Quad 405-2 Amplifier Blown Channel Repair

The Quad 405-2 that I refurbished a little while ago blew a channel.
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In this video I repair my Quad 405-2 after it blew a final transistor, and track down the culprit that caused it to blow.
You can support my work on Patreon: patreon.com/audionautica
Check out my watchmaking channel: ‪@watchout9213‬
Music is Asher Fulero, Pouring Out, from the KZbin audio library.

[@jetblakink]

Just bought one of these… Love it!

[@audionautica6843]

Awesome!

[@max79444]

A nice investigation and repair..

[@audionautica6843]

Thanks!

[@poormanselectronicsbench2021]

What would be your best guess on the component that started the failure? I'm guessing it was one of the 15V Zener diodes that got tired, but what do I know? It would be interesting to take them up to their max current for a bit and see how they act. Too bad you had to go back in, but at least your speaker protection add-on and the fuses did their job.

[@audionautica6843]

Yeh, who's to know. I read on a few forums about the Zener getting tired so that may well have been it. My hope is there isn't some other issue hiding behind the scenes that will pop up again requiring a third go.

[@CrazySparkie63]

I always replace the Zener's with 1.3 Watt ones as recommended by Quad!

[@johnmurphy6880]

Thank you, really helpful video, well done 👍🏻

[@audionautica6843]

Thanks for watching!

[@richarddavey9547]

Hi , great informative video, I'm just in the middle of recapping one of these using your videos as a guide, my question is the two Nicichon Muse caps you have fitted are bipolar where as the originals aren't, am I ok to fit two muse bipolar caps ? And what value are those two caps please? Thanks 👍

[@audionautica6843]

Yes, they are fine. I have made the Bill of Materials available for my Patreons. If I recall the value is the same as the originals.

[@richarddavey9547]

@@audionautica6843 Thanks for your help 👍

[@Pauloroberto-tl9pm]

very good

[@giovannipg3000]

Nice done 👍

[@tweakerman]

Nice Job!

[@audionautica6843]

Thanks for watching @tweakerman.

[@HowardJohnstone]

Please read up before posting, as these faults are all classical. The R7/8 that caused this fault, must be replaced by at least 1W 3k3 or it will blow again. The classical faults are different related to PCB rev.

[@audionautica6843]

I did and I have, but I will check it again...

[@oldskeptic1513]

... a DC level on the output, if any, ought to be in mill volts ... another thing, you've fitted yet another pair of bulk capacitors even though you put a pair of new ones in the previous video ... why ?

[@audionautica6843]

Two different amplifiers mate. I left the originals in this one as they tested fine.

[@ewhibs]

Hello, can you tell us what the function generator program for your iPad is? Thx!

[@audionautica6843]

I found it on the App Store, just find one that looks like it will work for you - I think it was free.

[@xXBantamXx]

Can my Quad 405 be upgraded to a 405-2?

[@audionautica6843]

I've never worked on a 405 myself, but my understanding is that over time the 405 evolved into the 405-2. Ie, the later 405s had seperate protection boards which where then incorporated into the main PCB in the 405-2. The service manual shows the various difference. There are also some pretty good web sites out there about the 405 and 405-2. They also talk about various ways of "improving" 405s.

[@flufycat2748]

nice.

[@ladronsiman1471]

Bravo .. I hate British politics .But i love British engineering .. I love Quad amps and speakers ..And cars .... I will now go to a German site and tell them the same story .

[@audionautica6843]

🤣

[@grattanvaz1614]

Wgat the hell. This amplifier has glass epoxy boards.

[@viperwizard491]

carbon resistor

[@padgepadgham3238]

Good work, but even fully rebuilt, they sound awful compared to good amplifiers.

[@audionautica6843]

Beauty is in the eye *ear* of the beholder. I haven't used mine a lot for HiFi, have noted it is a bit bass heavy IMHO. These do have a cult following. There are some in the know much more than I who would not agree that these don't sound good. See here: liquidaudio.com.au/quad-405-power-amplifier-review/