Help a newbie out with a busted up receiver - HK AVR 335

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Hi all!

First off, I'd like to state that my degree is NOT electrical engineering, and you guys are on a whole new level of knowledge on this site. That being said however, I'm tired of wasting time at sites who's only advice is too blow it out with air, "jiggle the handle", or take it in to a service center. I do like to play around with stuff, and one of my personally mottos is: "you can't learn anything if youre not screwing something up!"

I've been in the repair process for this for sometime now and my patience is purely coming to an end.

I have all the channels up and running now, except the front left is "crackling" badly and offers no headroom. All other channels are crisp and clean.

What would cause this and how would I go about fixing it? If you need to know certain voltages, I'll be happy throw it back together and test anything.

Thanks in advance for the help,

The first thing you need to do is locate the source of the distortion; I would start at the amplifier input and move backwards.
I am not familiar with HK internals, so this may be difficult to do w/o a service manual if the amplifier board is integrated with other components into a larger main board. On the other hand, if everything is largely separated and connector pins labeled, this may be easy.
Of course, this being said assuming you've visually inspected everything for any burned/broken components.
Info on repair work already completed would be helpful also.
chances are pretty good that the "crackling" is caused by an intermittent connection due to a bad solder joint. See if you can isolate it to one section of the receiver - tuner, pre-amp, power amp, etc. For example if it happens with different input sources the problem is after the input selector. If you can disconnect the pre-amp out from the power-amp in and drive the power amp with an external source, then you can isolate to pre-amp or power amp.

Then reflow all of the solder joints in that section, applying flux and fresh solder as needed. The service manual with schematics and pcb diagrams is a big help to understand what's what.

Thanks for your input and willingness to help. Since my last post, I have gone through and double checked some solder joints. After heating a few up, everything is working just fine on the amp board. Now that that is up an running, I have run into a new issue.

The DSP/input board has run into some problems. At times when I try to use any 2-ch to surround DSP, (i.e. Logic 7 or PLII) the audio will shut off on all channels. I traced it and the audio never appears to leave the input board. Sometimes it will run for hours straight no problems, while other times it will stop working after 10 minutes. Or work fine until I put the unit in standby and then a short time later power it up. The quick work around is to put it in 2 channel mode, which seems to work without issue. More importantly, the digital inputs do not work. Sometimes it will work fine for a few minutes, then "search" for a signal, and other times I will get a loud squeal or a hiss out of all 5 speakers.

Is this board screwed? Or is there a capacitor or other simple component that is failing? Again, I appreciate everyone's help and input.


If nothing else, this is a bump. I'm a semi-newb in need of some help.

I have found that the DSP board has a ribbon cable going to the video board with the markings of DSPCLK, DSPDATA, +15V and -15V. The voltage on DSPCLK is +2.875, and the more troubling one is the +15V voltage is actually +10.3 and the -15V voltage is -11.1.

Could this be the cause of none of the DSP functions working correctly? I have the service manual, but being a mechanical engineer (yes, one of those) it's all jibberish to me.

I've nursed this thing back to a working state (analog including 6ch direct work flawlessly and sound great). Now I just need to get the DSP/input board to get an analog signal to the amp board.

Any help is appreciated!

Just for good measure, try measuring the +/- voltages directly at the regulators. It's very likely that this receiver uses fixed 7815/7915 voltage regulators (they will be labeled as such); they will be located near the large supply caps used for the amp and may be mounted on small heatsinks. Also, make sure you're using the correct ground reference for voltages; the chassis may be isolated, though this is highly unlikely.
To really debug this you need the schematic, the ability to read it, and an oscilloscope.

The DSPCLK signal is likely clock signal, i.e. oscillating at a frequency of 10s of MHz or perhaps 100s of MHz depending on the vintage of the piece of equipment. Measuring it with a DMM won't give you meaningful results.

The +/- 15V lines might or might not be an issue. Likely they're used for the analog part of the board, and there's probably some second stage regulation to power the digital logic. Could be a linear regulator or switcher, again depending on the vintage, and might or might not be a problem depending on the type of regulator and the load it puts on the supply. This is all speculation.

See if you can get any of your EE friends to spend some time looking at it in exchange for suitable food and beverage. I used to work for beer and pizza, now it takes a really good steak, excellent wine, and single malt scotch afterwards.
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