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 faulty motherboard section...
Under closer inspection the board looks good, and I re-seated all the socketed chips save for the memory. The clock has the correct frequency, and it looks to have quite a bit of ringing to it:
However, no pulses on pin 13 of the 8253 chip, so on to the ground I/O CH RDY Procedure!
I have to stop here and say this whole troubleshooting section on www.minuszerodegrees.net is amazing and so well put together. It’s a great example to learn from and could be used as applied knowledge to other machines. Truly great stuff.
So I’ve verified that all of the things are true at the top of the I/O CH RDY Procedure: (I forgot to mention I burned a Ruud's diagnostic ROM onto a 2564, more about that at the very end)
• Motherboard proven as faulty; and
• Motherboard is not faulty in a way that overloads the power supply (see here); and
• No on-screen video; and
• No POST beeps from the IBM BIOS ROM; and
• You tried re-seating socketed chips; and
• A thorough visual examination of the motherboard did not reveal a problem; and
• No error beeps from the SuperSoft diagnostic ROM; and
• Use of a logic probe does not reveal pulses on pin 13 of the 8253 chip - see here. <---- Pulses would indicate that the IBM BIOS ROM (or SuperSoft ROM) is being executed
• You have verified that the 8284A chip is generating a 4.77 MHz clock signal, and you can observe that clock being received on pin 19 of the 8088 CPU, and observe it also being received on pin 2 of the 8288A bus controller chip.
• You have verified that the reset pin of the 8088 CPU is LOW.
p.s. I also verified all three voltages are present in each row of memory.
Everything up to step 9 of the procedure is good using the original 5700671 IBM ROM, but after that it gets muddy:
Occasionally I noticed that there would be beeping, but the beep is so quiet it can barely be heard unless you put your ear very close to the speaker. It’s inconsistent and I can’t get the beeps now, and I didn't have them consistently enough to cross-reference to the diagnostic rom manual. At one point there definitely was quiet two-tone beeping. Very hard to hear though.
I just noticed that the 8284A chip is very hot. Not fry an egg hot, but if you hold your finger there for more than a few seconds you can feel it start to burn.
I’m using TMS2564-35 eproms and they seem to erase, burn and verify fine on the GQ-4X using the 2564(TEST) profile.
Under closer inspection the board looks good, and I re-seated all the socketed chips save for the memory. The clock has the correct frequency, and it looks to have quite a bit of ringing to it:
However, no pulses on pin 13 of the 8253 chip, so on to the ground I/O CH RDY Procedure!
I have to stop here and say this whole troubleshooting section on www.minuszerodegrees.net is amazing and so well put together. It’s a great example to learn from and could be used as applied knowledge to other machines. Truly great stuff.
So I’ve verified that all of the things are true at the top of the I/O CH RDY Procedure: (I forgot to mention I burned a Ruud's diagnostic ROM onto a 2564, more about that at the very end)
• Motherboard proven as faulty; and
• Motherboard is not faulty in a way that overloads the power supply (see here); and
• No on-screen video; and
• No POST beeps from the IBM BIOS ROM; and
• You tried re-seating socketed chips; and
• A thorough visual examination of the motherboard did not reveal a problem; and
• No error beeps from the SuperSoft diagnostic ROM; and
• Use of a logic probe does not reveal pulses on pin 13 of the 8253 chip - see here. <---- Pulses would indicate that the IBM BIOS ROM (or SuperSoft ROM) is being executed
• You have verified that the 8284A chip is generating a 4.77 MHz clock signal, and you can observe that clock being received on pin 19 of the 8088 CPU, and observe it also being received on pin 2 of the 8288A bus controller chip.
• You have verified that the reset pin of the 8088 CPU is LOW.
p.s. I also verified all three voltages are present in each row of memory.
Everything up to step 9 of the procedure is good using the original 5700671 IBM ROM, but after that it gets muddy:
- During Procedure 10 of 13 (exercising the data buses all zeroes) I can burn all zeros to a 2564, but when I run the procedure I get all ones on the data bus (directly on the eprom, and at the cpu)
- Procedure 11 of 13 (exercising the data buses all ones) appears to work, but I don’t have confidence in it because the previous test also had all ones on the data bus.
- I haven’t attempted 12 or 13 yet.
Occasionally I noticed that there would be beeping, but the beep is so quiet it can barely be heard unless you put your ear very close to the speaker. It’s inconsistent and I can’t get the beeps now, and I didn't have them consistently enough to cross-reference to the diagnostic rom manual. At one point there definitely was quiet two-tone beeping. Very hard to hear though.
I just noticed that the 8284A chip is very hot. Not fry an egg hot, but if you hold your finger there for more than a few seconds you can feel it start to burn.
I’m using TMS2564-35 eproms and they seem to erase, burn and verify fine on the GQ-4X using the 2564(TEST) profile.