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Old 18th September 2011, 01:59 PM   #1
Jens A. is offline Jens A.  Denmark
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Default GK-1: Right channel dead

A couple of months ago I got a new shelving system for both my audio system and a few other things. In that connection my GK-1R was taken temporarily out of commission.

After making appropriate holes in the shelving system for cabling, the GK-1R was installed into the system again - but now the right channel was dead!

After making sure that it was not a cabling problem (which is was not), I took the GK-1R out and - being virtually electronically illiterate myself - contacted Hugh.

After a few measurements, we found out that it looked as if either T4, a BC557, and/or the LED was failing.

I have now replaced both T4 and the LED, but the right channel is still dead

I have just written to Hugh a few hours ago and am awaiting his deliberations - but it occurred to me that an error like this (whatever it is) could happen to other GK-1 owners and might be of interest, hence this post.

I should stress that Hugh has been very helpful indeed in the matter, whereas I have been somewhat slow in getting and installing the replacement components (due to summer vacation and a swamped cellar ...).

I shall post again once Hugh and I have had a gander about what to do next

Cheers,

Jens
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Old 18th September 2011, 02:23 PM   #2
AKSA is offline AKSA  Australia
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Jens,

Usually when something fails after a spell in storage it's a connection issue.

Try removing all the plugs, sockets, tubes and refitting them. This is first base only, of course.

Next, measure the voltages on the SS power supply - should be +/-14-15V - and on the tube anodes you should have 135-145V all round.

If these check out we go further into the circuit to isolate the issue.

Apologies for not answering you today, it was a beautiful spring day and I took a few hours off!

Cheers,

Hugh
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Old 18th September 2011, 02:32 PM   #3
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Jens,
While you have your GK-1 apart, be sure to remove R2, the 10R resistor in the ground track, and replace it with a wire link. This should remove any residual hum that exists.
Gk-1's can sometimes seem to have a mind of their own. I once took mine down to Hugh's to demo a modification I had done, and when I got there, one channel was dead. It took us a couple hours to bring it back to life. I think the air in the train must have been bad for the Gk-1, although it was okay for me.

Steve
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Old 18th September 2011, 08:14 PM   #4
Jens A. is offline Jens A.  Denmark
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Originally Posted by AKSA View Post
Jens,

Usually when something fails after a spell in storage it's a connection issue.

Try removing all the plugs, sockets, tubes and refitting them. This is first base only, of course.

Next, measure the voltages on the SS power supply - should be +/-14-15V - and on the tube anodes you should have 135-145V all round.

If these check out we go further into the circuit to isolate the issue.

Apologies for not answering you today, it was a beautiful spring day and I took a few hours off!

Cheers,

Hugh
Hi Hugh,

Already did that when we started discussing this problem a few months ago. The tubes are fine, glowing nicely, and all tranny voltages are fine as well - rechecked that yesterday.

And as we agreed previously, I have replaced T4 and the green LED - still the problem persists.

Please see private email as well ;-)

And this being a Sunday, I certainly did not expect you to reply right away - I sincerely hope you and Sri enjoyed the nice weather!

Cheers,

Jens
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Old 18th September 2011, 08:17 PM   #5
Jens A. is offline Jens A.  Denmark
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Originally Posted by stvnharr View Post
Jens,
While you have your GK-1 apart, be sure to remove R2, the 10R resistor in the ground track, and replace it with a wire link. This should remove any residual hum that exists.
Gk-1's can sometimes seem to have a mind of their own. I once took mine down to Hugh's to demo a modification I had done, and when I got there, one channel was dead. It took us a couple hours to bring it back to life. I think the air in the train must have been bad for the Gk-1, although it was okay for me.

Steve
Sure thing, Steve! Thanks for reminding me. I may have done this a couple of years back, but I will recheck ;-)

I am certain Hugh and I will get my preamp up and running again soon - and it has never been on a train!

Cheers,

Jens
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Old 18th September 2011, 10:56 PM   #6
AKSA is offline AKSA  Australia
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Jens,

If all voltages check out, then it seems to me that the signal is just not getting through. Once DC conditions are met, the amp should amplifier, but only if a signal gets to it.

Accordingly, take the input signal via coax directly to the input on the board, that is, solder up a jockey coax with an RCA on the end.

Now try it..... if signal now gets through, then the problem lies at the input switching level - not the main board.

I'm sorry the CCS replacement did not work.

Cheers,

Hugh
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Old 19th September 2011, 06:56 AM   #7
Jens A. is offline Jens A.  Denmark
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Quote:
Originally Posted by AKSA View Post
Jens,

If all voltages check out, then it seems to me that the signal is just not getting through. Once DC conditions are met, the amp should amplifier, but only if a signal gets to it.

Accordingly, take the input signal via coax directly to the input on the board, that is, solder up a jockey coax with an RCA on the end.

Now try it..... if signal now gets through, then the problem lies at the input switching level - not the main board.

I'm sorry the CCS replacement did not work.

Cheers,

Hugh
Hi Hugh,

It is not a signal problem.

The green LED does not light up, and voltage accross it is only approx. 1 V, as I described in my email to you.

Left side LED is shining brightly as it should, approx. 1.8-1.9 V accross it.

I'm thinking it could be something in the power supply?

Cheers,

Jens
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Old 19th September 2011, 09:14 AM   #8
AKSA is offline AKSA  Australia
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Jens,

Ah, OK.

What are the voltages on the two power rails, one positive, the other negative, for the SS section? That implies that there are only a couple of volts available, as the LED is not lighting up.

This in turn points to the emitter follower which supplies the positive rail with power.

Jens, I will email you.

Cheers,

Hugh
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Old 19th September 2011, 09:59 PM   #9
Jens A. is offline Jens A.  Denmark
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Join Date: Dec 2009
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Originally Posted by AKSA View Post
Jens,

Ah, OK.

What are the voltages on the two power rails, one positive, the other negative, for the SS section? That implies that there are only a couple of volts available, as the LED is not lighting up.

This in turn points to the emitter follower which supplies the positive rail with power.

Jens, I will email you.

Cheers,

Hugh
Hi Hugh,

Not quite sure where to measure the "power rails", however have made the measurements you asked for and emailed those to you.

This is getting interesting ...

Cheers,

Jens
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Old 19th September 2011, 10:10 PM   #10
Jens A. is offline Jens A.  Denmark
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Originally Posted by Jens A. View Post
Sure thing, Steve! Thanks for reminding me. I may have done this a couple of years back, but I will recheck ;-)

I am certain Hugh and I will get my preamp up and running again soon - and it has never been on a train!

Cheers,

Jens
It turns out that I did not remove the R2s. However, since this is a GK-1R (the remote controlled version), I may have done something on the Relay Board. I still think it is a good idea to remove the R2s, so I'll try it out!

Cheers,

Jens
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