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AU-101 lifted/damaged pad repair

S

skippy124

Super Member
Hi,

I recently received an AU101 for repair - it had been purchased by the current owner from "an enthusiast" that had done some repairs and a partial recap, and had failed not long after he took ownership.

The fault was fairly simple to diagnose and repair - both rectifier diodes had failed and had taken out the two internal fuses.

However, the previous repairs were not very well carried out - three of the driver transistors had been replaced with BD139/BD140's, and some pad and track damage was evident on two of the replacement transistors

All three pads damaged



Collector pad lifted



Top view of the two replacement transistors that had pad problems



so it was time to go to work and repair this damage, using these




After removal of the worst transistor, and one copper ferrule fitted



The other transistor removed and a ferrule fitted to the collector pad



Picture of the replacement transistor (topside) after all three pads had been fitted with ferrules



picture of the bottom after resoldering of this transistor (the other repair is to the upper left of the picture - the new transistor yet to be fitted and soldered)



This is the first time I have used the copper ferrules, it was an easy repair to do, and I was very happy with the result.

This unit was then completely recapped (except for the main filter cap), multiturn pots fitted.



The screw speaker connections were also replaced with binding posts







She has had a good run on the bench, and afer completing a clean and detail it will be sent back to the owner and hopefully it will give many more years of service (and listening pleasure)

Cheers

John
 
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Nice work as usual John, with a particularly excellent track repair. :)

Tell us about the resistors across the fuses... :scratch2:
 
SansuiSteve said:
Very tidy work. Where did you get the copper ferrules?
Click to expand...

Hi, thank for the kind words. I got the ferrules from RS Components (Newark in the U.S.). I think they may also be available from either digikey or mouser too. These are the small ones 0.8mm internal hole, requires a 1.3mm hole in the PCB. The larger size - from memory - is 1.1mm internal hole, and these require a 1.8 mm hole.

Cheers

John
 
Hyperion said:
Nice work as usual John, with a particularly excellent track repair. :)

Tell us about the resistors across the fuses... :scratch2:
Click to expand...

Thanks John.

Re the resistors across the fuses - these are blown fuses that I have fitted 1 ohm resistors, you can then do a bias current measurement at the fuses as per the service manual by measuring the voltage across the resistor, and calculating the current - easy in this case as mv = ma. Saves meter fuses, and making a voltage measurement is generally safer than making a current measurement,

I also have some 20x5 fuses with the same set up, and I have found both to be really helpful in setting the bias current in amp that have a fuse current value.

Cheers

John
 
Hi,

The amp has been cleaned and detailed and is ready for packing and shipping back to the owner.

This unit is a late build 101 (May 74) and has a silk screened front panel - earlier build units have an engraved front panel.

Note that the front edges of the side panels don't have any chips in the veneer - just about every 101 that I have seen as at least one chip.













Cheers

John
 
Excellent repair work, John. I like the way those ferrules hold the track down, it looks a very permanent fix. What a great looking the amp! And great photos, too.
 
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