HK Citation 19 amp hum r.side? what to look for

[psycom]

Hey folks, I recently purchased a Harmon Kardon Citation Nineteen Power Amp off eBay which was suppose to be "perfect" and isn't. Initial tests shows left side quite and seems perfect BUT right side has a "hum" or 'buzz' also has a small "pop" when powering down (left side was silent) and the channel indicator light is out.

I do believe the amp works. only tested with a cheap speaker and a set of rca patch cables. At first I thought the left side was bad as i had no sound but a buzz out of the right. Being a live sound audio engineer w/lots of studio time I'm familiar with equipment. Buzzing/hums aren't suppose to be there nor any pops when powering down. The seller said it work perfect for him before he shipped it.

I opened it up and looked for anything obvious but no signs of any bad wiring, etc.. only itm that caught my eye is a long rectangular chalk/off white device that appears to have a small rise/hump at the top. it connects to one of the transistors and then terminates to a small metal plate sitting between the back cooling fins and circuit board. another round cap also does the same thing. on this particular one it happens to have the overheat sensor on the transistor.

the other 3 sections which have identical parts don't show any signs of swelling. just this one which happens to be the outside / first one w/ temp sensor for the channel with the burnt out indicator light. It was piched as previously owned by a retired Los Alomos Audio engineer. you can see it and read about it at ebay...
HERE Item #290519375766

Any ideas? The amp is solid, no signs of anything amiss other than that buzz/hum which sounds like a ground problem. Plus it "popping" only on that side when powering down means a cap or resistor is out too. Maybe its that big white long thing. like an over sized piece of chalk but rectangular.

only a small portion of one side is showing any "distortion" in the shape of swelling. All the others are ruler flat on all sides. Could this be it? Part of a thermal fuse that overheated?

Haven't tried it bridged yet nor with real speakers... just a small mono one. This is a powerful amp and when I get it fixed it;ll be rockin! But need to fix myself as I don't have the cash to take it in and I can't send it back. Ebay / Paypal are useless on these matters. was hoping to find a loose wire but this is a solid amp.

thank you,

Richard

[psycom]

Read this update

UPDATE Couldn't edit original. sorry

...
I began checking caps on each side and got about the same reading. started with continuity and here's where it fails. Although the leads for the left going under the chassis (Pink & White) give my a complete circuit the same test on the right is dead. Each board where the leads connect are mirror images of each other. Tabs E1 (+53v) and E3 (-53v) on the left side have continuity but the right board does not. C9 has continuity on the left but not on the right.

after I disconnected E1 on both boards and waited 20 minutes I no longer had continuity on either side but I did through both C9's. After a minute or so the continuity came back on the left working channel but not on the right and C9 quit working again on the Right channel. All thi was done w/o out powering it up.

Right now I have it powered up and am going to let it idle for a few hours and see if that changes anything. If not, which I doubt, I'll remove the bottom and search for any visible problems. It "may" have been dropped while shipping and if so went down like a tank. But this thing is built like a tank. No cheesy soldering inside this amp!

It was pitched as previously owned Retired Los Alamos Laboratory Audio Scientist. Read for yourself and notice the power ON light in the picture is not lit up for the right channel. you can see it and read about it at here at eBay:


Any ideas? The amp is solid, no signs of anything amiss other than that buzz/hum which sounds like a ground problem. Plus it "popping" only on that side when powering down meaning a cap or resistor is out too? Hard to fathom that being from a drop. Sounds more like it had a thermal problem and took out some caps. Just guessing. I swapped fuses too of course.

Haven't tried it bridged yet nor with real speakers... just a small mono one. This is a powerful amp and when I get it fixed it'll be rockin! But fixing this could get costly and not what I bought into. So I have to figure out what to do. I really want it to work.

any ideas?
Thanks in advance.
Rich

[Hotiron]

Re: HK Citation 19 amp hum r.side? what to look for

This is an old amp I would suspect dry solder joints.
Try shorting the input cable where it meets the pcb, see if it still buzzes/hums.
The chalk you refer to sounds like a power resistor.

[psycom]

Re: HK Citation 19 amp hum r.side? what to look for

Thanks. Will get to that 1st. Luckily i have Service Manual which always helps. need to look for the points your referring to as it has a bridge mode. haven't gon into that yet but have Users Manual

Not sure if it'll do it in bridge mode. Need to check that as well. Could be how seller tried it and had noise slip by him? We'll see.

