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  by Bill Degnan - 06/03/2014 12:16
Cromemco System 1 C5 1uF 50v cap replaced.
Board position C5 1uF 50v cap replaced (orange film for blue cylinder). No effect, 12 v line still 11.5-11.7v. System does not boot disk. Click image for larger view.

CS1 590uF 20v cap in position C1
It's too large for the space, but it's the right part for the job...a new cap in board position C1. Click image for larger view.

I removed the 590uF 20V cap from the 12v line of System 1 power supply and replaced. This was the solution. The voltage is still lower than 12v, but apparently it was not so much that the voltage was too low, but the 590uF cap was marginal.

I bought a Peak ESR70+ to test for bad caps. Seems to work very well.
Although the cap I removed was labeled 590uF / 20v, when I tested it I got 841uF and ESR - .13ohms. See readout

Am I correct to interpret this to mean:
1) They labeled the cap 590 but it was really a ~850uF to start with OR it deteriorated somehow to add MORE capacitance over time?
2) Assuming you have a new 850uF cap, an ESR of .13ohms is too high/marginally leaky
3) If it was really a 590uF an ESR = .13ohms would have been "more OK".

I posted this question to midatlanticretro so see what the experts there might think....

whatever, the new caps work.



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