Author Topic: Missing a channel on a Janus amp, and no power LED  (Read 876 times)

Offline hipgroove

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Missing a channel on a Janus amp, and no power LED
« on: July 28, 2017, 04:14:45 PM »
Hello everyone!

I just found a 1976 (I think) Seventy-Three that's in great shape. After moving it into my studio, I fired it up and the B channel isn't working, nor does the power LED on the piano light up. The piano works, as well as the vibrato, and the vibrato LED lights up properly.

If I plug into the power amp input for B with a bass, I get nothing. I've swapped the speaker leads to the amp and the problem follows channel B, meaning the speakers and speaker connections are fine. I've pulled and reseated every connector on the boards, with no change. There's nothing visibly wrong with the components that I can see, and the fuses are fine. I'm not sure if the LED and B channel are at all related, but it's curious that both don't work.

The previous owner swears that it was working fine before we moved it, and I tend to believe him, because he was the one that pointed out that only two speakers were working when we first turned it on.

Any ideas would be very helpful, thanks!

Offline pianotuner steveo

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #1 on: July 29, 2017, 05:53:29 PM »
It could be an open connection (like a cold solder joint) in the B channel amp, but where exactly is anyone's guess. I would start at the speaker connection and work backwards.

 You will have to diconnect it from power and look carefully at the board. The problem won't be in the preamp or (likely not in the) power supply. If you aren't that familiar with electronics, you may need to take it to a local amp guy.
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Offline Jenzz

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #2 on: July 30, 2017, 02:33:39 PM »
Hi .-)

What about the headphone connector? Are both channels working? If so, check the headphone socket. Remind that this socket is a switching socket which cuts off the speakers when a headphone is plugged. The switches inside the socket are always prone to corrosion, so check These...

Jenzz

Offline Ben Bove

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #3 on: July 31, 2017, 12:07:44 PM »
Yes check the points mentioned above, but just pulling and reseating the harnesses on the amplifier boards will not help.  The most common problem with these amplifiers relates to just that - pulling off the harnesses on the power amp can create cold solder joints.  The pins on the boards are not supported structurally, so moving the harnesses may in fact break the connections.

Search the forums for this topic, but basically you'll need to just heat up a soldering iron, and reflow the solder to the pins where the harnesses connect to them.  This clears up the missing channel 90% of the time and is visually hard to see.
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Offline hipgroove

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #4 on: July 31, 2017, 01:39:53 PM »
Jenzz, you may be on to something. When I plug in the headphones, I only get the left side in the headphones, and nothing through any speakers. However, when I unplug the headphone jack halfway, suddenly the B-channel speakers are active, though the A-channel speakers are not. This makes me think you might be right about the headphone jack. Anything specific to look for there?

And I agree, Ben, but frankly, I'd take it to a pro first. I have no problem rewiring my instruments, but I know nothing about these amps and would prefer not to learn on the one one I have ;-)

Offline Jenzz

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #5 on: July 31, 2017, 02:14:00 PM »
Btw, did you check the two 4A fuses located near the speaker connectors on the amp chassis?

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Offline hipgroove

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #6 on: August 03, 2017, 11:39:54 AM »
Btw, did you check the two 4A fuses located near the speaker connectors on the amp chassis?

Jenzz

Yes, they're fine. I inspected the headphone jack and can see nothing obviously amiss. How do these generally fail?

Offline Ben Bove

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #7 on: August 03, 2017, 05:23:01 PM »
Wanted to confirm - is the piano a 1976, with a 3-knob preamp, or is it the Janus model amplifier with EQ-sliders for bass and treble?  Only because they didn't make Janus models in 1976, and wanted to make sure we're talking about the 5-pin amplifier models with the black grill cloth.

If it is a Janus amp, I can almost guarantee it's cold solder joints in your amp boards.  You can sometimes redirect the audio to the other ear as you're plugging in the headphones - the one working amp channel connects to the 2nd contact on the male headphone jack.  If when the headphones are securely plugged in, you only get one channel, and the headphone jack appears to look attached correctly from the amplifier side, then it's not the headphones.

If you're not interested in servicing the amp, you can take it to a local electronics repair tech and ask him to reflow the solder on the pins where the harnesses connect, and hopefully that will fix the problem.  The Janus amps are built like tanks, and things can fail causing a channel to drop but many times it's just bad connections.

There's another test that sometimes works, if you have your headphones on and vibrato going, give the power amplifier a good whack with your hand, right around the center of the unit.  What this does is jars the amp board temporarily, and you might hear contact being made for that short second.  You can't harm the unit, you'd hurt your hand first!  If audio comes in for that split second, its because contacts are not being securely made.  Doesn't always work but worth a shot
« Last Edit: August 03, 2017, 05:31:50 PM by Ben Bove »
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Offline hipgroove

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Re: Missing a channel on a Janus amp, and no power LED
« Reply #8 on: August 05, 2017, 08:58:22 AM »
Wanted to confirm - is the piano a 1976, with a 3-knob preamp, or is it the Janus model amplifier with EQ-sliders for bass and treble?  Only because they didn't make Janus models in 1976, and wanted to make sure we're talking about the 5-pin amplifier models with the black grill cloth.

Yes, its a Janus with the sliders, it must be a later model.

Quote
If it is a Janus amp, I can almost guarantee it's cold solder joints in your amp boards.  You can sometimes redirect the audio to the other ear as you're plugging in the headphones - the one working amp channel connects to the 2nd contact on the male headphone jack.  If when the headphones are securely plugged in, you only get one channel, and the headphone jack appears to look attached correctly from the amplifier side, then it's not the headphones.

So that's the odd part. It's not in the headphones that the right side has audio when the headphones are plugged in halfway -- the B channel speakers in the cabinet start working. Everything looks fine with the jack and the amp internals.

Quote
If you're not interested in servicing the amp, you can take it to a local electronics repair tech and ask him to reflow the solder on the pins where the harnesses connect, and hopefully that will fix the problem.  The Janus amps are built like tanks, and things can fail causing a channel to drop but many times it's just bad connections.

There's another test that sometimes works, if you have your headphones on and vibrato going, give the power amplifier a good whack with your hand, right around the center of the unit.  What this does is jars the amp board temporarily, and you might hear contact being made for that short second.  You can't harm the unit, you'd hurt your hand first!  If audio comes in for that split second, its because contacts are not being securely made.  Doesn't always work but worth a shot

I'm probably going to have to take it somewhere. I'm not afraid of soldering anything, but I am a bit concerned that if this isn't the problem I'll have made it worse.