[Hotiron]

Re: HK Citation 19 amp hum r.side? what to look for

I had a look at your schematic , short out R1 150K On the pcb With the bridge switch set to stereo, If the noise goes away you will have a better idea where the problem lies.
I would still suspect dry solder joints though.

[psycom]

Re: update... smoke, white heat and quite

I'll try that idea but when i was looking to short the input i opted to disconnect the pcboard from the input instead, hooked up a speaker and turned it on.... not a peep, no buzz. i shut it down, plugged the board back in and turned it on I began hearing snaps, crackles, pops and other noises but it started to calm down then got distracted by the negative speaker output or my crimp connection seemed to be getting white. Like white hot?

looking closer the smoke made me think it wasn't normal and promptly shut it down, disconnected the speaker and checked it. 10 watt 8 ohm radio shack speaker with 18 gauge at best and I thought for sure it was fried but it wasn't.

turned it on w/o the speaker and tested the good side 1st. Yep, quite and a bit of buzz when I touched the center pin of the rca plug. cool. Then i went to the bad channel...

this time i didn't hear the loud hum/buzz. listened real close and it had an audible but slight idle hum. Could barely hear it. Tried the finger on the RCA tip trick and it worked like it was suppose to?

Tried taking some voltage measurements hoping they would be the same but were different. can't recall but the bad side was higher than the good side but still only a couple volts. this is at the output terminals. strange part is I had a polarity change as it was showing the good side as correct in a DC reading but the bad side showed it reversed? Negative became positive.

something happened. cleared out some cobwebs? not totally silent like the good side but also not whacked out like it was. Wondering if I'd ever really hear it.

Next is to hook up a mixer, some speakers and run some music through at a low volume and see what it does.

This sure was an exhilarating experience. why it did what it did is beyond me but it sure helped. or so it seems right now. and that's for the amp not me. those kinda things aren't healthy. I don't like surprises like that.

[Hotiron]

Re: HK Citation 19 amp hum r.side? what to look for

Ok so the problem lies between the input connector and the pcb.
Whoooo that was a scary reply.
Where was the smoke coming from????????????

[kaboom]

Re: HK Citation 19 amp hum r.side? what to look for

In addition to resoldering the driver board, look real close at those old diodes- CRxx. 1N914s. Observe the leads as they go into the body of the diode. Does it seem like there is corrosion 'training' into the glass body? This is real good for intermittents. CR4 and CR5, if intermittent, will give absolutely mad DC offset, popping, speaker eating, etc. If R2 on the 'Shaping Board' is cooked, that means the amp was oscillating as well.

Make sure those five diodes driving the current sink for the diff amp/LTP are good! You don't want to blow it up!

Shaping board:
L1- isolates amp and, more importantly, NFB loop, from excessive speaker cable capacitance
R1- damper resistor for L1
C1/R2- Zobel

With the driver board out, the finals have zero bias, zip- completely in cutoff. That and no path to the input was why you got nothing out.

Clean the connector between the driver board and the final! Bad connections there will really upset it- don't lose your old transistors to a loss of balance, for example. CRC 2-26 or DeOxIt...

Personally, in addition to anything else, I'd get a few dozen 4148 diodes from Mouser and replace all of 'em on those two driver boards. Especially if their leads are corroded...

Don't break that nice toy
-Paul

[psycom]

Re: HK Citation 19 amp hum r.side? what to look for

Ok so the problem lies between the input connector and the pcb.
Whoooo that was a scary reply.
Where was the smoke coming from????????????

the smoke was at the speaker connector.. the negative one. that black knob looked like it was turning white!

but what's weird is that it "seems like" it cleared up. After all that snap crackle and pop, a puff of white smoke like loads of current trying to make it down that tiny wire then it settled down. haven't been back to try anything new . Like hooking up a mixer and sending an audio signal into it and seeing ... well lets rephrase that.... HEARING what happens. I've "seen" enough.

The guy I just picked it up from says he ran it and it sounded great. I have no reason not to believe him. I don't know how long its been sitting idle either. In searching these problems out with HK's one said specifically to clean that connector and repeatedly plug and unplug it. Odd to run across that.

I'm wondering if the bridge/stereo switch is bad as getting reversed polarity out of the one side seems odd. Figured it's be putting out DC voltage and my meter adjusts to polarity
haven't read the manual as to which terminals to use while bridged.

