IBM 5160 Mainboard issue - C2, C7, C9, C58 bad - unreadable labels

[DoomWarrior]

Hi everybody,

I have the common issue with my 5160 mainboard. The fan of the power supply isn't turning when board is connected to the PSU. Without the power supply works fine.

I measured all capacitor and have bad readings for
C2, C7, C7 and C58.

C58 should be 10µF 16V
but have issues reading the values of the others.
C2 & C9 - "47µ" or "47p" and 2. Line "M C X [unreadable marking]" - could by 47µF but unknown voltage. The unreadable marking could be a "+" sign.
C7 - "47 [unreadable marking] M" and 2. Line "GGC (2)" or "CGC (2)" - could be also a 47µF

Has anybody information on which capacitor those are? Because all of them are shorten I'm also not sure what pin the + and the - pin is. Any suggestions are welcome.

Best Regards
D

 

[modem7]

Because all of them are shorten ...

Welcome to these forums.

When you do an in-circuit measurement of a capacitor that sits on a voltage rail, you are measuring not only the capacitor, but also all of the other components that sit on the voltage rail (i.e. a combined reading). To measure such a capacitor, you would need to temporarily take it out-of-circuit. For measurement, either completely remove it from the motherboard, or use a technique such as cutting one leg about half way up, than after measurement, solder the halves of the leg back together.

However, having just written that, there is an easier way in your case. Use the diagnostic procedure at [here], a procedure written specifically for the situation you are in. Based on the history at [here], that procedure may have you removing either C56 and/or C58.

 

[chris_nh]

http://minuszerodegrees.net/manuals/IBM_5155_5160_Technical_Reference_6280089_MAR86.pdf

The logic diagrams for the board show the capacitor values and what they are connected to.

C2, C7 & C9 are connected to keyboard lines and ground. Probably not bad, you may just be seeing a false short due to other components in-circuit. (see diagram sheet 9, pg. 1-43)

C58 is on the -12V rail, and this is a common one to fail. C57 is also on the -12v rail, so a short on either one of those caps would probably appear elsewhere on the circuit, like at the other cap for example. Try removing one or both of those caps to see if the short is fixed. (see diagram sheet 10, pg. 1-44)