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help with Harmon Kardon PA 655 Vxi .. Posible chanel down !

C.A.P

C.A.P

Well-Known Member
help with Harman Kardon PM 655 Vxi .. Posible chanel down !

I just acquired a HK PM 655 Vxi and I went through the general cleaning of the pots.. however here is whats going on... One Chanel plays fine with full volume and the balance control works.. The other is way down almost inaudible with static on the volume and NO balance at all.. I am not sure I am picking up the other channel or what is going on,,, I have de oxit every switch twice and its done nothing.. to that side,, Its the same with a tuner and a cd player as well as both right speakers A and B Right !

There is no audible click at start up it just pauses 10 seconds then turns on with no relay sound inside the unit.. Could one Chanel be blown and still produce faint music ?? The volume pot get real static at near full volume but there is little sound with NO balance..

The one channel is really nice sounding.. I have read that these need cleaning alot but I am lost... Any ideas and if so whats the plan to get it back up ...

Also whats the story on this integrated unit? Will it run Vandersteens2c or am I better off with my Sony Str GX10es

I like the unis simplicity .. I also got a TD302 as well as the Tu911





Thanks for any help !:scratch2:
 
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These are good sounding amps that will run the Vandersteens and sound good doing it.
Harman Kardon used some horrible pushbutton switches in these- you can clean the hell out of them and use De-oxit Gold and they'll act up again a week later. Try pushing the switches in a little bit and wiggling them around to see if you can get the channel to come back- it'll help you figure out which switch it is. You might have to remove, dis-assemble and clean the switch contacts to get it working.
 
Ths364 said:
These are good sounding amps that will run the Vandersteens and sound good doing it.
Harman Kardon used some horrible pushbutton switches in these- you can clean the hell out of them and use De-oxit Gold and they'll act up again a week later. Try pushing the switches in a little bit and wiggling them around to see if you can get the channel to come back- it'll help you figure out which switch it is. You might have to remove, dis-assemble and clean the switch contacts to get it working.
Click to expand...

I read they are real famous for switch issues but sound wonderful when working.. I swear I have used a half a can trying to clean it.. IS there a way to know for sure if a channel is down.. Meter test? Why does the volume work fine on one side and its static on the down side..

Ill re clean and retest today as maybe it was wet from cleaning ...

I would like to test it against the Sony Gx10es
 
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How about some HK help fellas !

You have to be kidding me! There are no HK gurus here ? I know there has to be a secret password !

In all seriousness.. I re cleaned to make sure but same deal.. I have searched high and low and a few talk about adjusting DC off set , How would it go from working to not without something in the path going bad??

A few talk about the transistors q443 IIRC and its readings.. The good news is you do not have to tear anything apart to work on the boards as they are easily accessible 1
 
Just to make sure you did clean ALL the switches: the ones everyone here is talking about are the small square switches in the upper section of the front panel. These should be flushed several times and worked till your fingers hurt. The reason people say it's probably the switches is that they are a bugger to get to and many people either skip cleaning them and do the selectors only, or fail to clean them properly. And these switches do cause the symptom you described. Also make sure you clean the 4/8 ohm selector on the rear panel.

Other than that, sure, check the currents, that never hurts.

One quick test: have you tried setting the pre/main switch (front panel) to 'separate' and connecting the corresponding connectors on the rear panel with an IC cable? If not, try.
 
Hello my fellow polish brethren from Warsaw ! You are right! The top switches are tough to get at and I will be on them to-nite.. I know the loudness one has a hard thump when depressed.. I dont even know if its worth spending $ on to fix..
 
Judging by the reviews of the 655 and the sound I get from my 6550 and my 725, it is certainly worth the effort, $... well depends how much :) I did pay to get my Harmans fixed (both suffered from more than just oxidized contacts) and it was certainly worth it, but I bought them as non-working=cheap, and my tech is obscenely cheap. I'd lend him, but I understand you're in Detroit now, not Warsaw?

Anyway get to the top switches, flush them and see what happens. Google the harman 655 images, there are some repair photos. They will give you an idea how much you have to take it apart to get to the small switches.
 
PM 655 on my part and it runs Boston A-400 ( 4 ohms ) with ease.

Lookout thougt... no relay protection on these, that's why you do not here a click. It's a '' 10 seconds to get sound ''..... soft start.

But what bass extension do I get with this bad boy... very nice pairing with Bostons...
 
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The main culprit on these amps is the Pre-out / Main-in switch. It's hard to get the Deoxit in there but ya gotta do it. Other possibles are the speaker selection switch and the cartridge switch (if it's only phono). Both of these are located at the back of the chassis at the end of a long shaft or cable.
 
Im at ends with it.. Ill saturate the some bitch.. I ts frustrating .. I have 30 years in a trade and know it well and have been into audio for 30+ but its sad I have no real ability to work or diagnose circuits...

De ox or sledge hammer .. they both put a smile on your face when they are used properly !
 
Have you tried with pre out/main in bridged with an IC and the switch at separate?

In any case, the pre out/main in switch is the last point before the power amp. Find the wire that runs from this switch, feed the signal there to this wire (attenuated signal, for example from a headphone output of an mp3 player, start with zero volume and increase slowly). This way you can at least test if the power amp section is OK. More or less, speaker and impedance selectors are further downstream. This is what I did with my H/K amp.
 
OK I hooked up my CD player to the amp direct as I have a volume pot on it.. I switched the intergrated off and ran the cd player directly to the amp and BOTH channels work.. It has to be in the front end on the Pre amp section.. I took the volume pot apart and de ox it and it is clean no static but still one down.. It better news as the big money is in the amp section.. I will continue
 
That's good, you've eliminated half of the amp as a suspect :)

Do you have the service manual for this Harman? You could look at the block diagram and try going back block by block through the preamp feeding low level signal, see where the signal disappears in the problematic channel (best to use cheap headphones for such experiment). If the small switches are OK I would bet on tone control circuits, but you never know, best go step by step. Or you can take the signal from the volume pot out and feed it directly to the amp, if you get both channels this will further limit the search field.
 
I have the service manual for the PM655 non-vxi version (which is probably very close, especially the preamp section). PM me your email address if you want a copy.
 
got the manual but dont know if it will help as I am not a engineer.. I can fallow directions but thats my depth !
It does sound nice with it direct to my CD player with no pre amp
 
If you get enough gain for your purposes, you can simply leave it as it is then. At least until you find a competent and inexpensive tech. I was actually considering the same thing with my 6550 when I had problems with it, but with the power amp input low sensitivity I was getting less than 10 WPC out of it from CD. So I got it fixed after all.

Can you identify input and output for each channel on the switches and pots? Without limiting the search area further you won't be able to find the culprit. Feeding signal from CD variable output to various points in the preamp could be an easy test.
 
my Sony cdpc77 has a varible outs and I run it directly to the main amp in.. Dont think I am loosing any wattage.. Its loud and clean.. I have never heard a amp so quiet.. NO hiss at all from the speakers when not playing

I may have scored a PM 665 NOT a Vxi but my thinking is the front end pre amp boards are the same ANY input on that ! Plus its silver and I love the look of the black face and silver knobs and buttons !
 
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The background is so quiet because you've bypassed the entire preamp section.

655 doesn't have video switching and it has less line inputs than the VXI version. There are differences in specs like s/n ratio, not just power. I don't think preamp boards are the same, but it's best to compare.
 
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