Thread: Quad 405-2 help
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Old 2nd Jul 2019, 12:42 am   #31
Top Cap
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Join Date: Mar 2006
Location: Watford, Hertfordshire, UK.
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Default Re: Quad 405-2 help

I have had the misfortune of getting one of these for repair
Yes our dear friend the 3k3 resistor R7 had gone open circuit, probably crippling the op-amp and taking all the power devices and fuses with it. I have been able to order suitable replacement parts but I suspect one of the current limiters has gone on vacation too. I have not been able to find any of these even Dada have no stock so plan B is to build one (maybe two?) on isolated pad prototyping board, necessary to keep physical size down. Just when I thought my Pin and Wire days were long gone.
I just hope the ubiquitous 2N3904 and 2N3906 will be OK.
Just in case anyone else has this problem I will attach my sketches so far but bear in mind they have not been built yet but confidence here is running high

Suggested build is to fit all components as shown in parts placement, hopefully there is more room than indicated! Wire for pins can be 20 SWG tinned copper such as RS 355-063. Note how it is threaded from component side then routed back (Pads F & G) to give good support and prevent pad lift.
Short links can be made using solder at:-
1A to 1B, 1E to 1F & 1G, 1D to 2D, 2E, 2F & 2G,
3G to 4G & 4F, 3D to 3E, 4C to 4D,
5F to 5G, 6E to 6F & 6G.

Fine wire links can now be added at:-
1A to 4A, 1B to 2C, 2C to 1E,
1C to 2A, 2A to 6C, 2B to 5D,
3A to 5A, 3F to 4E, 4F to 5C,
5E to 6D, 5F to 6A.

Give me a good Valve amp repair any day - Current dumpers indeed!
Attached Thumbnails
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