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Need help. The computerland BC88 is failing!!!

J

JonnyGators

Experienced Member
Joined
Mar 9, 2020
Messages
206
Location
Attleboro, MA
I've really been struggling to trace down this problem. It seems everytime I tinker with this machine, I can somewhat get it stable, and then it sits for a few months, and I bring it back out, and it goes unstable again.

For a while now, I keep periodically running into this problem where the machine just goes black out of nowhere. It randomly strikes, and once it does, it's impossible to make it do anything until I let it sit for a while. Sometimes after sitting for an hour, or hours, it goes back to being stable. But today, I can't seem to get any stability out of it, I'll let it sit, I'll get it on, try to do some tinkering, and it just dies again.

When it happens, the display goes black, the PC speaker makes a blip sound, and that's it. I can turn it off, and turn it back on - the fans and drives come up, the screen goes black (CGA is white when it's off), but no computer activity, no beep of it booting, just dead with a black screen.

Eventually if I reseat the card with the processor on it a few times, or give it some time, or turn it off and on a few times, it will eventually give me the cursor and start booting up, but usually that's very temporary, just gives me the speaker blip and goes black, until I let it sit a long time.


Now, when it was first happening, I noticed that it seemed to happen if I used the red button on the back to restart the machine. I was able to rather consistently prove the behavior - use that button, machine would go black frequently, let it sit, it would come back up and work fine, until I pushed the red button again. So I've made it a rule to not touch that button ever. But now it's happening all the time, and I've not touched that button. I actually desoldered the button today out of desperation just to remove that as a possibility, that has made no change. Seems to go beyond the button.


Whatever the problem is, I need a technical, knowledgeable process to chase it down. Where do I begin? How can I trace down a problem like this?

Also - I'm always on the look out for more computerland BC88 computers, so if by some chance one has one they're looking to unload, do let me know.
 
Sounds like the power supply is failing. As it warms up the voltage drops below the minimum required. Try temporarily powering it with a (more) modern AT PSU (or ATX PSU with adapter).
 
Well, I've confirmed it most likely isn't the power supply.

The problem went away for a while. Hard to measure how frequently it occurs or how frequently it doesn't. But, when the problem occurs, it consistently occurs frequently in a matter of minutes/seconds. And then the longer I let the computer rest, the longer it works before it starts happening again.

But then after a bunch of bursts of that, the computer can also go long periods of time of stability and no problem. I might let the computer rest overnight, next day, use it hours. No problem. Go on for days using it for hours periodically.

Then some time later, I go to turn it on - and it's back to giving me the problems. So today, it started happening again. Right when I finally get the right monitor to pair with it. So, I grabbed my spare new power supply, and put it in temporarily.

I bought one of these brand new from amazon 2 years ago - https://www.amazon.com/gp/product/B0042P2IIG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

And sure enough, the problem still happens with this new power supply.

I suppose it's possible the new one is a dud - but 2 power supplies failing in exactly the same way, one of them being only 2 years old? Unlikely.

The PC speaker makes a blip sound when it cuts out. But also, I think the PC speaker makes a blip sound when powering up - whereas, I don't get that blip when turning it on if it doesn't come on. At it's worst, I can turn the computer on, and get no activity from the start, other than the screen going black.


This computer is very important to me. I will do anything and everything possible to fix this. But I have no idea how to trace the problem any further than this. What do I do?
 
Very strange. I agree it's probably not the PSU then.

I would try running the computer in a minimum configuration. Remove all the cards except CPU and video. It obviously won't boot DOS, but you can let it sit on the BIOS screen or whatever. If it still happens, try swapping in another video card. If it still happens, then you know it's something on the CPU card.
 
I've taken out the hard drive controller and joystick card, that brings it down to it's minimum - PC card, RAM/serial/parallel port card and floppy controller, and video card.

Problem persists.

Will not display anything if I remove the card with RAM, so I cannot strip it down any further.

I tried swapping the CGA card out with a spare EGA card I have kicking around that has worked perfectly fine on this machine. The problem persists. Not the video card.

The other 2 cards are unique to this machine only and are unobtanium. They must be repaired. How do I do this?
 
The behavior you described up the thread could be a component going out of spec when warm. I would use a freeze spray (from amazon, etc, or less costly a compressed air duster spray used upside down will basically do the same thing) to localized spray various components/parts of the board(s) in turn to see if you can snap it back to functionality by doing that. That could help you narrow down to a single failing component.
 
You may have tantalum capacitors that are intermittently shorting and causing the power supply to go into protection mode and shut down.
 
