Amp now working but loud Hum.

Discussion in 'DIY' started by grabread, May 29, 2017.

  1. grabread

    grabread Active Member

    Messages:
    324
    Location:
    UK
    Thanks Pete. The power supply seems shorted to ground, is this normal if its a short on one of the boards?
     
  2. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    23,019
    Location:
    uk.. the middle bit
    supply to ground short if on secondary side of things could be many things . output devices are number 1 suspect . then the rectifiers .
    if on primary transformer is shot or wiring is shorted
     
  3. Binkman

    Binkman Addicted Member

    Messages:
    5,792
    Location:
    Raleigh, NC
    Pete is pretty sharp on the 220 UK transformer stuff, I'm at the 120vac in USA... wonder if elnaldo member.. could chime in. wonder if there is a thermistor in the transformer? here in USA a lot of transformers are center tapped to ground etc. just not that familiar but elnaldo comes across a lot of these situations.. hope it can help.
     
  4. grabread

    grabread Active Member

    Messages:
    324
    Location:
    UK
    Thanks Bink, Calling Elnado
     
  5. Binkman

    Binkman Addicted Member

    Messages:
    5,792
    Location:
    Raleigh, NC
    Just emailed him. pretty busy guy but checks it.
     
  6. elnaldo

    elnaldo Addicted Member

    Messages:
    6,428
    Location:
    Buenos Aires GMT-3
    Hello, I don't think I can do better than what you are already doing.

    What you posted first, (HUM) and your actual situation (shorted PS) makes me think in some rectifier or capacitor that started to fail (HUM) and finally gave up (short), but it could be HUNDREDS of things inside an amp.

    I'd start disconnecting the transformer secondary from the circuit (perhaps removing a fuse is enough) and start from scratch, checking with a Dim Bulb if AC voltage is OK and the transformer is working, then I'd check the diode bridges, then check you don't have a short between - and + rails to ground, all this passive checks before connecting the AC again.

    A link to the schematic or a crop of the PS section will help.
     
  7. grabread

    grabread Active Member

    Messages:
    324
    Location:
    UK

Share This Page