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G-22000 - protection circuit time delay problem

w1jim

w1jim

I can fix it but good...
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G-22000 - protection circuit time delay problem & recapping adventure

Oh, I love this vintage stuff, it sounds great and never fails to keep me on my toes.

Normally when powering up my G22k it takes about 10 seconds before the red protection LED goes out and the green goes on.
But the other day the delay was basically non-existent and the speakers made a semi-nasty sound on power up.
After that - all was sweetness as usual.
In my research I found an earlier thread that address this issue and the recommendation was to clean the auxiliary power switch that is on the rear panel (on the amp section adjacent to the fan outlet). I tried cycling it a few dozen times to clean off any crap (at least until I could get in there with some DeOxit) but that didn't change the no-delay behavior.
I've been turning off the speaker switches prior to power on when using it in this state as a temporary safety measure.
I've already recapped the front half of this unit so I figured it's time to recapped the back half - the power supply, protection and amp PCBs. I placed the order with Mouser for the various higher voltage caps required.

But behold - this evening I turned it on and it went through the normal 10 second delay. Now, I'm nowhere religious enough to think that this has fixed itself so I'll be going forward with the recapping and servicing exercise.
Where previously I suspected either the aforementioned power switch or the transistor (SCR?) that drives the relay now I'm thinking that the relay itself was mechanically locked up. It's possible that the contacts were arced together from the power being rapidly cycled and now it's broken loose again.

Any thoughts?

JimB
 
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Interested to see the outcome of this...

Not to de-rail the thread or anything but are you going to do a thread similar to your G-9000 when you recap?
 
Clean the power switch on the amp section. If that don't work, you have a fault in the protection circuit and it will likely need a rebuild.
 
The G-22/33 have extremely complex protection circuits. There's a section in the service manual that discusses it's operation. If memory serves, it monitors 5 different operation factors to decide if it's safe to power the speakers. It would be pretty lucky if someone has had your exact symptoms and know the cause because it's going to be a bitch to troubleshoot in the few seconds the system operates.

- Pete
 
Well, if I had a middle name then it would be "Lucky". For now it'll have to be my nickname because now the protection circuit is working properly with no intervention from me. But just because it's working doesn't mean I can't fix it!
The Mouser truck showed up today with some parts so I'll be getting into this pretty soon. I'll be recapping the amp/PS chassis and perhaps the tuner section. I've already done the preamp and tone boards.
Of course I'll spray some more DeOxit in there once I open 'er up.
I'll be paying particular attention to the protection relay contacts and for PCB cracks. I'm sure something will show up that's questionable.

Now I just have to get up the energy to unbolt the 2 halfs and bring it downstairs to the shop.
 
Well - here we go.
I pulled the G-22000 out of the mancave system today, unbolted the halves and got to work on the (rear) amp section.


First step - recapping the 2 amp boards. Straight forward - the 2 boards unplug from the chassis and each have a single signal cable that plugs in on the upper edge.
There were also 2 1uf/50v caps on the underside of the board that parallel some diodes.

F2900 (left channel)
F2901 (right channel)
Number of parts listed are for the 2 boards
  • 4 - 220uf/100v
  • 2 - 100uf/50v
  • 2 - 100/16v
  • 6 - 1uf/50v - one on each board (2 total) replaced with a poly film cap - the white rectangle on the right board.

PCB on left is stock - right one is recapped.


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On to the 2 power supply boards.
I've completed the right board and found one solder joint at a capacitor that was cracked to the point of being disconnected. Satisfying to know I'm actually fixing something.

F2903 - Right power supply
  • 2 - 470uf/120v
  • 4 - 100uf/100v
  • 2 - 3.3uf/100v
  • 2 - 100uf/35v
  • 2 - 100uf/25v
  • 1 - 100uf/6.3v
  • 1 - 470uf/10
  • 1 - 1uf/50v

F2902 - Left power supply
  • 2 - 470uf/120v
  • 4 - 100uf/100v
  • 2 - 3.3uf/100v
  • 2 - 100uf/35v
  • 1 - 100uf/6.3v
  • 1 - 200uf/50v
  • 1 - 47uf/50v


Board on left has been recapped, right one is awaiting it's fate tomorrow.

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Nice work Jim, we are getting a very nice tour of the inner workings and indeed your good work on these amps, great to see.
Thanks for sharing the documentation too, very valuable indeed.....
 
Those pictures give you a really good impression of the reduced size of modern replacement electrolytic capacitors. I think it must improve performance somewhat just allowing those PCB mounted heatsinks, and everything else around to 'breathe' a bit better.

Thank you for the in depth look - interesting and instructive.
 
As has been mentioned in other such threads it is almost disconcerting how small modern replacement capacitors are. On the power supply boards the large caps are originally rated for 120 volts - the replacements (slightly smaller) are rated at 160 volts. Most of the other replacement caps have been similarly replaced with higher voltage parts. This decision is largely based on availability.

Although hard to see, on one of the power supply board there is a 3.3uf/100v cap that was located adjacent to one of the large (hot) power resistors - I left the leads on the replacement about 3/4" long, covered them with teflon sleeving and positioned it away from the heat.

Today I'll be examining the contacts on the 2 center mounted relays for the protection circuitry. Initial examinations make me think they might just get a simple burnishing.
 
