Ohms level on power

[zfrenchy]

Just got an ATARI 1040 STE, before power up I re-capped all, then I am in phase of checking-up.

With only the motherboard, nothing connected on any port, not even power supply, between +5V and GND (pin 1 and 3 on power connector) I got 115 ohms (looks like a capacitor, start at 90 ohm then raise to 115), I cannot find any data on the Web about it, what should be "normal".

If anyone with a working 1040 STE can test and tell me if is same ?

NOTE: between 12v and GND it is open loop.

[rubber_jonnie]

I don't have an STE I can test easily, but an ST does a similar thing on the 5V input and clicks up to 158R. 12v settles at 15K but needs a while for the multimeter to get there so does read 0R for a moment.

Given there are many components involved, capacitors included, you are going to get some sort of reading, and looking at the schematic will help you understand to a degree, but unless you have a dead short, it's not going to really be a useful reading IMHO.

My personal preference is to hook up a bench PSU to the 5v input (12v is not needed to boot an ST/F/M or STE) and set the power level to something really low, so not enough to boot, and make sure there are no components that are getting warm. I slowly increase the power checking each time for evidence of overheating, and eventually take it to the power needed to boot. I usually set the overcurrent protection at about 3A @ 5v, which is the rated amperage for 5v on the ST type PSU.

For the PSU I use some of the resistors exxos has in the store to power on with a load and be sure the voltages are good before I plug it into the ST. Be aware that the load resistors do get pretty warm during testing if all is well.

[zfrenchy]

Agreed, schematic and all component involve is not easy to track any hard or soft shorts, I ordered a thermal camera and will do the power injector test.


Thanks for your reply. ;)