Hello everyone,
I just purchased a pair of Kenwood L-07MII mono blocks. One works fine. The other was known to be a problem with overheating within 10 to 20 minutes of operation at the time of purchase. When I got the pair I took the one which was a known problem and opened it up. There were no noticable surface injuries (burned resistors, failed caps, etc). I have the schematic and a portion of the service manual I found out on the web which shows how to measure the voltage, dc offset and bias. The voltage was spot on at -/+ 60v and the DC off set was ever so slightly above 0v and I returned to the proper 0v. The bias was wierd. It came up VERY SLOWLY. At 25mv bias it took about 5 minutes to come up to that from start up without any load on the amp. Once up to 25mv I let it run for 15 minutes with no load. There was no noticable heat at all. I shut her down and hooked her up to my CD player and JBL speaker. Turned it on and played Dire Straits and within 2 or 3 songs she was hot to the touch on the heat sinks and since I had the top cover off I touched the transistors and they were hot enough that it was tough to keep the figures on them. Any suggestions? Unfortunately I no longer own a scope. I was thinkng about the possibilty of ocsillation at the output? Again any help would be appreciated.
I just purchased a pair of Kenwood L-07MII mono blocks. One works fine. The other was known to be a problem with overheating within 10 to 20 minutes of operation at the time of purchase. When I got the pair I took the one which was a known problem and opened it up. There were no noticable surface injuries (burned resistors, failed caps, etc). I have the schematic and a portion of the service manual I found out on the web which shows how to measure the voltage, dc offset and bias. The voltage was spot on at -/+ 60v and the DC off set was ever so slightly above 0v and I returned to the proper 0v. The bias was wierd. It came up VERY SLOWLY. At 25mv bias it took about 5 minutes to come up to that from start up without any load on the amp. Once up to 25mv I let it run for 15 minutes with no load. There was no noticable heat at all. I shut her down and hooked her up to my CD player and JBL speaker. Turned it on and played Dire Straits and within 2 or 3 songs she was hot to the touch on the heat sinks and since I had the top cover off I touched the transistors and they were hot enough that it was tough to keep the figures on them. Any suggestions? Unfortunately I no longer own a scope. I was thinkng about the possibilty of ocsillation at the output? Again any help would be appreciated.
