Vintage HK protect mode?

pizzigri,
 http://audiokarma.org/forums/index.php?threads/citation-22-in-protect-mode.325835/
schematics:
 http://akdatabase.org/AKview/albums/userpics/10004/Harman%20Kardon%20Citation%2022%20Schematic.pdf

Hello everybody, first post.... and it's for a problem. Can anybody help me located the mod to the circuit board that Lynne mentioned in the post, I have a Citation 22 that I am trying to fix and I believe it suffers from that circuit mistake.

All my b est,

franco

I've got the same Citation 24 and just the other night it froze with the protect light on. Could you pass along the contact info for the tech that had fixed yours?
Thanks,
Steve

Thanks. I might have added that I'm a little surprised by the sound quality. I like the new stuff and I bought it as a gift for someone who likes vintage. It's soft and full and quick. I can understand why the owners have no desire to upgrade. I wouldn't either.

Sounds good. I hope you enjoy it.

Getting back to you guys on the Citation 24 protect mode after getting it back from the tech today. Tech's note: Located and replaced 2 faulty capacitors in protection logic circuit.

I think I found a good tech. He says, disassembled and cleaned pc boards and chassis. Pulled speaker output jack. Plastic broken and cracked. Fabricated support for speaker output jack and jack panel. Checked components for correctness as much as possible. Bias is dead on. Resoldered a few suspect connections on output board. Inspected driver/regulator board-ok. Reassembled and bench tested. Works great. Flat rate $90

For anyone who might be interested, from the research and anecdotal info I found, I believe that the quality control issue regarding the factory bias settings is misinformation. A source who is an agon member told me that the left channel bias circuit board contained an error on both the 22 and 24 which does not agree with the schematic and which he found and corrected on his own amps.
I have run into owners on the net whose amps ran hot and the left channel subsequently burned up. I believe that at some point in production Harman found the error, if not before, then after the amps started burning up, and corrected it during production. Otherwise, I don't think there would be any 22's or 24's left.

Regards,

Lynne

OK. Thanks. I have a tech lined up who loves to work on vintage.I never thought of that--the click. Like a solenoid. The click can wear out. Cool. Thanks.

In general, I'd say NO. Not too hot, since when turned on, it's stone cold.

Too high a bias? Don't know if that could trip some protection circuit. Maybe if the circuit 'interprets' that as a short? That'd do it.

In any event, a trip to a tech is indicated. Choices are stuff like bias adjust, or time delay relay problem. Weak output device, going bad? Don't know.
Such relays are fairly reliable, but also a moving part....That click you ordinarily hear is the relay 'flipping'. which means it can wear out.

OK. I'm making a list. Thanks. I'll ask a dumb question just to illiminate it: The only info I've been able to glean from the net is that, while build construction was high quality on Citations 22 and 24, the bias settings were all over the map so that quality control was an issue in this respect. Some were set so high that when the amp was driven hard, it burned up. Could a bias set way too high tell protect mode that it was too hot to turn on?

It is just possible you are talking about a discrete 'time delay relay' which best case, is socket mounted.

OK. Thanks. I can't get back to you yet because I don't have the amp yet. It is being shipped. But this is very helpful.

There were some Harman Kardon amps that went into protection mode if the preamp was giving some DC to its inputs. I can't remember model, or how many years back I heard about this. Maybe trying another preamp (no preamp if you feel safe) to see if this can be a problem. I can't remember if this happened right at start-up, or after the delay (few seconds?) turned the amp on, then went into protection.

Yes. The warmer the ambient temp, the longer the delay--up to one half hr.

How long a delay are you experiencing? More than 10 seconds? I recently had a very long delay -time issue with an NAD receiver that finally stopped kicking in altogether. After a little snooping I replaced a small capacitor that was located right next to the relay, thinking that it set the time constant for the relay to kick-in. On Power-up, the receiver stays in protect mode for about 4 seconds and then latches on as it was designed to. I would look for a similar situation in the HK. In the case of the NAD it was a 1uf at 50v electrolyitic capacitor. If you can find the service manual for the amp, it will show you the components around the relay for possible clues. Also, there is a thread at Audiokarma that tells how to check the dc offset values at the output of the amp. DC offsetthat is out of spec can cause an amp to go into protect mode, and is worth having a look at either way (if you're interested in a more hands-on appproach to maintaining your gear).