CR-1000 power off thump

39cross

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Finally at long last I have finished the recapping, re-lamping and 2SC458 transistor replacements, including all electolytic caps including the 2 big 10,000uf caps, as well as all the tantalum caps. I put it back inside the case and brought it up to the kitchen system, which consists of a pair of ADS LS-520's, TD-146 w/ DL-100 cart, and Marantz 5003 cd player.

Word is: I am truly amazed at how good this receiver sounds. The sound is exceptionally clean on all inputs, but I am especially impressed at how good the phono input sounds. There is an exceptional clarity I have not experienced before. Maybe it's the Natural Sound. I could play LP's all day and not get tired of listening. I'm not sure how best to describe it, but there is a transparency to the sound I have never heard before and it is intoxicating. It makes every record sound more alive.

However, there's one last issue, and that's a speaker thump at power off. It wasn't as bothersome with the Rectilinear HighBoys I had them hooked up to in the workshop. But with the ADS's it's pretty much in your face.

What should I look for here? The DC Offset etc. have all been set. From what I've been able to research thus far it seems the relay is not getting engaged in time when the AC shuts off? Maybe some transistor needs replacement? I would sure like to fix this, then it will be perfect.
 
If your DC offset is at zero or very close it should not happen. Yamaha in most units grounds the back contacts of the protection relay. Thus if there is any residual DC on the outputs it will get shunted to ground an you wll hear a pop.
 
Finally at long last I have finished the recapping, re-lamping and 2SC458 transistor replacements, including all electolytic caps including the 2 big 10,000uf caps, as well as all the tantalum caps. I put it back inside the case and brought it up to the kitchen system, which consists of a pair of ADS LS-520's, TD-146 w/ DL-100 cart, and Marantz 5003 cd player.

Word is: I am truly amazed at how good this receiver sounds. The sound is exceptionally clean on all inputs, but I am especially impressed at how good the phono input sounds. There is an exceptional clarity I have not experienced before. Maybe it's the Natural Sound. I could play LP's all day and not get tired of listening. I'm not sure how best to describe it, but there is a transparency to the sound I have never heard before and it is intoxicating. It makes every record sound more alive.

However, there's one last issue, and that's a speaker thump at power off. It wasn't as bothersome with the Rectilinear HighBoys I had them hooked up to in the workshop. But with the ADS's it's pretty much in your face.

What should I look for here? The DC Offset etc. have all been set. From what I've been able to research thus far it seems the relay is not getting engaged in time when the AC shuts off? Maybe some transistor needs replacement? I would sure like to fix this, then it will be perfect.

Do you have a " power up" delay before the relay "clicks" ?
 
Do you have a " power up" delay before the relay "clicks" ?
Yes, on power-up there is a several second delay then the relay clicks followed immediately by sound (and no thump). On power-off, the relay clicks immediately.

I hauled the receiver back into the workshop and re-checked all of the settings. I had set and reset all of these several times before putting it into service in the kitchen and they had seemed stable. However, the left side main amp board was out of spec for the 1st adjustment item (primary stage diff. amp circuit), it had drifted to 15.5v, out of spec of 15.0v +/-.15. Idling current and mid-point voltage were in spec.

The right side amp board primary stage diff. amp circuit and idling current measurements were in spec, but the mid-point voltage had drifted a lot, maybe 0.090v instead of 0.0v. I see this measurement point is connected to the relay on the main power board. I reset both but they are not keeping stable values. What would cause this, are the trimpots the problem?
 
Midpoint--DC offset will drift up and down depending on the ambient temp within the amplifier.Replacing the adjustment trimmer my help minimize the drifting.
 
Midpoint--DC offset will drift up and down depending on the ambient temp within the amplifier.Replacing the adjustment trimmer my help minimize the drifting.

Thanks Dave - yes it drifts up as the temp goes up, for sure. Idling current too but it stablizes. For now, should I leave it on and then adjust to the typical period I run it, 1 hour+?

Also, do you have a Mouser (or other) part number you might recommend? I haven't reached this stage in repair yet.
 
Thanks Dave - yes it drifts up as the temp goes up, for sure. Idling current too but it stablizes. For now, should I leave it on and then adjust to the typical period I run it, 1 hour+?

Also, do you have a Mouser (or other) part number you might recommend? I haven't reached this stage in repair yet.

These 5k trimmers are single turn. Singlr turns are easiest to center versus multiturn. I like using single turn in the DC offset,midpoint,DC balance,balance
position. Multiturns in the bias/idle position.
VR601 DC offset
http://www.mouser.com/ProductDetail...=sGAEpiMZZMvygUB3GLcD7rufck0TIBKyNmTMsByE0RA=
 
trimmers replaced

Got the trimmers yesterday and replaced them all. I used the part you spec'd for VR601, and multiturns for VR602 and VR603. The DC offset is still drifting, but not as bad and seems to stabilize out OK although it is slightly out of spec. The other measurements stay within spec.

This is what I measured for DC offset, after fiddling with it for a bit:

1 minute -> -0.020
2 minutes -> -0.007
3 minutes -> 0.000
5 minutes -> 0.009
10 minutes -> 0.013
30 minutes -> 0.018
45 minutes -> 0.021
60 minutes -> 0.021

The spec is 0V +/- 0.01. It changes quite a bit over the first 10 minutes but after a half hour seems to stabilize.

I don't seem to be getting the power off thump now. Are these numbers OK? Or should I be looking at replacing other parts? Should I try swapping the output transistors between boards and see if the problem follows them?
 
DC Offset finally fixed!

It turns out the numbers I had above were not correct - it must have been because the receiver was already warm. Starting from absolutely cold the numbers were much worse and I could not get rid of the pop in the right channel.

But this has a happy ending, and I think I earned my first merit badge.

So this is how it went down. I may have reached the right answer through faulty reasoning and luck since I really don't understand circuits. First I did some research on DC offset and problems therewith. To make a long story short, from this I concluded that the problem would be with a pair of transistors on the main amp board. It looked like TR602 and TR603 might be the responsible pair of transistors. These are 2SA572's. Suggested replacements were KSA992's. I had some on hand and was able to match up a pair of identical hFE values, so these went in as replacements.

Fired it up, adjusted VR601 and the readings are now rock steady and hold at around 0.0V. Decided to do the same replacement on the left channel so I would not have to open this up again, at least for that reason. And now it is done and playing (and shutting off) beautifully. DC measured at the speaker outputs holds steady over time once warmed up at 0.0V +/- 0.002V.

So I hope this will be helpful to any other CR-1000 owners in the same situation.
 
It was a happy ending for the DC offset problem.

Unfortunately I then ran into the next issue with the low filter and bass turnover switches. That's another thread. I'm going to try swapping out the filter amp board and see if that has any effect, just haven't had the time.
 
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