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p70 no post?

H

harry

Experienced Member
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Oct 19, 2007
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While adhering to the stay at home rules, I decided to dig out some older projects, among these, the IBM P70 portable seemed like a good idea. I knew the floppy drive needed attention, but as I recall was otherwise working , I switched the P70 on and was greeted on screen with usual error codes, but otherwise seemed ok. I left it on for about 5mins while I checked over the already removed floppy drive. Turned it off for approx 5mins, when I turned it back on, this time nothing on screen, no beeps, hard drive spinning, green power-good led on, but no post?
I have been searching for tips on this, and it seems a problem with no easy fix. The tech manual's advice .. "Replace system board". I have removed, cleaned the system board, reseated all, cleaned up everything, I have now come almost to the last idea that maybe the roms are the cause, if not maybe the CPU , AFAIK, at power on, after the power good signal, the Bios roms first check memory, if ok, the rom bios code is loaded into memory. I have removed, and swapped the simms around, and even tried to boot with no memory, just to see if it will respond or complain with some beeps, but nothing? All psu dc outputs to m/b and plasma screen supply are very good, well within spec.
I do have some 27512 eproms, and if anyone can help or direct me to the two bios rom codes,( ROMs 65x1565, 65x1566, if their codes are in fact available), I can try to burn new roms. Any other ideas, or resolves much appreciated.

Harry
 
check the outputs of the power supply?

I kn ow its more of an issue with the P75, but the aluminum bodied capacitors in these machines can leak. To make matters better, not only can bad caps cause the system not to work, they can leak a corrosive liquid all over the boards in the system.

so I'd check the state of the caps, maybe it needs a recap? especially if the machine had been sitting for a long period, then was powered up for awhile and everything got up to temperature, and caused any caps that were questionable to go all the way bad.
 
I had removed the system board and examined all, everything appears to be in very good clean condition, obviously not the case, as something is wrong, there are only a few electrolytic caps on the board, and although none show any signs of leakage,or corrosion,replacing them should be no problem, but I hate having to unsolder and replace things without reason. I guess a good reason is that it does not work as it is! So yes maybe I will recap it and see if the board will show any signs of life.
Meanwhile if anyone can help with the two bios rom codes, that would be great. Was it really such issues with these ps/2 machines, and others, that system boards were just simply replaced, not repaired at component level ? Must have been a lot cheaper, and quicker to replace a board rather than spend time fault finding. I assume replaced boards were eventually sent back for refurb, and testing, or just scrapped .

Harry
 
I highly doubt it's the BIOS ROM(s), they're not easily messed with and are the OTP type, unlike later Flash-based PS/2s. If, for whatever reason, the RTC/CMOS has be corrupted it can take an inordinately long time for both the P70 and P75 to begin a memory count, after having tried to work out a basic configuration. Turn it on, leave it alone for 15-20 minutes and then see what status lights you have, leaving the RefDisk in the FD would be a good idea, to get a halted screen display to prove it's working.
 
Thanks WBST for your suggestion, I assembled things and left powered on for just over 45mins, but nothing changes, no beeps , nothing on screen, I am still trying to figure out the boot sequence, and not much luck reading or understanding the tech manual for help, if the power good signal initiates the start up sequence , this should be the start of post, but there appears to be many things that can stop the machine from progressing? I have checked the outputs from the psu and all dc voltages are good,the 5V power-good signal is there. will the corrupt cmos stop post from happening? Should I be able to check if the memory is actually being tested at power on? Not much in the way of schematics, repairs, or testing of these ps/2 machines so any help on what I can test for next most welcome.
 
WBST said:
I highly doubt it's the BIOS ROM(s), they're not easily messed with and are the OTP type
Click to expand...

The P73 are CERDIPs. I do have the late, single EPROM image, but since the OP mentions both, I'm not sure I have the BINs.
 
harry said:
older projects, P70..already removed floppy drive.
Click to expand...

I gave away my four P70s and I never looked back...

Do you mean that the floppy was removed, serviced, and re-installed previous to the recent power-on?

nothing on screen, no beeps, hard drive spinning, green power-good led on, but no post. Wow, you know how to go for the gold...

WBST, the system should give at least one beep if the system was good. More beeps if something wrong.

Waited about 5min to restart, should be good, some systems would get confused with a quick power-off / power-on....

Speaker plug connected? No video happens a bit, WBST is your Huckleberry...

HD spins? Power Good LED? Usually, if it is a power related issue, like poorly seated SIMMs, poorly seated MCA adapters, badly seated drive cables, the system doesn't spin up.
 
Tim, do you wandt your Micro 2000 POST Probe?

That boat anchor of an S100 is gonna stay here for a bit.
 
nothing on screen, no beeps, hard drive spinning, green power-good led on, but no post. Wow, you know how to go for the gold...
Click to expand...

yep thats it but no Gold!

I have now stripped the psu,( what a design ) cleaned all, replaced most all the small accessible caps, not that any looked suspect. left it on the bench running the main board in situ, checked all low outputs with scope, (not the plasma feed, the dvm shows 200v dc.) If I remove the main board again should I definitely get a beep/ beeps from the speaker when I power on with just going back to basic setup, with bare board no add-on's? with or without simms?

Harry
 
harry said:
I have now stripped the psu,( what a design ) cleaned all, replaced most all the small accessible caps, not that any looked suspect. left it on the bench running the main board in situ, checked all low outputs with scope, (not the plasma feed, the dvm shows 200v dc.) If I remove the main board again should I definitely get a beep/ beeps from the speaker when I power on with just going back to basic setup, with bare board no add-on's? with or without simms?Harry
Click to expand...

Goldfinger...

So you can try breadboarding it on a non-conductive surface. Cardboard or wood. This is to czech for life. Leave the floppy, two slot riser, video card, hard drive unconnected. Make sure the speaker is connected! Use one SIMM in POS1. You need at least one SIMM to POST.

OBTW, what FRU is your SIMMs?

Power on [Captain Power and the Soldiers of the Future!]
 
harry said:
I have now stripped the psu,( what a design ) cleaned all, replaced most all the small accessible caps, not that any looked suspect. left it on the bench running the main board in situ, checked all low outputs with scope, (not the plasma feed, the dvm shows 200v dc.) If I remove the main board again should I definitely get a beep/ beeps from the speaker when I power on with just going back to basic setup, with bare board no add-on's? with or without simms?Harry
Click to expand...

Goldfinger...

So you can try breadboarding it on a non-conductive surface. Cardboard or wood. This is to czech for life. Leave the floppy, two slot riser, video card, hard drive unconnected [indicator leds not needed]. Make sure the speaker is connected! Use one SIMM in POS1. You need at least one SIMM to POST.

OBTW, what FRU is your SIMMs?

Power on [Captain Power and the Soldiers of the Future!]

http://ps-2.kev009.com/ohlandl/8573/8573-P70.html
 
I removed the main board again, and was going to set it up on the bench, I then thought I should have checked the board for shorts /leaks across the supply inputs to ground, and there it shows 130 ohms across the 5V rail to ground? there are 7 capacitors on the board across 5v to ground, so I changed them all, still the same? time to call it day I think, I have various other boards from equipment, all with faults on the 5v to ground. and finding such faults, with so many components on the 5v rail must be nearly impossible, for me at least. A parts machine may turn up.
thanks for all kind help
Harry
 
Time for a little thought. A replacement system board might not do, after 20 plus years in storage, no idea if they were removed for errors, I dinna ken. I have no P70s at all, so I can't test the spare dual EPROM P70 system board. It is an option, but desperate choices for desperate times...

WBST, where are you?
 
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