Reviving Compaq 8088

[ScutBoy]

I'm trying to do a revival of a Compaq 8088 desktop machine for a friend, who would like to see what (if any) data can be recovered from the hard drive.

The power supply on the machine was bad. I sourced a replacement (the one with the single ribbon cable that connects to the logic board) and now when power is applied the LED on the front and the two LEDs on the keyboard flash once every second.

The hard drive makes a clicking noise as well in sync with the LEDs

There's no other noise/beeps, and there's no sign of life on the attached monitor (the one with the funky 3 pin DIN power connector).

I tried disconnecting the hard drive and floppy drive to minimize power load, but that made no difference.

I have not yet pulled the board out to see if there's anything obvious. I thought I would check here with the collective in the meantime if anyone has some previous experience with this old guy.

I assume another angle of attack would be to put the hard drive in another machine and try and bring it up there, but currently I don't have anything else with a suitable ISA controller card.

 

[SomeGuy]

Can you actually tell if it is the power that is going on and off?

To protect it, I would not reconnect the hard drive until that is sorted out.

Unfortunately, that only leaves the motherboard and CRT/analog boards as suspects, although I'd question if that new power supply was really working properly.

Not certain what the absolute minimum is required to get the power supply to start up on this machine, but on a normal power supply, I'd try it with nothing but spare hard drive attached. Also keep in mind some early power supplies won't start up or may even be damaged without sufficient load - but no idea if this power supply is like that.

If the concern is to retrieve data from the hard drive, what I would do is just pull the hard drive and the controller (you have to use the same controller), and plug those in to a known working PC. Then quickly back up the data.

 

[jafir]

I think the video card in these is a pretty common failure. I got my Deskpro with no VDU in it at all, and I'm guessing that it was harvested to repair another computer, or was removed because it was bad. I put my "spare" compaq portable VDU in it, and it wouldn't work. Turns out my spare was bad too, when tested in my portable it wouldn't power up. I've got a known good EGA card now, that works in my portable and has settings for the deskpro, so I need to dig the thing out to test is again.

I think "The 8 bit guy" had some issues with VDUs is his portable as well.

 

[resman]

As always with these old machines, check the motherboard for shorted caps. Usually near the power supply connector.

 

[JJF]

If it were me, I would pull the board and the and work on it on large anti-static bag or an anti-static surface. Models 1 through 4 were 8-bit ISA. So almost any CGA card will work, but if the CGA card has switches or jumpers they must be properly set. Note that CGA won't work with most new monitors, so some sort of a CGA to VGA adapter is needed.

The first step, others have mentioned, is to examine tantalum power supply capacitors, These are the yellow or orange blobs located within a few inches of the power connector. there are five of them. The typical failure is a shorted circuited capacitor that drags down a particular power rail. A shorted capacitor will usually look pitted, and/or black in spots or have burn marks. The power supply is heavy enough to have burned to burn the cap.
if you find one or more burned caps, replace them good quality 25 vdc tantalum. Don't go with 16 vdc caps or you will likely do this all over again. From my experience, Amazon is not the place to by tantalum caps. For test purposes, a bad power cap can be removed from the circuit. Simply cut one lead.

Step two is to make sure the power supply is working. if the power supply fan goes up and down in speed, there is a problem probably motherboard caps. Turn it off but watch for smoke; a good indicator of the bad part. If you look at the edge of the motherboard where PS connects, the appropriate voltage for each pin is marked. Take a piece of paper and draw the connector with the pins and voltage markings. Now, I don't know how the computer/power supply "power good" circuit works so let the motherboard do that work. And since you have already had the power supply plugged into the motherboard, you probably won't do any more damage by by connecting the power supply to the motherboard again. Push the power supply connector onto the pins but don't fully seat the connector. Leave 1/8" of an inch space; just enough space that you can get the probes of your volt meter to the power connector pins. here is where thing get tricky: There will be several (4) pins marked "GND". Touch and keep the negative, ground probe to one center of the group of 4 with out touching any other circuit part.. Then touch the positive probe, one pin-at-a-time to +5v, + 12v pins. Then swap the probes around and touch -5v pin. if the voltages checkout then Tantalum caps and the power sully are OK. Be sure to turn the power supply on before doing this test.

Step 3 is to plug a known working video card into the motherboard an a monitor into the video card and see if the motherboard successfully POSTs. make sure the switches are set properly for the test configuration. The board may post with codes 301- keyboard not attached, 401 – printer not attached or 601 floppy not attached. That's OK. But 201 is a memory error and that's not ok. try replacing the indicated memory chips. if the the board does not post, well, i have exhausted my knowledge base. Check eBay for a replacement board.

Typical configurations:

Model 1 4.77-7.14Mhz, 8086, 128Kb RAM, 1 FDD
Model 2 4.77-7.14Mhz, 8086, 256Kb RAM, 2 FDD
Model 3 4.77-7.14Mhz, 8086, 256Kb RAM, 1 FDD, 10Mb HDD
Model 4 4.77-7.14Mhz, 8086, 640Kb RAM, 1 FDD, 10Mb HDD, 10Mb Tape Drive