As for the other advice or rather the way to fix it that is for someone that knows what they are doing. I'm just good at finding weak spots and making them fail. Torture testing. And I haven't even tested this yet. With caps the size of these beer cans I'm not too thrilled about getting into that without the proper test equipment, fire extinguisher or life insurance.

I also hate to go back to the seller and inform him he screwed me. It was eBay but I also used a credit card. that's not the route I want to go. If I see smoke or sparks flying again i'll change my attitude.

I have a HK PM660 that I don't use as it is. Figured I could bridge this and run my PA. Now I need a tech In Knoxville TN. Mines in California. .

But thank you for all the pointers. I will look at them all carefully and get my rubber suit on and try a couple things out. I need to find the previous owner that took such good care of it and ask him what the hell the deal is.

keep em comin. especially if you're within driving distance. I may need a repair tech.

[psycom]

Re: HK Citation 19 amp hum r.side? what to look for

In addition to resoldering the driver board, look real close at those old diodes- CRxx. 1N914s. Observe the leads as they go into the body of the diode. Does it seem like there is corrosion 'training' into the glass body? This is real good for intermittents. CR4 and CR5, if intermittent, will give absolutely mad DC offset, popping, speaker eating, etc. If R2 on the 'Shaping Board' is cooked, that means the amp was oscillating as well.

Make sure those five diodes driving the current sink for the diff amp/LTP are good! You don't want to blow it up!

Shaping board:
L1- isolates amp and, more importantly, NFB loop, from excessive speaker cable capacitance
R1- damper resistor for L1
C1/R2- Zobel

With the driver board out, the finals have zero bias, zip- completely in cutoff. That and no path to the input was why you got nothing out.

Clean the connector between the driver board and the final! Bad connections there will really upset it- don't lose your old transistors to a loss of balance, for example. CRC 2-26 or DeOxIt...

Personally, in addition to anything else, I'd get a few dozen 4148 diodes from Mouser and replace all of 'em on those two driver boards. Especially if their leads are corroded...

Don't break that nice toy
-Paul

OK... I see what you're getting at. I can do that. But remember I said I had hooked that board back up and after the fiasco it settled down.

But I understand what you're saying. Just didn't read it closely as its late. Thanks a million for the advice! And as far as how things looked... nothing appeared bad anywhere. I am familiar whit what failed or failing parts look like. I've fried a few things in my day.

I had no fear... but then I drank a lot back then. It was easier!

Thank you for your help.

rich

[psycom]

Progress.... gettin better

Kaboom... did what you suggest and ALL the diodes look fine. I sprayed down everything, cleaned those board connections... repeatedly too, both of them.

The shaping boards are intact with no signs of anything ever happening.

Powered back up and did the routine speaker check.... still just a slight buzz on the right side like after all the excitement but nothing like it was. It was LOUD before. This is like idle or interference noise such as what you hear from a fluorescent light but it's NOT that or both channels would do it.

Now for something new.... tried the bridge mode. Turned off, flipped the switch (I cleaned that as well) and turned on. Hooked up the speaker and there was that loud buzzing again. Shut it off flipped the switches same as before in stereo, went back to bridge and yep it was buzzing ... then it began to fade away... and it faded into silent bliss!

Tried the input finger trick and yep it worked. So I powered down and did it again. Same thing but not as loud and faded quickly into silence. Right now it's on in the bridge mode and I'm just gonna let it run over night w/o anything hooked to it. Let it balance out, get use to having power to it.

Later tomorrow (today) I'll recheck it. I'll also try what Hotiron suggested: "short out R1 150K On the pcb With the bridge switch set to stereo" and see if the noise goes away if its still there.

My PM660 has an idle up period before the amp kicks in. Does this have that? If it did I might not have heard the buzzing in the bridge mode when I fired it up.

also...
"Make sure those five diodes driving the current sink for the diff amp/LTP are good! You don't want to blow it up!"

HUH? I need to look at the schematic to figure out where this/these are? and "LPT" = Lost That Part right? Need to find it. Sorry but I'm self untaught and went to public schools to boot.

Oh... there's a pretty awesome looking Citation 16 on eBay right now. Item # 220739301290 at $400.00. Reading up on it I can see problems ahead as its not an "A" an they make a mod for it.. But overall it looks pretty damn serious. 400 bucks with one guy really wanting it. I pushed him u that high and there's 4+ days to go.

Thanks to both of you guys!

Rich

[psycom]

Right LED is now flickering...

