Sansui 9090DB Restore Part 6 Power, Relay and Alignment

[@poormanselectronicsbench2021]

It's always best to read any detailed notes in a service manual before proceeding on tinkering with it. If you ever work on a Harmon Kardon Citation Sixteen amp, and you think its way too hot when idle, a detailed read of the service manual ( A series, pages 5 & 6) states that it's biased high to run the outputs into class A at a higher level, because they stated they did some research and found that some perceived audible distortion was reduced/eliminated by doing so. The result is, the heat sinks can be up to 60 Degrees C at idle, ( 1/3rd power could be 80C, and full output 75C) but are large enough to cool it well, if kept in an open area.

[@raygianelli3612]

That's a good point, and kudos to Harman-Kardon to put those notes in there. Most audio service manuals are pretty skimpy on details, so the exceptions to that are welcome indeed! 60-80°C is blazing hot! I imagine there were cases where they weren't kept in an open area and failed simply for that reason.

[@poormanselectronicsbench2021]

@@raygianelli3612 There were at least 2 "Service bulletins", on it, the only 2 that are currently searchable were to address issues with the protection relay system, which, they originally designed as just a delay for connecting outputs to the speakers, then, they added DC offset protection, then, they disabled the DC offset protection and added a "input limiting" diode network. There's no telling why they regressed away from the DC protection, but IMO, the original relay was under rated ( Potter-Brumfield R10-E2W2-V185 , only 7.5A rated contacts, and its still available, amazingly) , and they were probably finding that if it was forced to operate under full load the contacts were getting roached.

[@andymouse]

Great work and I feel your pain (Dentist !)..........cheers.

[@raygianelli3612]

Thanks Andy. The only thing that hurts now is my credit card. Worth every penny though!

[@coldfinger459sub0]

Thanks , always learning from your videos

[@raygianelli3612]

Thanks Tom! I just subscribed to your channel because air conditioning is something I don't know enough about.

[@roroseppel2077]

Hey Ray, even blown fuses are usefull ! Nice video !

[@raygianelli3612]

Thanks Roro. Now if I could just find a use for my dead battery collection...😳

[@bill_p2074]

You always want to charge something you will enjoy - not the dentist! 💸

[@raygianelli3612]

Bill, while I basically agree, not having a toothache is priceless!

[@bill_p2074]

@@raygianelli3612 in your recent reply to me you mentioned being in a 11 story building. Is that possibly the old 4A toll building?

[@raygianelli3612]

@@bill_p2074 I don't think so, Bill. This building was built because the old building next to it wasn't big enough to contain the growth, probably in the early 80's. Eventually they moved everything to the larger building and sold off the old one. It's been converted to loft apartments.