Troubleshooting Suitcase Janus Preamp - no output...

[Seaglass]

Ok all, again I'm new here. The preamp on my '77 suitcase was sort of working but now seems to have died totally. Of course I can still get output from the harp or the accessory 1 jack. Before it went it would occasionally have really low output (like 5%) at full volume. Checking inside the preamp the caps seem to be pretty old. The main power lamp will still light but the vibrato no longer will (it was working fine). I figure that new caps are the place to start but I didn't know if there are any other known problem areas there. Thanks!

[pianotuner steveo]

The very first thing I would try is to resolder (reflow the solder) on the PC board(s) and see if that helps. Also try cleaning the controls.

[Seaglass]

I've never really worked on a circuit board this old. Would I stick the whole thing in an oven to reflow it?

[pianotuner steveo]

No..... I would never attempt that. That could completely dry out the caps and worse.  Assuming that you know how to solder, you basically disconnect from power, remove the PC board, then re heat the solder on all connections with the soldering iron. Be careful not to accidentally flow solder onto neighboring connections, therefore possibly causing shorts. Also, you may find corrosion on the board. Carefully clean off with a small brush and some contact cleaner, I recommend wearing safety glasses ( due to a bad experience I once had) when working with contact cleaner.

Always try simple things like these before spending money on parts. Sometimes bad connections and dirty controls are the only problems.

I also recommend taking pictures of the board(s) before you start in case any wires break off, so that you know where they go.

[The Real MC]

I've never really worked on a circuit board this old. Would I stick the whole thing in an oven to reflow it?

If there is any indicator that your problem should be better left in the hands of a qualified expert, this is it.  Just by this question alone shows that you have no idea what you are doing.

[Seaglass]

i was pretty sure that's what you meant but on the SMC parts I've worked on re flowing means something different. Thanks.

[Alan Lenhoff]

If you search the group's archives you'll find several threads about a common problem on the Janus amps.  Quoting former Rhodes designer Steve Woodyard:

"The most common power amp failure (on the Janus amps) was related to connections between the PCB and the harnesses. The male connectors that soldered into the PCB had frequent cold solder joints. Re-solder all connectors."

The plastic connectors on the boards seem to be held in place by nothing other than solder, and often break loose. That might be a first place to look as you reflow joints.  Fixing that solved a problem on my Suitcase amp. I also took the suggestion of other list members and used some hot glue to adhere the plastic connectors to the board, which may help prevent a recurrence.

http://ep-forum.com/smf/index.php?topic=8450.msg44725#msg44725

Alan

[JanneI]

I just resoldered the pots of an old peterson preamp, now works like a charm! Cold solder joints is the first suspect, try it before you go changing the components. It is the easiest fix, particularly if you don't know much about electronics.

[Seaglass]

Thanks again everyone, as soon as I get a chance I will reflow the preamp and see if that helps. Given the intermittent nature of the failure prior to it dying completely that sounds like a very probable culprit. The actual amp itself seems to be working fine - if I take a signal into the return from the amp effects loop both sides are working well so I hope the whole problem is in the preamp. The vibrato light had been lighting up and now is not so that also makes me think the problem is there.

I had seen that about the stress on connectors and when I get a chance to open up the amp itself I will drop some hot glue on there to beef up the connection.

[Max Brink]

Quote from: Seaglass on September 06, 2015, 06:19:44 AM
I've never really worked on a circuit board this old. Would I stick the whole thing in an oven to reflow it?

If there is any indicator that your problem should be better left in the hands of a qualified expert, this is it.  Just by this question alone shows that you have no idea what you are doing.

--Try a George Forman! 


If you do not know how to repair the solder connections in an XLR cable or on a circuit board like the Janus then I am 100% with The Real MC that you should leave this to someone more qualified. But here is some advice to help re-focus your efforts rather than firing-from-the-hip reflowing connections that might be perfectly good...


First, let's determine if your preamp is working fine or it the breakdown is in the power amplifier. (Or it could always be experiencing problems in both). Try the preamp outputs on the suitcase through an external amplifier. Do they pass signal at a normal volume and does the vibrato work even though the LED is not indicating?


The plastic connectors on the power amps are indeed the most common failure I see in Rhodes amps. The contacts in the headphone output can also be prone to intermittent failure. But I wouldn't start to look here until we have proper signal through the preamp outputs.

Also, double check your 5 pin cable. open it up to double check the connections inside and also check with a meter to make sure it is passing signal from all points.

The cable test and preamp test are the first two things I would check before taking any action.