I fitted a socket for the LS156 and dropped one in, then added in the power transistor, popping on a bit of thermal paste to help it along. It should be a higher rated component than the original and be more capable.
With the new 723 VRMs in place, this nicely fixed the 12v and 5v circuits, so the machine could be powered up using its original PSU once more!!!
However, I was still getting garbage at boot up, but everything suggested that I had all the signals across the address bus and I was seeing data. I decided to pull my nasty 41256 RAM hack and see what happened, and got a screen full of @ characters instead!!
I checked all the 41256 RAM chips and found a bent pin on one of them (ARRRGHHH!!), so straightened it all and put them all back in taking extra care not to bend any more, and got this:
- PXL_20220906_210147531.jpg (147.08 KiB) Viewed 1599 times
I tried entering the MEM size of 16384, but it didn't like that, but I found after hitting enter a couple of times, it dropped me to the basic prompt, notably R/S (Radio Shack) Level 2 basic, so I wrote a little program:
- PXL_20220906_210250758.jpg (135 KiB) Viewed 1599 times
And it ran just fine
- PXL_20220906_210307269.jpg (170.79 KiB) Viewed 1599 times
I don't honestly think the RAM is quite right, as I don't think I should see the MEM SIZE prompt, but it is working, and the RAM has scope for improvement
Fingers crossed the last piece of the PSU puzzle, the Zener diode for the crowbar circuit, will arrive tomorrow, and though it runs fine without, the lack of protection is a worry.
What was also fantastic, is that my IDE based keyboard cable repair works perfectly, as does the whole keyboard, so I'm pretty happy at this point.
I think a 'Woo Hoo' is in order!!!
