a5002 high side bias on channel 1Bias problem
Posted 06 June 2013 - 04:55 PM
Posted 11 June 2013 - 07:30 AM
If so, I can suggest that you 'wash' thoroughly the boards and refurbish the output and intra-heatsink devices (bias and sensor).
A good way of removing the excess water is via an air compressor. Or, bake at 125°F.
It is possible you may have stray electrical interference caused by board contaminants.
Of course, verify continuity of devices and components!
Posted 11 June 2013 - 04:32 PM
Posted 13 June 2013 - 07:36 AM
I do remember a few odd faults similar to yours: there are some (very) high voltage caps, brown in color, 400 or 500V tolerance, that in circuit may appear normal, has high resistance, because in parallel to other components. When removed, the caps were resistive!
Ah! now to determine if the fault is on the output module or main board: Just swap cards with the other side! Since you have a good side, swap modules until you determine where the fault lies. Then it is just a matter of time and experience to locate the defective component.
As for output devices, I rarely have intermittent faults; If a transistor is dead, then it will be dead. Though, I rarely had to replace drivers or bias transistors even when a major fault occurs on the outputs. If replacing outputs try to replace all the transistors that are located on the same base trace. Try to use graded devices or you 500x will return!
Posted 14 June 2013 - 10:03 PM
It turned out to be an intermittent high side bias 500 ohm pot that my new apprentice missed. It would sometimes test good when a little pressure is applied to it from the test leads. D517 and 516 were also defective.
Thanks for your reply.