through over-voltage. For example, the power supply generating +6V on the +5V line.

I expect that a decent power supply will contain circuitry to detect an over-voltage situation, and if detected, shut the power supply down.
Some 'cheap' power supplies may not have circuitry to detect an over-voltage situation.

Question 1: Probably a capacitor is responsible for the +12 volts lack of resistance? How should I debug it?

Use the procedure at [here].

I have also acquired a HEDEN PSX A968 350 Watt power supply with 20 pins and one 6 pin P8/P9 type of connector. It has the 5,12,-12 and -5 volts. I still need to re-wire it to the IBM 5160 specification. I have the P8 and P9 connectors also.
The HEDEN is +5V@25.0A, +12V@15.0A, -5V@0.6A, -12V@0.6A which seems compatible with IBM 5160 power ratings.
And PWR_OK (grey) on the HEDEN = Power Good on the IBM 5160. The green PS_OK (HEDEN) would not be used.
Questions 2: Would this HEDEN PSX A968 power supply be really compatible?

You have established that the HEDEN generates all of the required voltages, and can do so at greater power than the IBM XT power supply. You have also established that the HEDEN generates a signal that is the same as the POWER GOOD signal generated by the IBM XT power supply. So, it sounds like the HEDEN will work.

(By the way. If the HEDEN did not generate an equivalent to the POWER GOOD signal, there are ways around that. An example at [here].)

 

[Malc]

....I still have not connected the two........

I'm a bit confused here, When you took those readings, did you take them from the Motherboard +12v - GND connector with nothing connected to the Motherboard ?, Or did you have the PSU on the bench and took those readings from the power connector of the PSU with nothing connected to the PSU ?.

What make of PSU is it, 240v 130W Schrack or ??, Have you powered this PSU up on the bench and checked the DC output voltages with nothing connected to the PSU or with a load connected ?.

 

[tonata]

I'm a bit confused here, When you took those readings, did you take them from the Motherboard +12v - GND connector with nothing connected to the Motherboard ?, Or did you have the PSU on the bench and took those readings from the power connector of the PSU with nothing connected to the PSU ?.

What make of PSU is it, 240v 130W Schrack or ??, Have you powered this PSU up on the bench and checked the DC output voltages with nothing connected to the PSU or with a load connected ?.

I took them with nothing connected. No power from the electrical grid and not connected to the motherboard. A simple multi-meter was used.

 

[tonata]

Damage could result through over-voltage. For example, the power supply generating +6V on the +5V line.

I expect that a decent power supply will contain circuitry to detect an over-voltage situation, and if detected, shut the power supply down.
Some 'cheap' power supplies may not have circuitry to detect an over-voltage situation.


Use the procedure at [here].


You have established that the HEDEN generates all of the required voltages, and can do so at greater power than the IBM XT power supply. You have also established that the HEDEN generates a signal that is the same as the POWER GOOD signal generated by the IBM XT power supply. So, it sounds like the HEDEN will work.

(By the way. If the HEDEN did not generate an equivalent to the POWER GOOD signal, there are ways around that. An example at [here].)

The HEDEN gives 5V after connecting the PS_ON and the ground. So it should be OK. The timings explained on wikipedia are not important I suppose as far as there is 5V at the end.

 

[modem7]

The HEDEN gives 5V after connecting the PS_ON and the ground. So it should be OK. The timings explained on wikipedia are not important I suppose as far as there is 5V at the end.

In theory, there is a timing consideration.

In many motherboard designs, after power-on, the motherboard is held in the reset state for a short period. One of reasons may be the 8088. Its description of the reset pin includes, "The signal must be active HIGH for at least four clock cycles." Other motherboard chips may have their own requirements.

If you look at the Intel diagram at [here], the capacitor and resistor at far left result in the 8088 CPU's reset pin being held high for a short period after power-on. That capacitor and resistor is what IBM used in the PCjr, but in the IBM 5160, IBM chose instead to have RESET controlled by a POWER GOOD signal from the power supply. Therefore, the POWER GOOD signal should not become active until a short period after the 5160 motherboard receives +5V.

 

[modem7]

I'm a bit confused here, When you took those readings, did you take them from the Motherboard +12v - GND connector with nothing connected to the Motherboard ?, Or did you have the PSU on the bench and took those readings from the power connector of the PSU with nothing connected to the PSU ?.

What make of PSU is it, 240v 130W Schrack or ??, Have you powered this PSU up on the bench and checked the DC output voltages with nothing connected to the PSU or with a load connected ?.

I took them with nothing connected. No power from the electrical grid and not connected to the motherboard. A simple multi-meter was used.

I have made an assumption (shame on me) that you are dealing with two problems, a power supply problem and a motherboard problem.

If we go back to your original question, with the subject being a 'continuity' measurement in the power supply between the 12V line and the ground line, then yes, I would not be surprised if the multimeter indicated continuity.

Why do you believe that your power supply is faulty?

As Malc suggested, in case you are unaware, most switch mode power supplies for the IBM 5160 cannot power up unloaded; they need to be adequately loaded. When loading the power supply, you need to use something that is known to be an adequate load, and known to be good. For example, you may decide to use the 5160 motherboard as the load, but what if there is a short circuit in the motherboard. That would overload the power supply, stopping it from working.

 

[Malc]

....If we go back to your original question, with the subject being a 'continuity' measurement in the power supply between the 12V line and the ground line, then yes, I would not be surprised if the multimeter indicated continuity....

Yep, I grabbed a working 240V 130W Schrack PSU and measured the resistance of the +12V - GND line and got a stable 21.6 Ohm's, If i had my meter in continuity mode it would beep as my meter beeps at anything less than 100 Ohm's. Obviously it depends on the PSU manufacture / design.