MA5000VZ fans running fast
Posted 28 January 2013 - 11:08 AM
Ch2 also has a small fault, though i don't think its related. The soft-start precharge doesn't work. The amp powers up and when the soft-start time has run out the main relay comes in, dimming the lights and sometimes blowing the breaker because the capacitors are empty.
Posted 29 January 2013 - 04:40 AM
I've also sorted the fan issue, someone had cut the ODEP lines where they meet the control board.
However I still have the Ch2 in IOC protect. Measuring the +/- dc bus gives uneven readings..39V on one and 48V on the other. I've fitted a new ;'main' back card and that fixes it..so the fault's on there somewhere.
Posted 30 January 2013 - 08:48 AM
I believe I responded to a recent post for a similar symptom.
Posted 30 January 2013 - 03:03 PM
This was a difficult one. I discovered that the +ODEP voltage was perfect at 12.6V...however I spotted today that the voltage was positive with respect to 0V...it should be negative -12.6V !! So we had a hard odep fault on Ch1.
After 3 long days of testing, swapping chips, testing for leaky capacitors etc., I finally found the fault. The Thick Film resistor network RN101 had an out-of-tolerance section (pins 3-5). I found out by exchanging the network for the one in Ch2 and the fault transferred over.
I now just need to make & fit a new ribbon cable to replace the one damaged by a previous engineer.
Posted 01 February 2013 - 10:57 AM
Biggest fault on MA5Ks are the solder connections (base leads) of the output devices. Every few years they have to be inspected for cracks and such. Though, most of the repairs I've seen were related to ouput device faults. Also make sure that output devices are well 'thermal pasted', heatsink and device!
Posted 05 February 2013 - 03:43 PM
I agree, me neither. I was so glad to find it.
On your last point, I have spent today resoldering the output devices on 2 MA5000 amps. Brittle, crystallised solder and loose connections on the end transistors causing the pcb to become loose. Sometimes this causes the transistors to fail.
Posted 07 February 2013 - 08:50 AM
Posted 08 February 2013 - 01:48 PM
Posted 19 February 2013 - 03:30 PM
Posted 21 February 2014 - 05:10 PM
Posted 24 February 2014 - 10:58 AM
I'll keep your diagnostic in mind!