Hi all,
Wondering if somebody could guide me as to how best to proceed.
I have been asked to take a look at a graphics equaliser by a friend of mine. When he gave it to me it would not power up at all, but upon switching the mains power to off, a standby button would light up for a few seconds, indicating that there was definitely some power getting around inside.
So I opened it up last night and did some testing. My first suspicion was a capacitor gone faulty somewhere, but visual inspection showed no obvious problems. I then tested each one in circuit with an Atlas ESR meter and again nothing showed as a problem. I decided to reconnect everything to mains and start checking voltages to see if I could isolate the fault. Lo and behold it powered up perfectly ! However after several tests I find it will power up maybe 2 times out of 3. So it has now gone from not working at all, to exhibiting a sporadic fault. I have checked to see if there are any obvious solder issues that my proding around might have temporarily corrected but again I can't find any obvious issues. I'm a bit perplexed.
I did notice, while checking voltage on the high voltage capacitor (which appears to be good) that sometimes placing my probes on the cap would cause it to power off, or on, but I can't always recreate that anomaly.
The SMPS which is part of the main board appears to consist of a varsitor, some suppression capacitors, a choke coil, and an RU RS206 bridge rectifier. Voltage all seems fine on the high voltage capacitor.
This is as far as I have checked. It also has a TOP245YN Off Line Switcher which I don't know how to test properly.
The board is quite condensed with a mixture of through hole and surface mount components so the less I have to desolder in testing the better for fear of causing extra damage.
Is there anything obvious that I might be missing here ?
Any advice is appreciated.
Many thanks !