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Compaq Portable working, but with strange issues

I

IlikeTech

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Jul 3, 2017
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45
Location
Maine, US
Hello!
I recently acquired a Compaq Portable, and after replacing the two shorted (0.0 ohms) tantalum capacitors on the mainboard, the machine boots. I also cleaned the floppy drives. Now, here's where the strange things begin. The machine will not boot if it was just turned off, and this is a power supply problem, because it happens even with the motherboard disconnected. If the machine was running, and I wanted to reboot it, If I toggle the power switch off and back on, nothing happens. The power supply just won't restart. However, if I leave it for a minute or two, the power supply will work and the machine will come to life.

This leads to the other issue. If I reboot with CNTRL-ALT-DELETE, it won't boot from the floppy it was happy running from before. It will just spit out diskette errors, and it doesn't sound like the drive head is moving at all. If I let it sit off for a while, it will go back to reading disks. Also, it will continue to work booted up, as long as I don't try to replace the floppy in the A drive. If I do, it stops reading as well. I'm thinking their may be a bad cap somewhere that's causing havoc.

After I replaced the shorted caps, the resistance of the board went to an almost infinite number of ohms. However, on the rails without shorted caps, there's one that is around 300 ohms. Should I replace those tantalum caps as well?

The machine had a multi-io card in it, and I can't seem to figure out what it is. It has RAM on it, as well as a RTC and serial and parallel ports. Attached is an image. Does anyone know what this card is/know what it's jumper settings are? I want to reconfigure it's ports.

Thanks!

e1D69u9.png
 
IlikeTech said:
After I replaced the shorted caps, the resistance of the board went to an almost infinite number of ohms. However, on the rails without shorted caps, there's one that is around 300 ohms. Should I replace those tantalum caps as well?
Click to expand...
When you measure the resistance of a voltage line/rail, you are making a parallel measurement all of the components on that line. The +5V line has lots of components (mostly IC's) on it. The +5V line measurement that I have done of many good IBM 5150/5155/5160 motherboards varied considerably, but was a low as about 200 ohms on at least one motherboard. So, about 300 ohms may be normal for your particular motherboard.

IlikeTech said:
The machine had a multi-io card in it, and I can't seem to figure out what it is. It has RAM on it, as well as a RTC and serial and parallel ports. Attached is an image. Does anyone know what this card is/know what it's jumper settings are? I want to reconfigure it's ports.
Click to expand...
That card looks very familiar, so familiar that I think I have one somewhere. I will take a look.
 
Thanks for the information and for looking for that board. It used to have a NiCad battery as well, which I desoldered.
 
That card looks like a Diamond Flower, Inc card. The model shown on TH99 has only a header for the game port:
https://th99.infania.net/i/C-D/52500.htm

It is not uncommon for these kinds of power supplies to require perhaps 10 seconds or so before cycling the power back on, but over a minute is excessive.

The drive issue sounds to me like the drive may just be dirty. Id pull it out, check the rails and the track zero sensor. Good idea to clean the heads while at it. Also make sure the disk you are using was not written with a 1.2mb drive. If the problem continues, it might be worth trying to power the drive using an external power source just to rule out power supply issues.
 
Those jumper settings worked great! The portable is now up to 640k! Also, I may just have been being impatient with the power supply. It only takes about 15 seconds of sitting for it to work again, which seems normal. The 12 volt rail is at 12.3 volts though, not sure if that’s too high.

I swapped the A and B drives, and now the system boots all the time, and the B drive has issues, so I’ll give that drive a clean. It appears to be giving me a not ready error.

Would it be possible to put in an Ethernet card to transfer files? I only have 16 bit cards.

Thanks!
 
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I have a few portables and the power supply is designed to act like that.
From Sams Photo Fact's;
power.jpg
 
Thanks for the tip about the power supply! I swapped the B drive with another one for a test, and it’s working, so I need to work on the other one. I also got the ram and serial card configured, and got the 8088 MPH demo working!

I gotta get a XTIDE, as dual floppies are miserable.
 
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