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Need help. The computerland BC88 is failing!!!

I recall an issue where I blew out an inverter (or nand?) chip connected to the bus, that was causing parity errors, let me look up the old schematics. Do you have schematics for your computer? It was something to do with NMI and parity errors, but this was an ibm 5150.
 
The ISA test card arrived. And is not as useless as I feared it might be for a computer of this age.

I noticed upon putting the card in a slot, 7 leds lit up. And then when the problem presented, the 8th led lit up.

The 8th led? Reset.

Which brings us back to how the problem initially presented itself - used to be that if I dared use the little red reset button on the back of the computer, it would frequently go black like that until I let it sit for a number of hours, and so I stopped using that button. And then desoldered the button to eliminate it as a factor.

Seems it's not the button, it's the reset process on the board. The board is being set like the reset button is on, but never off, once it reaches that point.

Why would it do that?
 
Does this system use a 82284 clock chip? Since it handles the reset signal, maybe it would be a good place to start.
Sorry I can't be of more help; my last memories of Computerland were of the Millards and Werner Erhard.
 
I didn't find a chip of that number on the board. But I did a little basic investigating of my own, and seem to have fixed things in a way that disables the reset.

Of course, the answer I find so infuriating on any forum of any inquiry of an electrical problem is, "it's probably a bad capacitor." Not because that answer is wrong, but because it's practically useless. Anyone can give that answer. So - knowing the likely thing to fail is a capacitor, I traced the reset button to a capacitor, and removed it.

Played my first full game of PC Donkey Kong in a long time - before the fix, it always resets before I can get a game over. And screw that youtube video that calls the PC version of Donkey Kong the worst - you just have to know how to play it. Step 1, don't use a joystick.

Anyways - don't know if the capacitor I removed is bad, or if I just disabled something that makes another bad component no longer effect things. I suppose the next step if I wanted to fully restore things would be to try putting a new capacitor in place, and see what happens. But right now I'm just happy to have things working stable once again - to be honest, not having the reset button on the back of the PC working really isn't a big deal. Not like I used it all that often, usually if a reset is needed a ctrl-alt-delete does it. And if not, the big red on/off switch is closer to reach than the reset button. I don't think I ever pressed that button once on the family PC we had in my years of using it. So - it's a project for another time, that I might never get to, due to it being low priority.

What's of a higher priority is tracking down a set of binders and disks for the thing. Until then, I'll never know if my battery replacement was successful and allows the thing to hold onto the current date and time.
 
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Okay, I did a little research. If I'm understanding you correctly, you have the 8088 card installed and not the BC286 card. That actually makes things a bit easier. Can you post a nicely detailed photo of the CPU card? That will at least give us a starting point.
 
I will be sure to do that next time I have the thing opened (which I'm sure will be soon, I'm always tinkering, or putting in the XT-IDE card to transfer over more games to the HD). For now, the computer is "fixed", in that with a little more playing and testing, I can confirm the resets no longer occur without the capacitor I removed. Was able to play multiple games without any problems.

And yes, that is correct, it's a BC88 with the 8088 card installed.
 
On 2nd thought - doesn't take a whole lot of effort to get the card out and take some pics, and I certainly want to help expand knowledge of this unique machine, so of course I'll share pics when asked.

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Ah, that helps. Note the 8284 near the 24 MHz crystal at the bottom of the board. That controls the reset line. I suspect that your machine has a turbo mode as well, so what, 4.77MHz/8Mhz operation?
The oscillator for the 4.77 Mhz operation is the the 74LS04 adjacent to the 14.3818MHz crystal. Turbo switching is accomplished by input on the 8284 F/C pin 13. Reset is governed by an input to pin 11 (low=reset) and is conditioned and output to pin 10 (high=reset).
If the system resets in both the normal and turbo mode, I'd take a hard look at the circuitry around the 8284. First of all, make sure that you're not battling a cold solder joint--the pad around pin 18 looks a little dicey. The reset circuitry is triggered by the network of C12, C13, R7 and D4.
 
Wow, this is great information, thanks. You seem to understand these cards and chips quite well. Perhaps you can assist in identifying requirements for some features that currently aren't working without the ComputerLand version of DOS.

This computer has a battery, and should be able to hold onto the date and time - do you happen to see what chip or hardware is responsible for that? Perhaps there's an installer out there that will work with it?

Also, the computer has 2 LEDs on the front of it, a red one for HD operation, and one that would identify the speed, I believe it switches between amber and green to identify which mode it's in. Any idea what would make that work again?
 
U20 is the clock chip, a MC146818
Looking at the motherboard, my guess is that J4 is probably a battery connection and J5 might well be for a turbo LED.
Only seeing one side of the PCB, I can't say much about the turbo activation; however, it was not uncommon for turbo mode to be activated by a specific keystroke (e.g. Ctrl-Alt-keypad minus), but I can't say for certain without seeing the reverse side of the PCB.
 
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