Model 600 power up occurence

kylerhea

Member
Hi!

Could someone please help with an advice with my model 600?

I have just recapped my model 600, 4 main caps and all the caps on the power supply board.
Upon initial power up there was the sound of a spark (I did not actually see it) accompanied by slight traces of bright smoke and a light smell.
Initially I wanted to shut it down again but then I recognized the relay clicking within the normal time period and the bias stabilizing at roughly 30mV (a DMM was connected). So I left it switched on for about half an hour on my test bench with some test speakers. I had almost zero DC offset from the beginning and could adjust for quite stable bias on both channels. There was undistorted sound from both channels, too.
Visual inspection of parts did not show any problems yet. All polarities have been checked and double checked before first power up and there are no terminals too close to each other or to chassis ground.

About one hour after that first test I switched it on again and everything powered up normally and remained like that.

Is it possible that this initial frightening phenomenon was caused by the first rushing in of power and loading of all those new caps?
Which power supply parts or voltages should I check before putting it into daily service again?

Thanks to all in advance.

Marc,
Austria
 
Hi!

Could someone please help with an advice with my model 600?

I have just recapped my model 600, 4 main caps and all the caps on the power supply board.
Upon initial power up there was the sound of a spark (I did not actually see it) accompanied by slight traces of bright smoke and a light smell.
Initially I wanted to shut it down again but then I recognized the relay clicking within the normal time period and the bias stabilizing at roughly 30mV (a DMM was connected). So I left it switched on for about half an hour on my test bench with some test speakers. I had almost zero DC offset from the beginning and could adjust for quite stable bias on both channels. There was undistorted sound from both channels, too.
Visual inspection of parts did not show any problems yet. All polarities have been checked and double checked before first power up and there are no terminals too close to each other or to chassis ground.

Checked how? What did you use as a reference?

About one hour after that first test I switched it on again and everything powered up normally and remained like that.

Is it possible that this initial frightening phenomenon was caused by the first rushing in of power and loading of all those new caps?

Only if there is a fault. There wouldn't have been any charge in the original
caps either when the amp was new.

Which power supply parts or voltages should I check before putting it into daily service again?

Thanks to all in advance.

Marc,
Austria

You're going to need to do some more visual inspection. If there was
sparks and smoke, there should be something that can be seen visually.
Unplug the main power supply board and check the contacts in the socket.
Do a close visual inspection both on and around "all" components.
Check for any burn marks on both the PC boards and anywhere on the metal chassis.
Also do a close check of the foil side of the PC boards. The aching could
have been taking place at a bad solder joint. Check the joints closely.
 
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Thanks for your thoughts.

Polarities have been checked with the service manual and are correct.

No fuse had blown, the pilot lamp was working all the time.
I could not find any problems during a visual inspection.

So I am hoping it was a single event spark (possibly from the power switch).

The amp is working for several hours now without any problems.

Bias is fluctuating between 24 and 26 mV at operating temperature.

It is however a little on the high side upon power up, somewhere around 35 mV decreasing slowly afterwards.

Are there any other components (electrolytics are already replaced with Panasonic FC) that should generally be replaced on the removable power supply board?
Is it recommended to replace the bias pots with new ones?
Thanks,

Marc
 
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It is however a little on the high side upon power up, somewhere around 35 mV decreasing slowly afterwards.
Normal.
Are there any other components (electrolytics are already replaced with Panasonic FC) that should generally be replaced on the removable power supply board?
Relay driver trans, and any part that got slimed with the assy. glue.
Is it recommended to replace the bias pots with new ones?
Always a good idea to replace stock offset and bias pots. Single-turn Bourns 3386H do fine here.
 
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