Harman Kardon 930 troubleshooting

John in Canada
John in Canada Posts: 6
edited August 2006 in Troubleshooting
After reading other reviews on 1970's vintage HK's, I agree. I have had an HK 930 amp/rcvr for 30+ years and it is EXCELLENT! However, recently it has blown it's fuse instantly.

I have replaced the FOUR power transistors on the heatsinks. I have also replaced the FOUR 6800mfd (50VDC) power filter caps with 10,000mfd (63VDC). Still blows the 3AMP main fuse.

This happens with NO spkrs connected, volume all the way down.

If anyone has had any experience troubleshooting HK930, I would love to hear from you.

I have the Technical Manual PDF ( from HK themselves ) which shows the schematic and physical parts placement, but I wonder if there is a Troubleshooting Service Manual out there.

Thanx. John in Canada
Post edited by John in Canada on
· Share on FacebookShare on Twitter

Comments

  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited August 2006
    Hello John,
    Thanks for posting on the Forum. The way I try and trouble shoot a piece of electronics is to first isolate the power supply from all of the sections of the device that it is connected to. In a receiver there are, probably, power supply connections to the tuner, pre-amp and power supply sections. Usually they will have separate wires going from the power supply to these individual circuits. If so, then disconnect these wires, making a drawing of what color wire goes where. Now the power supply is isolated from the loads. Instead of a fuse in the main AC line substitute an AC current meter and connect the receiver to a Variac (hopefully you'll have one of these). So you'll be able to slowly increase the incoming AC Voltage and watch what is happening with the current. There shouldn't be too much of a current flow as the AC Voltage is slowly increased. If you can reach a full 110 Volts with less than .5 Ampere flowing through the meter the power supply should be fine. Then you can check what the Voltages are that are supposed to go to the various sections of the receiver. Look on the schematic and note what the DC supply Voltages are supposed to be and see if this is close to what you're seeing. You might want to measure the DC resistance of each of the sections of the receiver, the tuner, pre-amp and output stage. Try and look at the schematic for each of these sections and determine what it should be. For example if the tuner section has a resistor in series with the incoming power supply Voltage, see if the readings you get for that corresponding connection seem in line with what you would expect. Be suspicious of a reading that shows 0 Ohms. That would indicate that when the power supply is reconnected it would be developing a Voltage across a short. Not a good sign.
    I hope this is helpful information.
    Regards, Ken
    · Share on FacebookShare on Twitter
  • John in Canada
    John in Canada Posts: 6
    edited August 2006
    Hi Ken, thanx for your help. I was looking for a 'quick' fix. I figured after 30+ years, I might have a shorted power transistor or shorted filter capacitor. I will take your suggestion and isolate the power supply ( maybe it is one of the full-wave bridge rectifiers ) and see if the fuse blows. Then I will measure resistances on individual sections and connect them one by one. Wish me luck. John in Canada
    · Share on FacebookShare on Twitter