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H/K 930 Help!

M

mwetzel

New Member
I have a H/K 930 receiver and I have a problem. Occationally I hear a popping sound comming from the right speaker and the sound goes out and then comes back on in about 10 seconds. The first time it happened it blew the right speaker fuse and blew my Klipsch RB3 woofer in the right channel. I now have Boston Acoustics A70's hooked up and I am having the same problem except without my woofer blowing. My tech. can't or doesn't feel like finding the problem. He told me the unit is just to old. Can anyone help?
 
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If you decide you don't want to fool with that HK 930, you can sell it on ebay for good buckage.
Just please don't throw it away.

I'd find a better tech if I were you, he sounds like a modern supremecist. Truth be told, it will cost you several thousand dollars to replace the audio quality of that receiver.
Find a good tech who will fix her up.
You might contact echowars on this board.

Your problem sounds like output transistors. That shouldn't be a hard repair if you decide to do it yourself. www.mouser.com has any transistor you need. Please consult an expert first on this board however.
 
Sounds like a weak transistor on your right channel driver board, or you may simply have a cold solder joint. Driver transistor failures very commonly short full rail voltage right to the signal line (and into your speaker, as you've discovered). Your outputs are probably okay - for now, anyway. Do you notice this happening more when you first turn the unit on, or more after it's warmed up for a while? Does mechanical movement or vibration have any effect? How comfortable are you regarding "diving under the hood" on this unit?
 
The 930 is an awesome receiver! Find a way to get'r fixed. If you live in a metropolitan area there's got to be a tech in the book that specializes in vintage

Good luck!
 
The problem generally happens within the first 45 min after turning the receiver on. As far as movement it happens while we are sitting down. I am not a tech but I don't mind "diving under the hood"
 
Thanks for the reply. As far as the popping manifesting more when the unit is cool, that leads me to believe that the problem is more likely a connection issue, since heat tends to improve poor connections and mitigate symptoms.

I don't happen to have a service manual on this particular receiver, so I'm not sure how the boards are laid out inside. Can you shoot us a few pictures with the top off so I can identify the driver board location? (Anyone else - feel free to chime in here, if you know.)
 
Thanks for posting the service manual. Maybe someone can help with my problem by looking at manual. Thanks in advance.
 
Thanks emakay, you ROCK!!

mwetzel - start by popping the top and locating the driver board (it's called he "Predriver board" in the service manual). It appears to be mounted to the rear vertical surface. Find a non-metallic object (I use an old wooden dowel rod) and, with the receiver powered up and hooked up to a crummy pair of headphones, start tapping on the driver board in various places. See if you can get the popping to start based upon tapping or other mechanical manipulation of (flexing slightly, for example) various areas of the driver board. Be careful not to use your fingers if you're not used to working on electronic equipment - you could get a nasty "bite", or worse.

If mechanical tapping or other manipulation has no effect, run to Radio Shack and pick yourself up a can of "Component Cooler". Locate transistors TR625 and TR626 on the driver board (check pg. 11 on emakay's service manual for locations). Even a fleeting collector to emitter short in either of these parts will shunt + or - 39V directly to your right speaker. After the receiver has warmed up, give each of these transistors a SHORT burst of freeze spray. If you get an immediate pop, you know you've found the culprit. If not, continue up circuit and cool TR623 and TR624, then finally the differential pair TR621 and TR622. If you can't trigger the symptom by freezing these six transistors and mechanically manipulating the driver board, it's time to sew her up and take her to a pro. Good luck! :thmbsp:
 
BTW, I was looking through the service manual, and apparently, you have "MAIN AMP" and "PREAMP" jacks. Before you do anything else, remove the jumpers from these rear jacks and let me know if you still get the popping on warm up. If not, the problem may be in your preamp circuitry, rather than on the driver board (not likely, but possible...).
 
If removing the jumpers completely alleviates the symptoms, then the problem is in the preamp circuitry. That makes things a bit more complicated, since there are more components involved, and the preamp board will most likely be more difficult to get to. Try warming it up a few more times without the jumpers, just to be sure. I'll check the service manual tonight when I get home to see what's involved...
 
skibjr, when I turned off the receiver a pop sounded from the right speaker. I don't know if this means anything.
 
Well, the "pop" at power down indicates that you DO have DC on the right channel power amp signal line, so, my guess is that the trouble-making component acts up sometimes, but not others. In fact, it may have failed completely, leaving you with steady DC on the right channel. Do you by chance own a VOM (Volt-Ohmmeter)? Let me know...
 
skibjr said:
Thanks emakay, you ROCK!!

mwetzel - start by popping the top and locating the driver board (it's called he "Predriver board" in the service manual). It appears to be mounted to the rear vertical surface. Find a non-metallic object (I use an old wooden dowel rod) and, with the receiver powered up and hooked up to a crummy pair of headphones, start tapping on the driver board in various places. See if you can get the popping to start based upon tapping or other mechanical manipulation of (flexing slightly, for example) various areas of the driver board. ...
Click to expand...
That's precisely what I did to fix a similar problem in my HK670. It had a problem with intermittent popping/nasty static coming out of one channel. The above technique isolated the problem to the small vertical heatsink (on the main amp board) which holds the predriver transistors together. The problem was a cold solder joint. I refreshed the solder joints with a 25Watt iron (after attaching an aligator clip to the transistor leads to absorb excess heat). Has been working great ever since!
 
Okay, no prob. Based on the pop at shut down, I still think our trouble is on the driver board. The DC voltage on the signal line (causing the "pop" in your speaker) can't be coming from the preamp because you've taken it out of the circuit by disconnecting the jumpers. Knowing how much voltage is present, and its polarity would be helpful, but it's not absolutely necessary.

When you have some time, go ahead and perform the procedure I outlined in post #10 of this thread. With any luck, you'll be able to quickly narrow down the problem to a small area of the driver board, or even to a single component. Let us know how it goes... :thmbsp:
 
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