Could be a capacitor, but if the power supply went into protection mode perhaps the fans would still spin, but I would expect everything else to lose power, which would mean hard drive would stop spinning and video card would stop outputting and the monitor would go white instead of remain black. And I don't know that the modern power supply I used would go into that type of protection mode. Usually when you see someone connect a more modern power supply to a computer that has a power supply shutting down like that, you then get to see the bursting of the shorting capacitor, which I think is required for anyone posting a video about restoring a Compaq Portable.
 
When my IBM PC had a "tantrum" capacitor on the motherboard that shorted while it was powered on, the power supply just went totally dead, as if I had turned it off. And I think it may have damaged the power supply because soon after that, it was unable to hold a steady 12 volts. It made me think my hard drive was going bad, because its motor was randomly slowing down and then speeding up again. Replacing the power supply solved the problem. And this reminds me to open up the old PS and see what went wrong with it...
 
Could also be a RAM issue. I had a 486 that would blip and freeze, But that did say Parity Check at the top. Perhaps try it with less RAM, switch the RAM about in the sockets, or look for some that is hot.
 
Unfortunately, I seem to be no closer to figuring out this mystery.

At this point, if I let the computer sit for a number of hours/days, I can get 15-30 minutes of operation. After that, I can only get seconds of operation sometimes.

I've removed all the extra RAM chips to bring it down to 256. That made no change.

I tried using cooling spray to see if that has any effect. At first I thought spraying was temporarily fixing things, but any spray only ever got me seconds of operation, maybe a minute or 2. Which I think had more to do with the time turning it off, maybe reseating the cards, to give it enough of a break to be able to run for a little. After spending a morning spraying portions at a time to try and zero in, I found no portion gave me a long time of operation, and after several power cycles, I'm now at a point where I cannot get it to operate, despite spraying both boards and cooling them both.

Although it seems to be a behavior that suggests something warming up, it seems to not be a problem I can control by controlling the temperature of the boards.

One weird thing - at times when I was turning it off and on, sometimes there's a hesitation of it to turn on. I turn on the power switch, the fans come up, the hard drive starts it's start up sound, and then like a second later there's a pop/blip from the PC speaker, and the curser comes up (detecting the hard drive, and then the RAM test starts). And then after a few seconds, that same PC speaker blip, and the screen goes black. As if there's some sort of on/off mechanism being triggered.

I'm at wits end - this is the most important vintage computer to me, and I cannot seem to come up with any method to find the problem, and it's nearly impossible to replace, and I can only use it for 15 minutes at a time now.

This computer absolutely must be repaired - I'll do whatever it takes - please, someone come up with an option to troubleshoot this machine.
 
I managed to produce a "parity check" error.

I decided another thing I could focus on is the slots of the motherboard. The motherboard is really just a bunch of ISA slots (with some capacitors), the PC is on a card, the ram is on another card, everything is on cards.

This motherboard has plenty of spare slots. The catch is, only 3 of the slots are 8 bit, the others are 16. The 3 cards for this computer, PC card, RAM/serial/parallel/floppy controller card, video card, are all sized so that they will only go in an 8 bit slot, the bottom hangs down that the extra portion of a 16 bit slot blocks the card. Not sure if this was by design. So - I couldn't completely test with different slots, I could only rotate the cards to utilize the same slots in a different configuration.

Doing this, it booted, did the RAM test, went on to run the autoexec.bat file and ask me the date, and then a beep, screen refreshed, and just displayed the text "parity check"

Given the same behavior of a short period of time and random stop, but difference of actually showing me something useful, I think it's the same problem presenting in a different way due to the difference in card configuration. Can't be 100 percent though.

I'm thinking this means bad RAM chip, and just my luck, the RAM chip that goes bad is one of the ones soldered directly to the board? I could desolder, and start replacing them one by one with the spares I took out, to see if I can get it running stable at 256. And then add the others back in and track down a replacement to get it back up to 640k. I guess I have a project today.
 
Please check my work here - I'm assuming parity check errors would be tied to the RAM, but, on PCs of this vintage, is that particular error tied to RAM, or could it be finding an error somewhere else along the way as well?
 
Ok, I'm not convinced the parity check error is significant. Could be - too many variables.

I'm finding that in general, mixing up the cards and slots gives me weird behaviors. In that 2nd configuration where I got the parity check, I tried again and couldn't get it to boot again. Either just a black screen, or would go black, never a second parity check. Not that I tried very long.

