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PS/2 30-286 video fault

T

tezza

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Hmmm...My PS/2 30-286 seems to have developed a video fault. I left it running for a while recently and when I came back the monitor was showing no signal from the machine. Every time I turn it on, I can't get a signal to the monitor. It's as if the monitor is not connected.

I've checked the cables and plugs. They are ok. I've also plugged in another monitor. Same result.

Any ideas?

Tez
 
Have you looked into the video section in the machine for something burnt? Smell anything funny?
 
No, no smell of burning capacitors.

There has been a further development. When this first happened, I could still hear the machine boot (floppy disk light come on, drive would clatter, then go off...hard disk would then clunk away). However, now even THAT doesn't happen. On applying power, the hard disk spins up then ...nothing happens at all?

Doesn't look good. I've tried reseating the chips that were socketed. I've also removed the two RAM pairs at a time to see if I could isolate faultly RAM. No difference.

Googling for a technical manual might be the next step.

Tez
 
OK, I've got the IBM PS/2 Hardware Maintenance Manual (1994).

I'll see what I can do with that. I have a feeling this might be unrepairable though as if there is no display, the suggestion is to replace the motherboard and see if this fixes it!

I've got power suppy voltages now though, so I can at least check those.

Tez
 
modem7 said:
Are the voltages (and 'power good' signal) from the power supply good?
Click to expand...

I'll check them tonight. Are you able to tell me how you check the "power good" signal though? I'm not familiar with what that is.

Tez
 
Power good

Power good

Page 138 of that 1994 IBM PS/2 Hardware Maintenance Manual shows the power connectors. The 'power good' signal is on pin 1 of P3.

What is the 'power good' signal? When the power supply is turned on, it takes a little while for the voltages to get to the correct level and stabilise. You don't want the motherboard to be operating during that time. The 'power good' signal is the power supply indicating to the motherboard that the power supply has stabilised (ie. "you're good to go"). Technically, it takes the motherboard out of the reset state.

Expect to measure +5V on the 'power good' line.

Don't fall for the trap of trusting the 'power good' signal. By that I mean, if you measure +5V on the 'power good' line, don't assume that power is good and therefore that you don't also need to measure the +/- 5V and +/- 12V lines.
 
Hmm..well, that's been interesting.

I've discovered my IBM Model 30 286, is actually a Model 25 286, which was released 3 years later (in 1990) than the former! (Why IBM would give a LOWER number to a later model is beyond me? How confusing!)

I discovered this when I looked at the power connectors, which were a 12 pin bank and labelled P7! As the chip is definitely a 286 is must be this model, to correspond to the power lead diagram in the manual.

Anyway, in testing the power, the leads show - and + 12 and 5 volts where they should BUT the "power good" line only shows +0.32 volts? Does this mean the power is "not good"? If so, it would explain why the motherboard doesn't seem to be firing.

Does it need a load or anything to show the correct voltages?

Cheers

Tez
 
Last edited:
Anyway, in testing the power, the leads show - and + 12 and 5 volts where they should BUT the "power good" line only shows +0.32 volts? Does this mean the power is "not good"?
Click to expand...
Yes, at least according to the power supply. So here are the possibilities:

1. FAULTY POWER SUPPLY
The voltages could be in tolerance but the circuitry that generates the 'power good' signal is bad.

2. FAULTY POWER SUPPLY
The voltages are out of tolerance when under normal load.

3. FAULTY MOTHERBOARD
Motherboard is overloading the power supply, dragging down one of the supply voltages.

4. FAULTY OTHER DEVICE
Eg. Diskette drive, hard drive. That faulty device is overloading the power supply, dragging down one of the supply voltages.

Does it need a load or anything to show the correct voltages?
Click to expand...
No because the power supply will be regulated (unlike say an unregulated power pack).
Some power supplies need to have a load though in order to turn on. I know that at least some of the PS/2 power supplies don't need a load in order to turn on.

So I suggest that you try powering up without the diskette and hard drives and see if anything appears on the screen (ie. quickly eliminating possibility #4 above).
If there's still nothing on the screen, reconnect everything then let us know what the actual voltages you measure on the +/- 5V and +/- 12V lines are.
 
modem7 said:
Yes, at least according to the power supply. So here are the possibilities:

1. FAULTY POWER SUPPLY
The voltages could be in tolerance but the circuitry that generates the 'power good' signal is bad.

2. FAULTY POWER SUPPLY
The voltages are out of tolerance when under normal load.

3. FAULTY MOTHERBOARD
Motherboard is overloading the power supply, dragging down one of the supply voltages.

4. FAULTY OTHER DEVICE
Eg. Diskette drive, hard drive. That faulty device is overloading the power supply, dragging down one of the supply voltages.
Click to expand...

I tested the power supply when it was detached from the motherboard, so I guess that points strongly to number 1, correct? I'm assuming if "power good" is sitting at 0.32v it will never fire the motherboard? Certainly this is the symptom now when plugged in. The mother board appears dead.

