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9090DB Outputs

bobforapples

bobforapples

Angular banjos sound good
I have been working on a 9090db for the first time, and I am learning alot from reading old posts in this forum.

I am replacing all the fusible resistors with metal oxide flameproof, and I'm going to re-cap the driver and power board. I won't be using Dolby so I do not plan on touching that troublesome board.

I tested the transistors on the driver board, and they all test fine, I got wierd results on the two that are mounted on the top of the heatsinks, but both sides matched. I think the wierd results may be because of where they are in the circuit.

Before I start to order parts, are these the "output transistors" people talk about replacing?

Thanks!
 
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I guess I should re-word this.

Are there other transistors that would cause failure of the fuses on the power relay circuit board, F-2657?
 
No, those are the driver transistors for the outputs. The outputs are on the big heatsink on the back of the receiver. If those are good your driver board is likely ok.
 
The only thing that will blow the fuses that you are talking about is a shorted protection relay or shorted speaker wires. These fuses are after the outputs, shorted outputs will blow fuses on the power supply board. If these fuses blew then check the protection relay and make sure it does not have the contacts welded together, If so the outputs will be shorted to ground and will blow these fuses that are on the protection board. Newer units don't have the fuses.
 
I think the protection relay did click on and off, and I got a green light, but I'll check the relay anyways. After I test my outputs I'll start re-capping and de-fusible-resistoring.
 
Not knowing the history of this receiver, I think it's a good idea to check everything, so....

When I turned it on, the red light blinked, I heard a click, and the light turned green. Wouldn't this prove the relay is working properly?

Also, upon checking the output transistors, I had some funny results, so I decided to pull them out of the circuit and try again..... After I pulled off the rear heat sink, I noticed 7 of the transistors are Toshiba, and the other, I have no idea... it has a large S on it.

Either way, 8 new transistors are in order.

I searched the forums, and I'm still not sure which transistors to replace them with. Any suggestions?

Thanks.
 
bobforapples I belive MJ1193 and MJ 1194 are good replacements for you. I belive these will work just fine but a second opion would be in order. search these transistors out in this forum . I used them in my AU919 with good results englissa
 
Well, the Toshibas are not factory originals, and they don't work. So the MJ21193 are sounding like the way to go.
 
bobforapples said:
Well, the Toshibas are not factory originals, and they don't work. So the MJ21193 are sounding like the way to go.
Click to expand...
Where did you hear that? Toshiba 2SD424 and 2SB554 were absolutely factory original in the 9090DB. Anything else is a replacement. Just look in the service manual if you want to get another opinion.

- Pete
 
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