Help with the repair of an IBM 5150 Personal Computer

[teddy06550]

Hey all i recently bought a 1985 ibm 5150 that would not POST at all with the hopes of repairing it and getting it working with no luck so far. I have checked that the power suply is providing all the correct voltages and it is but still nothing, have tried piggybacking ram to see if that helps but nothing and wondering if anyone knows what to check on these older computers (the caps are fine as the test for these is to see if the power suply overloads which it does not) i do hear a crackling on the speaker

Thanks
Ed

[james_s]

The first thing I'd check with any computer of this era after the power supply is the CPU clock generator and reset line. While not a PC, I've fixed a few Gottlieb arcade game boards that are 8088 based and more than once I've found a bad octal bus transceiver, the 8088 has a multiplexed address/data bus so if the chips that handle this are bad, not much will happen. If that all looks good, you might have bad RAM or a bad BIOS ROM.

[teddy06550]

Hi James_s
how would i test clock generator and reset line without an oscilloscope as i dont have one
Ed

[james_s]

Well you could use a logic probe, or in a pinch a DMM may be of some use. You will need some sort of test equipment though, with nothing you are flying blind and just guessing.

[orbanp]

Hi Ed,

Here is a link to the hardware reference manual, that should get you going:
https://www.manualslib.com/download/819833/Ibm-5150.html

Good luck, Peter