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Motherboard repair required - NEC powermate 1

rheffera

Member
Joined
Jan 5, 2014
Messages
27
Location
Adelaide, South Australia, Australia
Bought a NEC powermate 1 a while back that had some motherboard issues and then died. Description as follows:
640kb base, no ext.
(in order of events)
- keyboard seemed to be VERY sensetive about being plugged in (it was fully in but for some reason woudnt pick it up unless certain angle). I pegged this to the solder on the socket
- Random hanging
- I then ran topbench as it audibly clicks the pc speaker so i knew when it hang. It hanged after a few minutes with a NMI
- A20 gate failure started appearing on boot
- Complete failure. No video out, No POST

Good things ( that may help narrow the issue)
Memory always passed self test.
No issue with any of the ISA slots
Extended memory passed tests (when it was in the machine before i pulled it to see if it was an issue)
Was booting from XTBIOS via NIC + ISA BRIDGE + SD card
All DIP switched on the board appeared to operate correctly
Power supply is fine. Was tested on a powermate 286 board.

I suspect definetley the keyboard controlelr, but as to why it hanged / died alltogether is a mystery

I would describe the board as reasonably clean for its age, some very light corrosion (percieved as "roughness") on the top of clock crystals. all text intact.
no obvious patches(brown horrors) of corrosion of the board or corrosion of solder joints. i would some areas of the internal chassis as the same "rough" feel...light corrosion

Pins on chips appear to be fully intact

I would very much like for someone to repair this motherboard if possible. I lack all the electronics related equipment.
More than happy to send this board anywhere on this planet to be fixed.
'I have a VERY strong sentimental attachment to this model as it was my very first computer, as such i would really like this motherboard repaired, and the unit back in use.

Find a large photo below

IMG_20150109_230721.jpg

For some reason the photo makes the board components more corroded than they are. those clock crystals do not look like that on the real deal, and he 74* series logic chips are perfectly legible in the flesh
As such, a cash reward is offered for her salvation. Name a price.

http://museum.ttrk.ee/th99/m/M-O/31487.htm
 
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I could help you out, but a few considerations:

1. Would have to ship the power supply as well - its proprietary...
2. Would be able to reflow the solder on the entire board, would eliminate *ALL* cold solder joints :)
3. I've got a POST card, so hopefully it's alive enough to tell what's wrong with it.
4. For the most part a bad keyboard controller wont prevent the system from posting, have you tried just pulling it out?
5. If one of the "CHIPS" chips is bad, might be real hard (or expensive) to find a replacement. 98% of everything on the board is handled by them.
6. The order of events would point to a bad cap (or two or three), except a bad cap wouldn't really cause it not to post... Perhaps the bad cap is triggering the power supply's over current protection? have you verified that the power supply stays on?

If you want to discuss me looking at it, let's take the conversation to PM.
 
I suspect definetley the keyboard controlelr, but as to why it hanged / died alltogether is a mystery
I would as well. Since the keyboard controller also controls the A20 gate, it's not really a mystery why it hanged. It may have switched the gate randomly, which would crash the system.

Anyway, since the keyboard controller is a standard part, have you tried with a working one?
 
I could help you out, but a few considerations:

1. Would have to ship the power supply as well - its proprietary...
2. Would be able to reflow the solder on the entire board, would eliminate *ALL* cold solder joints :)
3. I've got a POST card, so hopefully it's alive enough to tell what's wrong with it.
4. For the most part a bad keyboard controller wont prevent the system from posting, have you tried just pulling it out?
5. If one of the "CHIPS" chips is bad, might be real hard (or expensive) to find a replacement. 98% of everything on the board is handled by them.
6. The order of events would point to a bad cap (or two or three), except a bad cap wouldn't really cause it not to post... Perhaps the bad cap is triggering the power supply's over current protection? have you verified that the power supply stays on?

If you want to discuss me looking at it, let's take the conversation to PM.

For some reason i am unable to see a link to PM you nor able to create one manually "Insufficient privileges" this is strange as i was PM'ing fine early last year "

As for the power supply, i lack even a multimeter so i cannot confirm that the board is receiving power. All i can say for sure is its fan still runs. Multiemters are cheap enough, $10, so i might just nab one and find out for you.

Now that i think about it, just before it died it intermittently failed to post. That is to say, on power on it appeared as it does now. Dead. Power was cycled and it was alive again. What i might do is obtain one of those POST cards & multimeter and get back to you with results from those.
 
On closer inspection of the board i have noted a few trouble areas i previously missed.

IMG_20150111_101251.jpg
IMG_20150111_101404.jpg
IMG_20150111_101431.jpg

A leaky clock, Fairly corroded clock, and our keyboard controller (YAN25D05) has a pin that has corroded off.

I'm lifting the 8042 from my powermate 286 and putting it the powermate as we speak, but i dont have high hopes as i think other issues are preventing it from POST
 
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AHA! She posts! ( i had the 8042 in the wrong socket), however the board certainly still has issues and needs to be looked at.

I am using one of those PS/2 - AT converter plugs.(THis worked fine initially as i woudnt have been able to verify XTIDE functionality) All mobo jumpers set to default.

Out of 7 Power Cycles, 6 POST's Without keyboard connected:

1x Hang (as below)
IMG_20150111_114508.jpg
1x Failure to POST ( So it still has issues..)
4 x Keyboard Failure
1x keyboard failure, followed with self-reboot

With keyboard connected (it should be noted that the failure in keyboard lights ALWAYS flash, but only dimly) Out of 5 boots:
2x Keyboard clock line failure (as below)
IMG_20150111_112812.jpg
1x Keyboard failure + memory error
IMG_20150111_114253.jpg
2x Normal POST Sequence ("Strike F1...") But the keyboard is unresponsive

That leaky clock is the closest to the keyboard, i suspect it. I would replace that corroded one as well.
 
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