Marantz Model 26 Pops Fuse

[Tala Mink]

I recently started working on a fuse blowing Marantz model 26 for a friend.

I have looked for at the usual causes but the only problems I can find are the filter cap, which started leaking after I pulled it, and the 0.5ohm resistors connected to the output transistors read open line.

I have checked all the transistors in the amplifier section and all test fine except one with slightly lower than average gain.

So my question is if I replace r47-450 and do a partial recap will the amplifier power
on or could there be more to the problem.

Also the model 26's fuse has a reset button, is there an actual fuse in there or does it trip like a circuit breaker?

 

[avionic]

and the 0.5ohm resistors connected to the output transistors read open line.

This is normally the case with a shorted output transistor when emitter resistors burn open.

Did you receive this piece in this condition ? Do the output transistors look OEM ?

 

[avionic]

Welcome aboard Tala.. PS ... Your schematic image is useless. To small to read.

 

[Tala Mink]

Welcome aboard Tala.. PS ... Your schematic image is useless. To small to read.

Sorry its supposed to be the 0.5ohm resistors.

Also the output transistors (H001-H004) are 2SD257 and look original though I cant find them in the parts list.

 

[petehall347]

my schematic calls for 0.24 ohms ..

 

[Tala Mink]

I will remove the output transistors to test though because is have only seen resistors blow due to shorted outputs.

Edit: I just pulled both output transistors in the right channel and tested them with an atlas dca 55 instead of a multimeter and they test completely fine.

 

[Tala Mink]

Probably last post on this thread, the filter capacitor is in fact shorted, it was the second thing I suspected but last thing I looked at.

my schematic calls for 0.24 ohms ..

The schematic I got on Hifi engine also says that but the 1/2 ohm resistors are original so it was likely implemented in production after the schematic was made.