HK930 with no output

[FickleBJT]

Hey everyone,

I have an HK930 that has been having some problems over the past several months. Up until today, the left channel would intermittently cut out, so I looked into repairing it myself. I replaced the power supply caps as well as the electrolytics on the preamp board, but that ultimately didn't help (I can replace the power amp caps but it would be a LOT of work...lots of wires to desolder). After that I tried cleaning the contacts on all of the switches (I had read that the tape monitor switches in particular can cause output problems), but that didn't help either.

Then today both channels cut out within a minute of each other and powering down the amp for a while didn't fix the problem. I've checked the fuses and they're fine.

Does anyone have any suggestions? I have a feeling that an oscilloscope would be useful here, but I don't have one at home.

[Tekko]

Prolly the output transistors blew, intermittence could have been critical solder joints opening up that eventually sent the amp into self destruct mode.

[FickleBJT]

In other words I should open up the amp and check solder joints throughout the preamp and power amp stages along with replacing the power transistors (after checking them of course)?

[djk]

If you lost the outputs you would blow some fuses.

Get the manual and trace the signal with an oscilloscope.

[jimmytwos]

i had one of these amps, really nice. i would check the speaker relays on both output boards and the fuses before suspecting blown outputs. these amps are quite tough and will play into a dead short at mid volume before going into 'protect' even then a power off/on will resume normal service. irrc- there are fuses on the amp boards on both sides. also give the relays a tap to see if they kick in? mine had rather nasty relays and would sometimes take a while to click on

[FickleBJT]

I have now checked the power transistors and they are all fine. Additionally, all of the solder connections are fine.

An interesting note is that engaging the speakers (with the physical spkr-1 switch) causes a small blip to be played out of the speakers, meaning that the amp section is probably working fine. It seems that the problem is the signal being lost.

Does that make sense?

[Tekko]

Sounds like a faulty speaker output selector switch.

[FickleBJT]

I guess I should have explained better. The 'blip' that I spoke of is something that has always been there; just a bit of static from the bounce of the switch. At no point does the sound being sent to the amplifier get to the speakers.

[mrfeedback]

Hi. Look for yellow contact glue on the pcb's that has gone brown/black....this is conductive and corrosive.
I recently repaired a HK 630 that was suffering DC offset in both channels because of conductive contact glue.
Excess dc offset will cause non operation of the output relays.

Eric.

[sregor]

? no relays in 930! Both channels dying suggest power supply / voltage regulator issues - perhaps from recapping? Do you have another amplifier or receiver you can run through the preamp out and pre in jacks - determine whether problem is preamp or amp (sounds like amp section is working, but I'm no there to test it ...) Good luck with it.