iirc it should still post without a battery. naturally, just as soon as I say that, someone will prove me wrong.

They are NEAT machines! I love the one I got recently because of its orange plasma screen. I need to re-cap the floppy drive, but that's a project for "whenever".

If you leave it on for a few minutes then press the F1 key, does it do anything? The screen may just be faulty.

luckybob wrote:

iirc it should still post without a battery. naturally, just as soon as I say that, someone will prove me wrong.

They are NEAT machines! I love the one I got recently because of its orange plasma screen. I need to re-cap the floppy drive, but that's a project for "whenever".

If you leave it on for a few minutes then press the F1 key, does it do anything? The screen may just be faulty.

Well here's the odd thing about this. I can power it up, the power LED comes on, the keyboard lights blink once, the hard drive does its normal seek test, but the HDD activity LED doesn't light up, there's no floppy seek test, nor are any beep codes. I pulled the memory out to see if it would squawk, but nothing happens. What IS odd is that I hear what sounds like the hard drive is trying to read data.

Try plugging in a different monitor. Also a brief google search reveals this unit has plenty of fuses and they like to blow.

I only got a unit like this 2 weeks ago and haven't really learned it yet. You might get some better help over here: http://www.vcfed.org/forum/forum.php?

luckybob wrote:

Try plugging in a different monitor. Also a brief google search reveals this unit has plenty of fuses and they like to blow.

I only got a unit like this 2 weeks ago and haven't really learned it yet. You might get some better help over here: http://www.vcfed.org/forum/forum.php?

Thanks for the info. I tried using an external monitor and still got nothing. I know there is one fuse, and that's for the keyboard, but I think that one is just fine. I am trying to locate others, if they exist. Not looking good so far, but I am not going to give up. This thing deserves to live again.

@brickpad - Once, when I didnt connect the floppy unit on the last floppy connector from the ribbon cable it just wouldnt work even if it had power. It wouldnt make any boot up seek noise. Also sometimes the boot process was slow. Once I moved the floppy unit on the last connector from the ribbon cable everything worked as it should. This was when the floppy unit was single on the ribbon cable.

This problem happened to me also with a WD IDE HDD which was single on a ribbon cable. When it wasnt put on the last connector from the ribbon cable it took ages to boot even if it had the jumpers set correctly.

Maybe you cand see if this is also your case.

Good luck. I'm keeping an eye in the thread to see if you get the BEAST goin' 😁

Robert B wrote:

@brickpad - Once, when I didnt connect the floppy unit on the last floppy connector from the ribbon cable it just wouldnt work e […]
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@brickpad - Once, when I didnt connect the floppy unit on the last floppy connector from the ribbon cable it just wouldnt work even if it had power. It wouldnt make any boot up seek noise. Also sometimes the boot process was slow. Once I moved the floppy unit on the last connector from the ribbon cable everything worked as it should. This was when the floppy unit was single on the ribbon cable.

This problem happened to me also with a WD IDE HDD which was single on a ribbon cable. When it wasnt put on the last connector from the ribbon cable it took ages to boot even if it had the jumpers set correctly.

Maybe you cand see if this is also your case.

Good luck. I'm keeping an eye in the thread to see if you get the BEAST goin' 😁

I pulled the floppy drive and hard drive cable from the board, but still no luck getting it to POST. I have heard that these particular models, most especially the P75, had a nasty reputation for leaking surface-mount electrolytic caps. The strange thing is that this board, at least from what I can see from the top side, does not have surface mounted caps, but all through-hole, and it's clean as a whistle. The planar board (56F9085) appears to be a later revision from what I could find.

I realized on my drive to work this morning, and this might be a bit of stretch, that it's missing the MCA riser card, and may be complaining about that. I doubt this would be the case, but I do know some IBM products are fidgety at times.

I had a look at my P70. I have the older logic board with the 20mhz cpu. I pulled the MCA riser card, and it posted just fine. It did give me an error to run setup, but i'm 99.999% sure it was because I also removed a terminal emulator card and modem.

