View Full Version : Blew it and need help!!!`


Detailman
05-15-2007, 02:44 PM
A while ago I tried to change caps on the amp boards on my 2230 and managed to destroy the diode SV-3[heat sink diode] on the left channel.
Well after finding out they are un findable I got some NTE605A[reccomended on AK searches] and tried them.
I can get the channel to work but output is lower and has a constant hum.
I was just checking some things and measured between J753 and J754[where the diode connects] on the good and bad channel.
Using the diode setting on my DVTM I get 1.2___ appr.on the good channel one way and 0v the other as I think it should be.
On the bad channel[left] I get 1.7__ app. one way and .7v the other.
Doesn't matter if the diode is in circuit or not.
Don't know if this is a real measurement but it seems to me that both should measure the same.
I'm not good at reading schematics but I'm attaching a copy of what I have.
Maybe I've got another bad diode that's not cutting off voltage?
Definitely a guess but I'm hoping I can get some helpful opinions!!!!!!!

Thanks

John

EDit. I tried to post my copy of the schematic but it got lost in the shuffle. When I check my attachments it's there but I don't know how to get it to here.
Strange.

EchoWars
05-15-2007, 06:52 PM
The diode is there to help set up the bias current, and to compensate for temperature changes. You fail to mention if you can measure and set the bias current.

Nakdoc
05-15-2007, 07:04 PM
The SVT-3H is the equivalent of 3 silicon diodes in series. In a pinch you can substitute, but the thermal bias tracking will be compromised. You can probably find a parts unit. As for measurements, out of circuit your meter cannot forward bias it, so it should read open in both directions. In circuit, the voltage ought to be about 2 volts, however it could be lower. As EW said, what bias voltage do you read on your output emitter resistors?

Detailman
05-15-2007, 07:40 PM
Guess it's obvious I'm a little over my head here. Let me get a copy of the service manual.
EW. I really haven't tried to adjust the bias. Would that account for the difference in voltages?

Nakdoc. Thanks for the info on the three series diodes. I'll try to look for a parts unit.

Fred Longworth
05-16-2007, 09:18 PM
The original part was THREE compensation diodes in series. The NTE605A is TWO compensation diodes in series. This works fine for the Sansui 5000A to replace the horrible black compensation diodes mounted on the drivers, but does not work for the SVT-3H. However, if an NTE600 (if still available) is placed in series with the NTE605A, this will give you the three diode drops you need.

Fred Longworth

Detailman
05-16-2007, 11:52 PM
The original part was THREE compensation diodes in series. The NTE605A is TWO compensation diodes in series. This works fine for the Sansui 5000A to replace the horrible black compensation diodes mounted on the drivers, but does not work for the SVT-3H. However, if an NTE600 (if still available) is placed in series with the NTE605A, this will give you the three diode drops you need.

Fred Longworth

Thanks Fred.
That really explains it. I'll do some searching for the 600. I got the last 605A's the seller had.