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PostPosted: Tue May 16, 2017 1:06 pm 
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Joined: Thu May 04, 2017 1:03 pm
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Location: Toronto, ON, CA
I have an hk825 pre-amp that has channels cut out intermittently. I've had it repaired a couple of times but it comes back. Is this a typical problem with this amp? Is it something I should have a go at fixing myself or can someone recommend someone who can fix it permanently? You know.....within reason? It sucks paying to get it repaired only to have the problem come back in a few months. Been there, done that a couple of times.

Thanks, neil.


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PostPosted: Tue May 16, 2017 1:17 pm 
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Joined: Sun Mar 31, 2013 6:10 pm
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Location: Toronto, ON, CA
Welcome to Cam forum.
I would suggest either Tom McCartney in Toronto or Dan Santoni in Hamilton.
Both are great !

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PostPosted: Tue May 16, 2017 3:00 pm 
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Joined: Thu Aug 07, 2008 10:57 am
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Location: Montreal, QC, CA
I have the same preamp, it's great when it works. But these do develop problems over time, namely bad caps, bad solder joints and oxidized switches and relays. It takes more than a shot of Deoxit to bring these back I'm afraid. It's worth it though if you can bring it back. The all discreet design is great. Good luck!


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PostPosted: Tue May 16, 2017 11:13 pm 
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Location: Regina, SK, CA
My fallback fix to most aging equipment like this is the relay. It can fool you into thinking control cleaning, caps, but soon as it begins to falter, replacement corrects a lot of intermittent issues.
Amps most often come back to life after the protect is replaced.
I see a miniature relay on the power supply. Without further mapping of the circuit, this is potentially 'it'.
If you have a pencil iron, steady hands, you could spend a couple hours retouching connections on the major circuit board with little dissasembly. Just the top and bottom off will give you lots of access. For the little transistors, you should have a set of clamp on heat sinks to bleed off heat from the iron. Or if you are not feeling up to it all, do resisrors and cap connections, other connections with out chips etc and see if you get any improvement.
Check caps for bulge or leaks. A sure sign it needs cap work. Those are pretty simple on a board like that.
As it is intermittant signal failure, not noise, the transistors are likely ok. Phono section fuzzy noise is often a transistor.
Good luck.

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PostPosted: Wed May 17, 2017 4:55 am 
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Location: Toronto, ON, CA
Thanks Chipmunk1957, vincei and Sasklite for your responses. I'll try to get hold of Tom McCartney, but also thanks for shedding some light on what the problems most likely are.


Cheers, Neil.


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PostPosted: Thu Jun 01, 2017 6:17 am 
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Location: Toronto, ON, CA
I have gotten my hk 825 repaired and completely overhauled, and it is now working flawlessly. I called Tom McCartney first but he was out of town on a motorcycle trip. He got back to me on his return but I had already contacted Drago Fucec, who was highly recommended by my neighbor. Anyway, Drago recapped the unit and removed all the old glue which over time had become a conductor. I'm certain a very tedious job but all done in less than a couple of weeks from initial contact. So at this point, after having a good listen, I'm very pleased with the result!

Cheers, Neil.


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PostPosted: Thu Jun 01, 2017 7:17 am 
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Location: Markham, ON, CA
nimac wrote:
I have gotten my hk 825 repaired and completely overhauled, and it is now working flawlessly. I called Tom McCartney first but he was out of town on a motorcycle trip. He got back to me on his return but I had already contacted Drago Fucec, who was highly recommended by my neighbor. Anyway, Drago recapped the unit and removed all the old glue which over time had become a conductor. I'm certain a very tedious job but all done in less than a couple of weeks from initial contact. So at this point, after having a good listen, I'm very pleased with the result!

Cheers, Neil.



I can wholeheartedly recommend Drago. Not only technically sound but a nice, honest guy.
I am sure Santorini and McCartney are also sup0er guys; I have heard nothing but good things about them as well.
Best of luck!


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PostPosted: Thu Jun 01, 2017 1:51 pm 
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Location: Montreal, QC, CA
nimac wrote:
I have gotten my hk 825 repaired and completely overhauled, and it is now working flawlessly. I called Tom McCartney first but he was out of town on a motorcycle trip. He got back to me on his return but I had already contacted Drago Fucec, who was highly recommended by my neighbor. Anyway, Drago recapped the unit and removed all the old glue which over time had become a conductor. I'm certain a very tedious job but all done in less than a couple of weeks from initial contact. So at this point, after having a good listen, I'm very pleased with the result!

Cheers, Neil.


Cool, I redid mine as well, including taking the proprietary replays in the phono section apart to clean them. There was also a ton of suspect solder joints I redid too. All is well and sounds fantastic, a real sleeper. Enjoy!


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PostPosted: Thu Jun 01, 2017 5:55 pm 
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Location: Kingston, ON, CA
Alps tried to make a mini push button switch to replace the full size ones they used to make. That's the switches behind those small square buttons.

those switches are a total curse.

Eventually all will fail and each requires them to be taken apart and sanded clean of oxide. (2000 grit, etc)

copper contact leaves sliding over silver plated contacts. the two dissimilar metals end up having an oxide issue.

the smallness of the switch and the difficulty of taking them apart -is the curse part.

I've got a HK 665i here (dual mono integrated, 100 wpc) that I bought off kijiji for $50, and that's what it needs. Besides all the signal level caps and regulated power supply needing to be being re-done. The unit is mint other than those over arching issues.

However. Not all of those tiny square buttons have the exceedingly failure prone mini alps switches behind them.

For example, the 825 preamp..does not. Here's the interior shot of the unit.

Image

The PM 665i and vxi units...DO have the hated mini switches.



If one has the patience to deal with those switches, they (all the HK amps and such from that series) can last many years again afterward, with no other issues.
The point is that all of those switches eventually need to be cleaned. And a proper cleaning is all about taking them apart. Which is what I've done many a time. Most people won't do it, it's too expensive, or time consuming. Off the scale time consuming. they generally just spray the switch with some given stuff they chose -and be done with it. Which is why the problems come back.

the problem with those small switches, is they can't be sprayed. too small, and it is difficult to get the given spray to move into the switch ---and do any actual cleaning of contacts. Just so it can be good for a while. The tear down is the only real cure.

Looking at the interior of the HK 825 preamp, if upgraded in parts quality....in today's money....that's $2500, at a minimum. So it's a keeper and a fixer upper. You can just see the alps 'black velvet' film potentiometer. Not the best pot in the world but better than the ~$75 pots of today.

Then the completely discrete and well implemented/organized phono section. All the important switches at the back with short signal paths and long shafts, as it should always be. This thing was built around the cult and ideals of SOUND QUALITY.

We used to have it so good.

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PostPosted: Fri Jun 02, 2017 7:05 am 
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Location: Coquitlam, BC, CA
I can concur that the switch contacts have to be physically cleaned to do it properly. Those tactile switches (behind the buttons) can be disassembled; sometimes the discs that pop back and forth need to be reformed. Of course new replacement switches would be better but there's another trick- swap seldom-used switches with the iffy ones and it's just a matter of soldering.


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PostPosted: Sun Jun 04, 2017 6:22 am 
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Location: Toronto, ON, CA
Interesting stuff......thanks for your insight. I have several pieces of interesting old equipment that is getting to that age where they need repair. No doubt that compared with the new junk, it's worth repairing the old stuff. Looks better, sounds better and weighs more!

Cheers, Neil.


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