Paramount left channel goes in and out

[ike]

I am scratching my head here... the left side of the Paramount goes out sometimes, sometimes for a split second and other times for much longer period and when it goes out there is a "thump" to the channel.  Here is another weird thing: when it is out, I would turn off the channel and turn it back on within a couple of second and sometimes it would revive the signal.  I have tried swapping tubes and I looked underneath to see if there is any loose connection.  All the LED's are on and it is not the tubes... Just not sure where I should start to troubleshoot this.

Thank you for any help.

ike

[Paul Joppa]

This may seem a little strange, but what is your power line voltage?

[ike]

Paul,
Sorry to sound like a novice, but I am not sure how to check that...
thanks

[shelby1420]

Paul,
Sorry to sound like a novice, but I am not sure how to check that...
thanks

Smart to ask questions, specially about this one..........  measuring the voltage coming from your wall outlet, could be nasty if you test it improperly...........

[Paul Joppa]

Voltmeter set on AC voltage. If the probes are suitably small you can stick them (carefully!) into the outlet. Don't touch the metal parts!!  :^)

US outlets run around 120 volts these days, but see what yours is. If it's high then there can be excess heat inside the amp.

Guess I should also ask about ventilation of the amp where it's located normally.

[ike]

Both amps are connected to an APC-S15 power conditioner... I just checked the voltage, it's around 123.5V.  The amps sit on an open shelf with a 12 inches clearance between the shelf above, the amps are less than an inch apart from each other.
thank you

[Steve_in_NV]

I kind of had a similar problem had a thump and no audio.  My problem was the Q2 MJE350 transistor on the C4S board but the HLMP 6000 led was off when this happened you indicated you led's never went out.  Mine was intermittent I just happened to see the led's off.  I replaced my transistors with MJE5731A and have never had the problem again.  May or may not be your problem. If you do change them out they have a different pinout. Paul posted here somewhere indicating that.

[Steve_in_NV]

I reckon a cold solder joint could cause strange problems too.

[ike]

Last night I fired up the amps for a listen... half an hour into a blissful listening session, POP!  The left channel goes out, like I have witnessed before.  This time around, I peeked under the chassis and found 3 of the LED lights on the board were out and the LED on the driver tube is out as well.  I presume a cold solder joint is most likely the reason.  Question: Where should I direct my soldering iron to?

thank you in advance

[Paul Joppa]

With three of the four lights out on the board, I would say that the C4S feeding the shunt reg (the on with the smaller MJE-350) has ceased to deliver the goods. Could be a bad solder joint at the transistor, or between the transistor and the rest of the circuit - or it could be a bad transistor. Since your line voltage is a bit high, the latter is a possibility - that's why I asked, and asked about the cooling too. When you are in there, look for burn marks on the PC board!

[Doc B.]

Quick follow up - I am sending Ike a new shunt regulator/C4S board, with an MJE5731A replacing the original MJE350. It appears that in cases of higher than normal AC mains voltage the MJE350 can become stressed over many months of use. The MJE531A is a bit more robust at overly high mains voltage, and we have incorporated it into the new soft start Paramount.

[ike]

Thank you Doc! 

[ike]

Finally, it works!  I have music thanks John.