QUAD Amplifier Repair Part One

QUAD 1980's Apmlifier Repair. - It's a LONG ONE, so myou might want to SKIP bits.

A viewer of my channel got in touch to say he'd dug his old QUAD Amp out of the loft and it needed checking and repairing as it hadn't been used in a while and might have one or more leaky electrolytic capacitors that need changing. Other than that, it looked to be OK.

Once it arrived, and I'd unpacked it, it did indeed look OK externally but internally there were some definite capacitor issues, not to mention that one half of the power amp had been disconnected from the positive supply rail. I suspect the amp had failed and a repair had been tried but failed. The power amps can be very sensitive and whilst it has a unique "Current Dumping" circuit, designed to protect the loudspeakers from a fault, if the circuit is triggered it can kill the output stage. I suspect that's probably what happened sometime in the past.

So the "Simple" recap job turned into a major repair as well. I hope the video gives you a flavour of the task I undertook, I've edited the video - part one of two - down as much as possible but I spent an inordinate amount of time on it, over several weeks.

The last problem was my fault, luckily, this didn't cause any further damage and proves that cold checks and the use of a variac is good.

Part Two - the pre-amp unit - coming soon.

Enjoy


CONTENT:

00:00 - Introduction
02:02 - Looking inside the units
02:53 - Admiring the wiring workmanship
03:45 - Begin capacitor inspections
06:05 - Start work on the power amp unit
09:23 - Testing the caps
16:05 - Making a shopping list of caps
17:50 - Beginning the replacements
30:08 - A PCB screen print error is found!
38:42 - Caps changed begin testing
42:37 - Fresh start fault finding
47:00 - One channel is OK!
57:11 - Replacement parts arrive
1:09:43 - Parts fitted now cold checks
1:12:41 - Another faulty component found
1:20:52 - Replaced it and more testing
1:22:01 - Testing shows another fault!
1:28:17 - Another day and more cold testing to do!
1:33:21 - Found it - hey, everyone makes mistakes!

Luckily, this didn't cause any further damage and proves that cold checks and the use of a variac is good.

Part Two - the pre-amp unit - coming soon.

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