I was hoping it would be the problem. maybe the new board still needs the riser, but the old one does not.

luckybob wrote:

I had a look at my P70. I have the older logic board with the 20mhz cpu. I pulled the MCA riser card, and it posted just fine. It did give me an error to run setup, but i'm 99.999% sure it was because I also removed a terminal emulator card and modem.

I was hoping it would be the problem. maybe the new board still needs the riser, but the old one does not.

Thanks for the info. I think I might have found the problem though! Have a look at this diagram, and notice F2 (right above PSU). That is a tiny 3A ceramic fuse. I checked it for resistance with my multimeter by placing the probes on both legs, and viola! Infinite resistance (fuse is blown)! Now I need to find a tiny, resistor type 3A fuse. 😎

here you go: http://www.digikey.com/product-detail/en/litt … 26CT-ND/3306918

word of warning, fuses don't typically blow without SOME cause. Be it a short or something else. If I was a betting man, my first guess would be someone improperly installed a card into the slots in the back, causing a short. Mostly because the backplane is missing.

I'd short the fuse with a bit of gum wrapper and see what happens. If something else is fried, it still wont work, but if it was just a fuse, then it should work.

luckybob wrote:

word of warning, fuses don't typically blow without SOME cause. Be it a short or something else. If I was a betting man, my first guess would be someone improperly installed a card into the slots in the back, causing a short. Mostly because the backplane is missing.

I'd short the fuse with a bit of gum wrapper and see what happens. If something else is fried, it still wont work, but if it was just a fuse, then it should work.

A very valid point. I pulled the board out last night for a closer inspection, both top and bottom. I checked all the caps, some of which might be suspect, but they're so small that it's hard to tell whether they're bulging, or just their natural shape. Nowhere could I find any damage to the circuitry, which looked especially clean. While I had the board removed I pulled the BIOS and cleaned the legs and reseated it back in the socket. Once I had it back together I bridged the fuse with a wire with alligator clips, and clamped it to both ends, but still got nothing after powering it up. I don't know if connection was secured or making good contact, but I still think it may have something to do with that fuse. I traced it to the orange wire (Power OK line?) and blue wire (-12v line).

I suspect that, if this fuse is dead, this may be attributed to why there is no brief flickering of any kind from the plasma display when immediately powered on, and no activity from the hard drive LED (even when it's going through its seek test) and floppy drive LED. Only the Power ON LED works.

Another quick update.

Hooked up an external keyboard to the rear PS/2 port. Not sure if the port is strictly for mouse, keyboard, or both, but when I powered on the system, the keyboard LEDs (Num, scroll, caps lock, and power) stayed on.

[Quick update 7-23]

Tested the power supply voltages. These are the readings I've got so far:

+5v line (+4.8v min. to +5.2v max.) = +5.07v
+12v line (+11.5v min. to +12.6v max.) = +11.64v
-12v line (-11.0v min. to -12.9 max.) = -10.64v

The -12v line is slightly concerning as it's 0.36v under minimum spec, or is this acceptable?

I'd defiantly be concerned. pull the power supply and look for bad caps.

That's what I thought (concerning). Won't be fun tearing into that power supply. IBM had this great idea to use POP RIVETS instead of screws! Not a huge problem. I have the proper tools...but still.

yea, you otta isolate the psu and check voltages, if theya re still low, then recap the psu.

luckybob wrote:

yea, you otta isolate the psu and check voltages, if theya re still low, then recap the psu.

I probably should have disconnected everything first now that you mention it. I only disconnected the block connector that goes to the planar board. When I checked the tolerances they are in spec according to that datasheet, except for the -12v line. Not sure if that's a cap problem or a voltage regulator?

In experience, regulators are typically all or nothing. bad caps is MUCH more likely.

luckybob wrote:

In experience, regulators are typically all or nothing. bad caps is MUCH more likely.

Well that should makes things a little easier (hopefully). I've got the power supply pulled and ready for disassembly. I'll get plenty of pictures to document the process, and hopefully a reference point for anyone in the future who has one of these systems.