The dead right LED began flashing a little bit ago. It's connected to the thermal circuit breaker and when tripped that LED is off and so is the power to that side... supposedly. It's trying to come back on but hasn't hit full glowing status yet.

Checked the voltage readings and tried to adjust via VR1 but never hit 77ma unless I take one leg from the VR1 and go to one leg or R5 then I can get it adjusted correctly.

slight buzz still in right channel but none when bridged. The light is trying to tell me something. Like... HEY! I need professional help! somewhere along the line it had a big

does this send me down a different corridor?

[psycom]

this thing sucks. blew a speaker I'm pissed

Well I put signal into it and had a barely audible sound. Tried a different signal and never heard squat but it toasted my speaker!

Hooked up a 100 watt guitar speaker to it and it's buzzing like at first w/o an input. Put it in bridge mode and it has a hum to it.The "burnt out Led" (r) is still flashing away. shut it off and it nearly blew that speaker with the big old POP. It quit doing that until it tried to process a signal. Now it's back to the way it was.

This is bullshit. I contacted ebay. This needs a rebuild. Lucky it didn't start a fire. Seriously pissed for all the hours I have into it not to mention money. Te flashing led that came back to life tells me it wasn't something that happened during shipping. The photo in the ad shows it not lit up.

I think it overheated at one time as it all consistent with the thermal sensor. God only know what else it took out or is about to go.

Oh well, I tried. If anybody wants it follow the ebay link and contact that seller as he'll be getting it back. This will take awhile but I'm over it now. 4 hours bench time, blown speaker, sparks and smoke from an amp that is in "Excellent shape." Now it took out some of my recording gear in the process... the mono mix down speaker.

That did it. I'm off to buy an amp I can use while I deal with this. It ain't gonna be my problem anymore.

Thanks for all the help guys. If it was what it was advertised as I would have a piece of art... history. This is a fire hazard boat anchor. Its obvious the seller didn't run a very through test on it. Heck, he didn't even take those pictures... he never notice that half the amp was out.

Rich

[kaboom]

Re: HK Citation 19 amp hum r.side? what to look for

That's how it is on fleabay.

No one knows how anything is s'posed to work- those overheat LEDs in your case. Yet they take pix and give 'proof' that it's 'working perfectly.'
Yet the pix showed otherwise...

If ebay/payfail bullshits ya, and you want to tame this beast, send that thing my way. Fixing a tough dog like that tends to make my day, and I enjoy seeing ebay specials fixed. Yet you shouldn't have to deal with fixing something that was understood to be working.

Good luck
-Paul

[psycom]

Re:parts have been replaced before

That's how it is on fleabay.

No one knows how anything is s'posed to work- those overheat LEDs in your case. Yet they take pix and give 'proof' that it's 'working perfectly.'
Yet the pix showed otherwise...

If ebay/payfail bullshits ya, and you want to tame this beast, send that thing my way. Fixing a tough dog like that tends to make my day, and I enjoy seeing ebay specials fixed. Yet you shouldn't have to deal with fixing something that was understood to be working.

Good luck
-Paul

Thanks for the offer to help. I'm still trying. have the driver board off and see that Q5 has been replaced. What is that used for? P2 pin #1 looks odd... sticky stuff around it on the pcb.Before I got that far I took off the heat sensor and did some more cleaning all around tightening things down and last check the front LED light is getting steadier.

Bought the cleaners you suggested and am going to clean things up better and hit some points with the iron. Reassemble and see what happens.

Ebay settled in my favor and I just need to ship it back and I'll get a full refund. They even gave me pre-paid label. Surprised the hell outta me. But I really would like it to work so I'm giving it this a closer look and clean it up better. The P1 & P2 tabs are much easier to do now.

I'm still leaning towards the fact it overheated once. Maybe it took out the Q5 then. who knows. everything else looks stock. At this point if it began working I'd be wary of it pulling a stunt outta the blue and causing more damage.

If it didn't weigh so much I'd ship it to you and let you go over it. It's be right, I wouldn't have to worry. That was a great gesture on your part. If I can ever repay the favor just ask.

rich

[psycom]

Re: HK Citation 19 amp hum r.side? what to look for

RESOLVED:
In the end I had to return it and the guy accused me of changing out the power caps! This after he'd supposedly purchased it from some scientist. When I replied "oh then so you DID open it before!" that was the end of ever hearing from him again.

You guys were SO helpful I couldn't let it pass without a final thank you! Took me years to do it but I never forgot any of you.

Richard