Vintage Ibm Pc (5150) - Speak Makes Buzzing Noise On Power On.

This is part of an ongoing issue which I thought was PSU related.

Brief background: I have two of these machines - A plain 'out of the box' one, and one which has been upgraded with a HDD card and an INTEL Inboard 386 card. I have managed to get the 'plain one working, and I have swopped the PSU's around, so I know that they both work.

The problem is with the upgraded one

At first nothing happen on power-on. The power fan came on, but there was no significant reading on the MOLEX plugs - only just 0.08V. Now when I power on all that happens is a constant buzzing from the speaker. This is not the POST beeps – I am not sure it is even getting to that point – it is just a constant buzz. I have tried removing all the peripherals, except the Inboard 386 chip. I have just disconnected the ribbon the board, which I have taken out, but left the other end connect to the motherboard, in the 8088 slot.

I would prefer not to dismount the motherboard if this can be avoided, but, apart from replacing the original 8088 processor, this is my next step.

Any comments/ guidance would be appreciated

 

My 5150 knowledge is just about all forgotten. I would check your VRM voltages are set correctly for the CPU you are trying to use. Sorry, that is about all I have. Will it boot with stock cpu?

 

Thanks for this. I have tried it with the original 8088 chip, and have also dismounted the whole PC, leaving just the PSU, the motherboard and the speaker. What is interesting is the the output to the speaker is not constnat - sometimes around 5V, and the it can drop to almost nothing. The speaker doesn't alway buzz - sometimes it starts very loud, and then drops off, sometime to nothing. The 8088 does show a noticeably increase in temperature to the touch.