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Weekend update - I cleaned the power relay contacts, which looked like they had normal wear and also replaced the DC offset and bias pots on the 2 amplifier PCBs with Bourns 25 turn parts - makes the adjustments much easier and allowed me to adjust them both right to spec (0 mv +/- 3 for the offset and 15 mv +/- 5 for the bias).
Put it all back together and after a few anxious minutes with the pre/main switch in the wrong position everything is working fine.

I opened up the front - tuner/preamp section and have started recapping the tuner section. Most of the other boards were done last year.
Stay tooned...
 
Tuner time!

I noticed that some caps differed from the schematic, so YMMV.

F2920 Tuner PCB
  • 10- 10uf/16v
  • 2 - 220/16v
  • 3 - 47uf/16v
  • 1 - 220uf/6.3v
  • 3 - 1uf/50v Low Leakage
  • 2 - 10uf/25v Low Leakage
  • 2 - 2.2uf/50v Low Leakage
  • 3 - 0.47uf/50v Low Leakage - replace w/poly film
  • 1 - 1.0uf/50v BiPolar - replace w/poly film
  • 1 - 10uf/16v BiPolar
  • 3 - 1uf/50v Replace w/poly film
  • 1 - 47uf/6.3v
  • 1 - 4.7uf/25v BiPolar
  • 2 - 3.3uf/50v
  • 1 - 4.7uf/25v
  • 1 - 3.3uf/35v Tantalum - replace w/electrolytic
  • 1 - 1.0uf/35v Tantalum - replace w/poly film
  • 1 - 0.22uf/35v Tanatlum - replace w/poly film




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Here are 2 pictures for future reference of the underside of the G-22000.

In the first picture you can see board F2906 where I replaced the 2 - 1.0uf/50v BiPolar electrolytics with WIMA 100v poly film caps (circled). These are the caps that go inline when the capacitor coupled position is selected on the pre/main switch (on the side).

Most of these boards were recapped by me last year - witness the green and gold Nichicon caps and the white poly film caps mounted on the bottom of the phono PCBs to the right in the first picture.

I'll be addressing the power supply board that's buried in there - notably the protection circuit and some caps that are mounted adjacent to the heatsinks.



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As always Jim, nice work going on there.....nice clear pictures too......
I will need all this when I get my giant G some day.....
 
More fun - today I recapped the tuner/preamp power supply. I repositioned 3 caps (circled) a little bit so as to get them away from some resistors which may get hot (judging by the condition of the ones I pulled).
Some of the caps (like the 1000uf caps) were replaced with higher voltage parts since that's what I had on hand.

F2893 Power Supply Circuit Board
  • 3 - 1000uf/50v
  • 3 - 470uf/50v
  • 2 - 100uf/35v
  • 1 - 220uf/35v
  • 1 - 220uf/50v
  • 3 - 100uf/10v
  • 1 - 100uf/16v
  • 2 - 1uf/50v
  • 2 - 2.2uf/50v
  • 1 - 3.3uf/50v


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There are some PCBs that I recapped last year and I do not have the parts lists for. I've summarized the ones I could easily identify without any disassembly below:

F2906 - Pre/Main PCB (mentioned in a previous posting)
  • 2 - 1uf/50v - replaced with a WIMA 100v poly film cap

F2893 - Connector PCB
  • 1 - 10uf/16v

F2880 - EQ Circuit Board - there are 2 of these, I've listed the count for both boards below
  • 2 - 22uf/50v BiPolar
  • 2 - 1uf/50v - replaced with a poly film

F2884 - EQ Mother Board
  • 2 - 470uf/35v

F2899 - Tone Flat Amp - there are 2 of these, I've listed the count for both boards below
  • 4 - 100uf/35v - these are wired back to back to simulate a BiPolar - I'd suggest replacing these with a single 47uf/35v BiPolar
  • 2 - 1uf/50v - these are mounted on the rear of the board and may have been a later upgrade - replace with poly film caps

F2890 - Tone Amp
  • 2 - 22uf/25v BiPolar
  • 2 - 47uf/25v BiPolar
  • 2 - 4.7uf/35v BiPolar

F2884 - Selector Board
  • 2 - 470uf/35v

F2888 EQ Mother Board
  • 2 - 470/35v
  • 1 - 220uf/35v BiPolar - I didn't notice this in the schematic and it's mounted of the edge of the board; this may have been a later upgrade

F2892 - Peak Meter Board
  • 2 - 220uf/10v
  • 4 - 10uf/25v
  • 1 - 4.7uf/50v
  • 1 - 100uf/6.3v
  • 2 - 4.7uf/50v
  • 1 - 100uf/16v
  • 1 - 3.3uf/50v
  • 1 - 3.3uf/50v - Low Leakage
  • 1 - 4.7uf/50v - Low Leakage
  • 2 - 2.2uf/50v - Low Leakage

The following boards I don't have data for at this time:
F2886 - Volume Control Board
F2885 - Microphone Amp Board
 
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Frankly, I generally don't bother removing most of the glue. I don't think it bothers anything and the more I scrape around in there the more likely I'll screw something up. I can do that on my own without any extra help.

I've gotten the big "G" in the living-room with the SX-1980 - stay tuned for the big dawg face-off :banana:!
 
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