ampeg svt cl LEDs are down

Discussion in 'Amps and Cabs [BG]' started by cood, Feb 19, 2014.

  1. cood


    Jan 4, 2013
    Warsaw, Poland
    i have ampeg svt cl (1997 SLM made). the problem is LEDs (power and bias) are random shutting down. amp is still working and LEDs are down. after reboot LEDs are working some minuts and again going off.

    can anyone know where i can find solution of this problem?


  2. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Since all the LEDs are out, I would check is the + and - 15VDC power supply that powers the LEDs. Look for + and - 15VDC at the LED (R68, R70, R77, R79). There is a jumper J19 that you should reseat to ensure that there is a good contact and power is getting to the low voltage power supply. Then trace forward through the power supply to the LEDs.

    Since all the LEDs are out, they are probably ok but they need to be checked. This can be done with a small battery and a limiting resistor. The LED will work or it won't.

    The next step would be to examine the circuit that drives the LEDs. This gets more complicated.


  3. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Adam, being the safety freak that I am, I would advise not to open the amp unless you have much experience in working with 700V electronics, that's a lethal level. If you do have the required skills then do as BOT suggests. If not it's tech time.
  4. Hi.

    A HUGE +1 for Paul's post.

    Be safe.

  5. tjconn


    Feb 24, 2014
    I have a similar issue. But it is only one of the LED bias lights that won't turn green. Any thoughts?
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If the bias LED's work but one of them won't go green it could be an indication that your power tubes (or one or more) need to be replaced. If a tube can't be biased to the proper level, it is not working up to spec.

    Otherwise, the same advice as above applies. The LED could need to be replaced or there is an issue with the bias circuit.
  7. cood


    Jan 4, 2013
    Warsaw, Poland
    can you tell me how i can do it?


  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    It isn't something that can be described in this forum.

    The LED's are connected to either + or - 15 V through a resistor. They are turned on and off by a circuit that contains TL072 operational amplifiers. It is possible that there is something under the circuit board that is causing a short in the circuit. The first step would be to examine both sides of the board carefully for anything out of place. Next the circuit would need to be examined with test equipment to trace how it is working. Something a tech could do with an oscilloscope.

    The LED's can be tested with a 9volt battery connected through a limiting resistor (220 ohms would work). Like is shown here. Either the LED's will work or they won't. This can help if an LED is burnt out or shorted.