Originally though, the motherboard did fire (you could hear a boot sequence taking place), ..it was only the video that was absent. Now there is nothing though.

I strongly suspect that there is something wrong with the power supply. Although the 12v and 5v lines appear normal without a load, perhaps initially the motherboard load caused these voltages to go out of tolerance (hence causing the video problem) then something else failed and the "power good" circuitry also malfunctioned leading to the current situation.

Does this sound like a fair assessment?

Tez
 
tezza said:
Hmm..well, that's been interesting.

I've discovered my IBM Model 30 286, is actually a Model 25 286, which was released 3 years later (in 1990) than the former! (Why IBM would give a LOWER number to a later model is beyond me? How confusing!)...
Click to expand...
No, the Model 25 286 and Model 30 286 share the same planar. There is two different versions, just variations of the EPROM BIOS chips and VRAM. The Model 25 stuff did follow the Model 30 slightly (8086 and 286 versions, then there was a 25SX model that wasn't replicated on the Model 30 side), and sometimes the 25 level did a little more as a result.

tezza said:
Hmm..well, that's been interesting.
Anyway, in testing the power, the leads show - and + 12 and 5 volts where they should BUT the "power good" line only shows +0.32 volts? Does this mean the power is "not good"? If so, it would explain why the motherboard doesn't seem to be firing.
Click to expand...

The pin order is the same as the PC/XT/AT, just a smaller connector. I do remember there was some reversal of the "Power Good" signal. Pity your location; I have PSUs and planars aplenty for these things.
 
tezza said:
Does this sound like a fair assessment?
Click to expand...
No. The motherboard can be equally at fault.

Don't be too fussed about previous symptoms - just look at the symptoms as they are now. When repairing stuff, pick a symptom then establish the cause of that symptom, then fix the cause of the symptom. Often, fixing one symptom will correct the others (if any).

IBMMuseum said:
I do remember there was some reversal of the "Power Good" signal.
Click to expand...
Well, this throws a spanner in the works. Can anyone confirm/deny that the 'power good' signal is opposite to the norm in a PS/2 model 25-286 ?
The 13th edition of Mueller's Upgrading & Repairing PCs (2002) postdates the Model 25-286 and the section in there on 'power good' indicates an active high signal. It makes no mention that some power supplies have the signal active low, which would be a very significant fact to omit.

So I suggest that you try powering up without the diskette and hard drives and see if anything appears on the screen (ie. quickly eliminating possibility #4 above).
Click to expand...
Did you try that?
 
modem7 said:
Did you try that?
Click to expand...

Yep, I started it up with the drives disconnected. Same symptoms.

After that, I also plugged the PSU into the board, but didn't push the plugs fully home. They were connected but the bottoms of the pins were exposed. I (carefully) measured the voltage and got a - 12V and a + 12V on the pins I should have (3 and 4) and a -5v and + 5v on pins 9 and 10. I couldn't reach pins 11 and 12 as a tab was in the way.

I've attached some pics of the unit. I'll be grateful if anyone can tell me exactly what this model is. There is no label on the case that specifies one.

Tez
 

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modem7 said:
Any numbers like 8525-006 (format of XXXX-XX) ?
Click to expand...

Ah ha! Right on the bottom right corner under the bevel is a lable and a serial number. The label says 8530-F21.

That would suggest a Model 30. However, not 8530-E21. It definitely says -F21 although I can find no reference to this submodel on the web. It looks like a definite F, rather than an E with the bottom horizontal faded.

Certainly, it doesn't have the same power connectors as the Model 30-286 as shown in the PS/2 Hardware Maintenence Manual?
 
modem7 said:
Model 25-286 board at http://ps-2.kev009.com:8081/ohlandl/8525/8525-286_Planar.html
Model 30-286 board at http://ps-2.kev009.com:8081/ohlandl/8530/8530-286_Planar.html

Per IBMMuseum's statement, same board.

Your EPROMS are dated 1988. If you look at http://mastodonpc.tripod.com/ibm/model.html, the early model 30-286s (8530-E01 and 8530-E21) were announced in '88.
Click to expand...

Well, looks like it is a Model 30 286 after all then. Certainly the specs look right. Maybe the stamp that made the lable had a faulty E letter, because there doesn't seem to be an F21 in any listing I can find. Unless it's a submodel specific to Asia, Australia and the Pacific, which is always a possibility I guess.

Tez
 
J14

J14

J14 is another power connector (that the 1994 PS/2 Hardware Maintenance Manual doesn't mention). The black wire will be ground, the two reds are bound to be additional +5V. What does the brown wire measure at?
 
modem7 said:
J14 is another power connector (that the 1994 PS/2 Hardware Maintenance Manual doesn't mention). The black wire will be ground, the two reds are bound to be additional +5V. What does the brown wire measure at?
Click to expand...

I'll check it tomorrow and let you know. Thanks for your help so far.

Tez
 
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