Quad 606 Repair

Heey guys, I am trying to repair one channel of my Quad 606 power amp.

Initially, I found that T9 had blown and shorted itself out. All terminals pretty much measuring 0Ω between each other. So I removed it. I also replaced R38 (2k2 in the top right corner which was burnt).

I replaced the fuse and turned it back on (still without T9) and the next one (T10) blew short straight away.
I am guessing it’s something to do with this T15/T16 voltage reference network, but I can’t easily just remove the load to test it without cutting traces.

Do you think I should I just try to replace T15/T16 next? Any suggestions for modern replacements to the ZTX652/752?

Thanks a lot!

Your dealing with a direct coupled transistorised circuit here , if theres something amiss or blown it often causes a chain reaction down the line , finding the service manual would be a good plan if you dont have it already ,Quad may be able to suggest replacement output transistors for it ,mixing and matching different kinds of output device isnt a good plan either . You may have to remove the output transistors to find the duds as there all in parralell. You have one working channel so compare readings from the working side and the blown side ,dont bother trying to power it up until everything is right .

Tubetec said:

Your dealing with a direct coupled transistorised circuit here , if theres something amiss or blown it often causes a chain reaction down the line , finding the service manual would be a good plan if you dont have it already ,Quad may be able to suggest replacement output transistors for it ,mixing and matching different kinds of output device isnt a good plan either . You may have to remove the output transistors to find the duds as there all in parralell. You have one working channel so compare readings from the working side and the blown side ,dont bother trying to power it up until everything is right .

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The output transistors that were already in there are modern replacements anyways. The only way I found the blown transistor was by measuring them while it was turned off, and then removing them one by on from parallel til I got the shorted one. I assume that it doesn’t actually need all 3 of these output transistors (T9, T10, T11) to turn on if I’m not driving large output currents right?

I found the service manual this morning but it didn’t offer much help except suggesting that it has something to do with that 2k2 I replaced, and it’s complimentary part on the other side. I think I will replace T15/T16 and the shorted output transistor, and if that fails I guess I will have to try to find a way to isolate this T15/T16 reference circuit to see that it’s actually producing the correct voltages without a load.

Unless someone has a better suggestion?

As I said I wouldnt power it up unless everything is right ,bias and standing currents would be off with parts out of circuit ,you may get away with it ,but it could also just go 'poofffff' and just end up doing more damage.