Then I went to a 3rd configuration of the cards. It got stuck with the blinking curser never moving on to the RAM test. At some point it booted to ask the date, but it wouldn't accept input from the keyboard, even though the caps lock and num lock lights could be lit on or off utilizing those keys. Tried again, weird color pattern moving on the screen, ctrl-alt-delete, and it rebooted - to a black screen.

Went back to original configuration, back to just a black screen - needs time to rest.


This is just way too random to make any sense out of. I need some real solid, scientific, professional troubleshooting methods. There must be a way people fix these things - why can I not find any useful information online other than random trying of different things and hoping for the best? Someone that knows what they're doing, please......I absolutely must get this computer working again. Please, someone, help me!
 
I'm not familiar with this machine. You say it is a backplane system, with all the RAM on one card and the CPU etc on another. But you said these plug into 8-bit slots. This is normal on an XT (8088), but you said there are 16-bit slots making me think this is a 286. So I'm a little confused. Can you point us to some pictures of this thing. Maybe it is an 8086 system with some odd bus like the AT&T PC.

EDIT: Ok just seen a youtube video about it. Its an XT system on a 286 backplane.

As to your problem. Yes a Parity Check is a RAM issue.

Is the RAM count now smaller? That is, does it reflect the actual RAM in the PC. If it is still counting high then you would need so set some switches somewhere to lower it. If it is still counting high then you will have all sorts of memory errors.

If not, then the error is in the RAM installed on the board, which means you will end up having to desolder it.

EDIT: Because the RAM is on a separate card, It could be the CPU card and RAM card are having trouble communicating, Perhaps spraying some Deoxit on the slots and card edge will help. Also before you start removing soldered RAM you need to have positively ruled out the PSU. Bad power can cause all sorts of problems. Do you have a known good PSU?

Modem7 has a good guide of Piggybacking RAM. You can use this method to sometimes find a bad chip. It is not full-proof though.

minuszerodegrees.net

minuszerodegrees.net
 
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Yes, as you found, the machine is upgradable to a 286, which is why it has the 16 bit slots.

Slots 1, 2, and 4 are 8 bit slots. It came to me with the RAM in slot 1, the CPU in slot 2, and the video card in slot 4. I would guess that's how it was initially.

Yes, while I had the extra ram removed, the boot up process only detected 256K of ram. Since that made no change, I put the chips back in for now, rather than have loose chips I need to keep track of, and it's back to detecting 640k.

In further tinkering, I've yet to make that parity check error come up on screen again.

Given that juggling cards around through different slots tends to have different results, my focus is now on the slots, the motherboard. That seems to make the most sense.

(earlier on this thread we determined it likely wasn't the power supply, testing with a new power supply has the same problems)

While juggling the cards, at one point I had the computer turning on to a cyan screen when the video card was in slot 1. That suggests slot 1 is definitely problematic.

Then I remembered the spare EGA card I have kicking around, which is small and will fit into the 16 bit slots no problem. That at least gets me to a point in troubleshooting where I can leave one of the slots out. So I moved the RAM card into slot 4, things booted up, and after a few minutes of play, click. Black screen.

So I tried swapping the cards.

But - at this point, a new problem has come up, which also happened earlier, but I thought was just due to the card swapping. Now when I get in a bad state, the keyboard stops working. I can get it to boot up, no keyboard - keyboard has power and will light/unlight num lock and caps lock lights. But no keyboard input comes through.


Perhaps problems with slots 1 and 2. And a problem on the motherboard that also inpacts keyboard signal? And perhaps, like you mentioned with CPU and RAM on separate cards, it's a communication issue between the cards that is coming up? I'm not at a point where I feel the next step is desoldering RAM.


At this point, I have to ask - is there a device that will test ISA slots - check for voltages, or shorts, or things like that?
 
JonnyGators said:
At this point, I have to ask - is there a device that will test ISA slots - check for voltages, or shorts, or things like that?
Click to expand...
There are POST cards that have voltage leds on them. You can also use a multi-meter.
 
Ok, I've ordered a post card with voltage leds to at least get a good reading on that. Meanwhile - the keyboard issue was a red herring, there's a connector on the PC card that needs to be connected for the keyboard to work, and moving things around I didn't always get that reconnected.

I've done a lot of playing around today, but I can't help but feel I haven't really learned anything, and I'm still no closer to coming up with any effective troubleshooting for machines of this era. How did people fix these things?
 
Intermittent problems are the most difficult to troubleshoot. You normally try to eliminate components as the problem source systematically, but that's difficult to do if you can't always reproduce the issue.

Since you suspect the backplane, I would start with cleaning out the slots with canned air to remove any dust. Then closely inspect them for bent contacts. Also check the card edge fingers and make sure they are clean.
 
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