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Restoring an AU-X1

Hyperion said:
And now for a progress report.

As I previously mentioned, I was unable to set right channel bias, and while making measurements to compare the channels I did something to the left channel which caused the same effect. I am happy to report that I have restored the ability to set bias on the left channel, (shorted TR16 replaced) and begun working on the right channel this morning.

Here is a picture of the right channel heatsink, showing the right channel OP transistors only.
View attachment 717120

And a picture of the right channel driver board - completely untouched by me. (apart from desoldering various connections to be able to remove the module).

View attachment 717121

Having taken as many voltage and resistance measurements as I could with the module in situ, I set about finding out what was wrong - expecting as with the left channel a shorted or open transistor. Knowing I could set DC offset ruled out the input FET and nine other transistors, leaving 7 to look at, I went through them all checking with my multimeter on 'diode test' and found nothing definitely wrong, but a few weird readings made me remove several to double check with my Peak Tester - all seemed good. I checked that the bias trimmer actually adjusts, and checked all diodes - all good. I checked the emitter resistors of TR10/11, TR15/16 and TR13/14, all good - and began wondering if I had some nightmare fault, like an intermittent transistor or something.

Then my eyes fell upon R36 and R37, they have the look of 'fuse resistors' (although they aren't) but otherwise look innocent enough, 390Ω - so I checked them, one measured 211KΩ and the other one was open :yikes: - take a look below - the base stoppers for the driver transistors both effectively open!

View attachment 717124

I am left scratching my chin as to 'how' these came to be like that - needless to say I'll be checking the other channel as well. I learnt a lot finding these faults, I now have some extra tricks up my sleeve when troubleshooting similar amplifiers. ;)

Anyway I know what is wrong now - but... the most irritating thing... I don't have any 390Ω resistors in stock !

More later. :D
Click to expand...

Nice start.
Any progress to report?
Any recent or final testing to describe?
Is it time for final words on this?
 
Well, the latest is that I am still considering the main capacitor upgrade, and being forced by component availability of 40mm diameter replacements to go for capacitors that I wouldn't normally choose, the upside of this is the simplicity of replacement. What this does is to make me look harder at the possibilities for using 50mm diameter main capacitor replacements, I was thinking about buying 4 50mm clamps just to see how possible it is to fit them in. I have even drawn it out as accurately as I can, to see where the pinch points are, as you can maybe guess, I want this to 'look' and to 'be' properly done and in no way a kludge.

Just holding off for a while regarding the 2 smaller can capacitors, while I think about the main capacitors.

That's about all for now, another update will follow when I have news.

With thanks to Ron, for keeping me on my toes about this. :D
 
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Well maybe this might help.

I, in my obsessive wont, took the main filter capacitor mounting plate from my donor X1 down to my favorite parts shop here in Osaka.
They stock those big Nichicon KG Gold Tune filter capacitors.

I placed four of the Nichicons on the mounting plate and they all fit.

Double checking with my Vernier gauge, I measured the minimum width of the mounting plate to be 60 mm,
and the maximum width of the Nichicon KG Gold Tune is 50 mm.

So...if you are considering Nichicon KG Gold Tune, its do-able.
Perhaps with a bit of alteration to the mounting plates, but do-able.
 
Ronito6 said:
Well maybe this might help.

I, in my obsessive wont, took the main filter capacitor mounting plate from my donor X1 down to my favorite parts shop here in Osaka.
They stock those big Nichicon KG Gold Tune filter capacitors.

I placed four of the Nichicons on the mounting plate and they all fit.

Double checking with my Vernier gauge, I measured the minimum width of the mounting plate to be 60 mm,
and the maximum width of the Nichicon KG Gold Tune is 50 mm.

So...if you are considering Nichicon KG Gold Tune, its do-able.
Perhaps with a bit of alteration to the mounting plates, but do-able.
Click to expand...

That is really useful - thank you very much Ron.
 
Hyperion said:
I have decided that 40mm main capacitor replacements are the way to go, just too much trouble and expense to go with 50mm, for too little gain.
Click to expand...

Great!

If you could test your old ones when you remove them that woud be appreciated.

Really would like to see how well they've aged.
 
+1 one on Tom's comment earlier to not rule out Cornel Dubilier PS caps. He mentioned them to me a while back and I'm happy with those in a few of the triple digit amps. However, also check United Chemi-Con if you aren't set something else. I've also used +105deg, 40mm, 10,000uF caps from United Chemi-Con in my 777 variants for a while now and am extremely happy with build and performance... if I recall it is the KMH series with low ESR. Not as shiny as nichicon for sure, but the subtle colouring IMO does look more industrial/serious and vintage.

Cheers
David
 
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Hyperion said:
And now for a progress report.

As I previously mentioned, I was unable to set right channel bias, and while making measurements to compare the channels I did something to the left channel which caused the same effect. I am happy to report that I have restored the ability to set bias on the left channel, (shorted TR16 replaced) and begun working on the right channel this morning.

Here is a picture of the right channel heatsink, showing the right channel OP transistors only.
View attachment 717120

And a picture of the right channel driver board - completely untouched by me. (apart from desoldering various connections to be able to remove the module).

View attachment 717121

Having taken as many voltage and resistance measurements as I could with the module in situ, I set about finding out what was wrong - expecting as with the left channel a shorted or open transistor. Knowing I could set DC offset ruled out the input FET and nine other transistors, leaving 7 to look at, I went through them all checking with my multimeter on 'diode test' and found nothing definitely wrong, but a few weird readings made me remove several to double check with my Peak Tester - all seemed good. I checked that the bias trimmer actually adjusts, and checked all diodes - all good. I checked the emitter resistors of TR10/11, TR15/16 and TR13/14, all good - and began wondering if I had some nightmare fault, like an intermittent transistor or something.

Then my eyes fell upon R36 and R37, they have the look of 'fuse resistors' (although they aren't) but otherwise look innocent enough, 390Ω - so I checked them, one measured 211KΩ and the other one was open :yikes: - take a look below - the base stoppers for the driver transistors both effectively open!

View attachment 717124

I am left scratching my chin as to 'how' these came to be like that - needless to say I'll be checking the other channel as well. I learnt a lot finding these faults, I now have some extra tricks up my sleeve when troubleshooting similar amplifiers. ;)

Anyway I know what is wrong now - but... the most irritating thing... I don't have any 390Ω resistors in stock !

More later. :D
Click to expand...

Just the thread I was looking for regarding R36 & R37 !! ... and I'm happy it's you @Hyperion because you definitely know what you are doing.

A couple of days ago, R37 blew on the left channel of my X1 when I touched TP01 on the left MM board (I have no idea why that would have caused the resistor to blow). It's seems like touching TO1 somehow shorted the left channel. I heard a pop on the left speaker and saw the magic smoke come up from the left F-2775 amp driver. I remembered that @Ronito6 had alerted us about R36 & R37 resistors so that's why I checked those first. Sure enough it was R37 that had blown open.

The problem happened not long after I soldered the two resistors together on R43 of the MC PS F-2778 but I can't see how it's related unless I loosened a wire or something when I opened the front of the amp to re-soldered R43. Either way, all voltages were stable afterwards and it was playing beautifully. It continued playing fine after that until so I didn't give it any thought until the mishap.

What do you suspect caused the issue in the first place? I don't think that should have happened when touching a test point.

Since you had a similar issue with those resistors, what components would you advise I check on F-2775?

Any troubleshooting tips would be appreciated. Thanks!

*I don't want to divert this thread but for some reason I was unable to PM you.
 
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