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Dagwood
March 4th, 2020, 01:11 PM
I've been tinkering with a dead Grid 1450sx for a while now. I recapped the power supply and am now getting my 5v, +12, -12, etc. but the computer still refuses to come to life. There are a few pins on the power supply to mainboard connection that haven't been able to ID yet. They either are logic signals or non functional power rails. The PSU provides separate 5v rails for memory vs. logic. Memory is getting 5v but logic is getting less than 1 volt. When the PSU isn't interfaced to the mainboard that 1v is 5v so I suspect it may be failing under load or there is a short on the mainboard that I haven't been able to find yet. Resistance from +5v to ground measures 35 ohms. I don't if that's appropriate or not, sounds low to me but I really have nothing to base that on. I tracked down the chipset's 'power good' pin and it's not getting a signal (no surprise).

If someone has a 1450sx that would be willing to crack it open and take a few measurements that would be great. I could let you know what I need.

Thanks.

Paralel
April 5th, 2020, 09:56 AM
How long are you giving it between measuring 5V to ground? Some times if you have a decoupling cap on the line, it can take several minutes for resistance to come up to infinite as the caps need to be charged first. I can tell you on circuits I have designed, when I have a decouple cap, +5V to ground will read about 40 ohms at the start, but after several minutes, it will read infinite once the voltage has stabilized and the caps are charged.