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All back together and working. Hey the 5160 has company now!

Thanks for that, once I get it all back together I'm going to look and see what diagnostic software can test these things. Maybe Check-It and InfoSpotter? A few extra notes: The memory expansion card was shorting out the power supply. Replacing two tantalum caps on the board remediated that...

Good stuff, I'll have to take advantage of those ports! I have the motherboard fitted back in the chassis, tested the Chauffeur and it's working. Starting to piece things together.

Cool, I hadn't seen that page before! Here are the cards that came with the machine. Frankly I'm not sure which is the display card! (for troubleshooting I've been using the video card from a 5160) IBM 64KB Memory Expansion Option STB “The Chauffeur” Multifunction Card?? IBM 5.25"...

I haven't hooked up a floppy drive yet Oh, good to know! I swapped bit 6 chip & 7 in bank 2 and confirmed that memory chip is bad because now parity error is 0880 after the swap. Luckily I have a few extra 4116 RAM chips here from a TI-99/4A VRAM fix ;) Popped one in, and we're back in...

The 8253 came today so I installed it, looks like we're a lot further, time so start hooking more stuff up, and thanks for your help with this!! (speaker is beeping now too) I've put the Cassette BASIC ROMS back in, but checks are still failing. I also put the original BIOS ROM back in the...

This trace is very impressive! I'm using an inexpensive ($12) 8-Channel USB logic analyzer with PulseView which isn't bad for free. I've applied a few decodes, but nothing this helpful! So at the moment I'm thinking how to do this trace in two steps, I'll have to see if PulseView has address...

Good strategy and thanks for sharing, makes sense. I'm still relatively new to this type of thing, and hearing other people's perspective is helpful. It's easy to get lost going down a rabbit hole, or the opposite, swapping chips without knowing what's going on. As usual the answer is...

Roughly looking into Ruuds DiagRomV2.asm I can see the routine is reading, writing and then comparing bits interfaced to the 8253. I'm also having a look at the 8253 datasheet. At this time I can't quite grok if the 8253 is failing, or something else is stomping on the bus. I'm not very...

Broke out the logic analyzer for this one. Here's what the overall activity looks like from boot to halt: Here's a magnified view of what the pulses look like in the middle:

Ok yes, confirmed 1.193 clock on pins 9, 15 & 18 of the 8253:

Ok finally have something! Still no beeps, but something on the screen!

Indeed that could explain it! (damaged chips) and I have been thinking what else could be wrong with them, although they seem fine on a breadboard. I created the diagnostic ROM and tried with the jumper, but alas still no beeps. I wrote all hex 55's on a chip as in step 12 of the ground I/O CH...

Results from the breadboarding session are in. I wrote hex 55 to one of these 2564's and did some testing. 0101 data didn't come out until I applied 5V to pin 28, so I'll create a small jumper wire, burn the diagnostic ROM and try again!

Can you post some example URL's / Posts please?

@channelmaniac yea I know right! I wouldn't have thought to do it, but minuszerodegrees.net has an article on how! Would have never thought of that myself :)

In the scope trace I posted, yes. At first it wasn't but when I saw the ringing I moved it to the ground of the 8284. There was a little improvement but not much. Yes, and now I can't seem to get any of the quiet beeping again. Thanks for checking that! Unfortunately I don't have a spare...

Hello, recently acquired a 5150 in good condition, however no signs of life. I followed the excellent troubleshooting guide at minuszerodegrees.net and ascertained there was a short on the 12V bus, after which I replaced the capacitors to resolve that issue. Still no beeps though, so on to the...

Just to close this thread out, I took the power supply apart again, de-soldered the vertical sub-board and cleaned up solder on the recap job. It looked fine, but afterwards the problem is fixed. There may have been a short to ground on one leg of one of the caps.

Something like this? https://ftp.whtech.com/hexbus_cc40_ti74/ti-74/