First post, by FAMICOMASTER
- Rank
- Member
Now that my AT clone is working... Enough, I feel it's time to move on to my other project:
My Turbo XT clone.
It's a DTK Turbo 640 motherboard
Manual: http://minuszerodegrees.net/manuals/Turbo-XT% … ion%20Guide.pdf
TH99: https://th99.infania.net/m/C-D/30501.htm
It was originally in a case labelled "Turbo Beltron," but I swapped it into an other case, which says "PC Craft." Both cases have almost identical metalwork, the same power supply, the same diskette drives, and both cases had identical motherboards. The board that was originally in the PC Craft case had a clock battery explode on top of it and ruined the motherboard, it shows no signs of life at all. The only difference between the two cases is purely cosmetic, the PC Craft has no rust and the front plastic is designed more to look like an XT than an AT like the Beltron case. Otherwise they are identical.
When I bought the Beltron initially, the machine *seemed* to "work"
That is to say, I plugged it in, flipped the switch, the power light came on, and it made a POST beep. A single beep and it went silent except for the fan. Nothing out of the ordinary. I didn't have any sort of MDA/RGBI monitors to use with it, and I didn't have an 8-bit friendly VGA card either, so it sat under my desk for about a month.
I pulled it out recently since I finally got a working MDA monitor (A lovely little 12" Samsung green screen monitor I got for a very good price). The Beltron case looked awful, so while I was waiting for the monitor to arrive in the mail, I pulled the board out and stuck it into the other case. I also took the better of the two power supplies with it.
A while back, I'd pulled the first two banks of RAM (18x41256 DRAMs) to install in my AST Advantage for the AT clone. I pulled the bank back out of the AST Advantage and installed it back in the motherboard in the same two banks. I didn't touch the second two banks of RAM (18x4164 DRAMs). During this, I reseated the BIOS (the socket looked a little worse for wear) and installed an 8087-2 coprocessor. Used the manual to set the switches and put the board in the case, installed the generic I/O card it came with (https://th99.infania.net/i/C-D/52639.htm), which I set up to the best of my abilities... It is missing the two large jumper blocks across the bottom though, which are also unlabelled. FCC ID says it was made by Yangtech in Taiwan, but I have nothing else on it. Put a Video7 VEGA card in with it (https://th99.infania.net/v/U-Z/52394.htm), setting the switches for a monochrome monitor.
Flip the switch and... Keyboard lights flash and then one long beep. The beep never ends. Ever. It is at a constant tone and starts immediately after the keyboard lights flash, and nothing happens. Nothing on screen, no beep codes, just one tone until you hit reset or shut the machine off.
I've reseated all of the RAM chips (They all tested good in my AST, but just to be sure I swapped bank 0 and 1 with each other and still got the same results), I reseated the BIOS EPROM, and I completely removed the diskette drive controller and the 8087-2.
It's now an NEC V20, 640K, and a video card. There is nothing else installed.
It seemed to be working fine not long ago, what could have happened? How can I fix this? If I can just get it to put something on the screen I'll be content with it for now, even if it won't boot or something.
P.S. In this picture, it is the machine on the right. The machine on the left with no cover is my Turbo AT. The monitor is sitting on top of this Turbo XT.
The current setup on the bench:
