missing channel on a suitcase

[Mark II]

first of all you have to know where to start.
best method to track down the problem is to find the source
there are 3 possibilties:
1. bad preamp (built into the piano section with volume, EQ and tremolo knobs)
2. bad cable
3. bad power amp (built into the loudspeaker cabinet)

Bad power amp:
If you own a later build cabinet (e.g. FR7710) you are pretty lucky.:
Use the external/internal connection possibilities of the main amp modul.
Connect another source (e.g. I-POD, CD player, turn the volume down  :x ) to the power amp input jacks
or use the headphone jack to connect a headphone.



If all speakers/channels are working. Fine. it is not the power amp !
Otherwise ... you know where to zoom

If you own an older cabinet with a panel without external jacks you could do this to check if it is a main amp or pre amp related problem:

Warning:
Be aware that there is the danger of an electrical shock when working inside the cabinet. Even if you have unplugged the cabinet (which you should do at first) some electrical parts (capacitors most likely) may have some power loaded which might cause harm to you. So dont touch any metal contacts on the printed circuit boards.

1. unplug the suitcase piano (light socket)
2. open the cabinet (loudspeaker box)
3: there are 2 RCA cables (cinch connectors) going from the connection panel to the 2 power amps. switch them.
4. bring the cabinet back in playing condition and plug it in.
5. play it.

If the same channel/loudspeakers are bad (hum, dead, etc.) it is a bad main amp. If the other channel is missing, you should check cable and preamp

bad cable:
change it or check if all 4-5 pins on both connectors read 0 ohm or have continuity  (you will need an ohmmeter/ continuity tester).measure the same pins on both jacks, meaning one tip of your measuring device on pin #1 of the preamp jack the other on pin #1of the cabinet jack.

bad preamp:
if its not the cable or the power amp it is the preamp.
Otherwise you can use the preamp output/external amplifiers jacks of the later cabinets and connect the preamp to another amp (mixer or guitar amp or even a recording device) to be sure.



In many cases following this "tracking down method" you will have to measure (voltmeter, oszilloscope), swing a soldering iron and read schematics. If you dont know how to do this ask a tech or someone else skilled to help you.

@James: how about a sticky behaviour for this post ?

[Mark II]

Before I forget, it may or not be related, but another reason a channel might be out on the 5 pin models is:

The internal fuse is blown on one of the channels, visible inside the speaker cabinet with the back grill panel off - near where the speaker cables "plug in" to the power amp.

The channel out jacks may be touching each other inside the amp section.  If someone has replaced these or put on "newer" looking lock rings, they might have twisted the jack and the connections are touching some metal parts and shorting the channel.  Adjust out of the way.

I may add Bjammerz suggestion from another thread,  check it, it's for sure worth a look.

Thanks

Mark II

[Chris Carroll]

Obvious but don't forget

-If all of your proper voltages are present then you have a physical issue --
Check  shorting jacks  use your meter in the ohms or diode scale to check- --- Check multi pin connectors and the back of the boards they are a main source of problems. They all should be reflowed as intermittancy is common on this type of amplifier.

www.vintagevibe.com  we have videos on all of this, very easy and simple to follow  

[Electroharmony]

Thought I'd add for 5pin suitcases...

Don't forget to check the the power transistors located on the heatsink, on the outside of the amp. These can be easy to overlook.  There are two per channel, and connect to the blue 6-pin connector.

I recently kept burning out components on one of my amp boards. It turned out both 2N6254 transistors on the heatsink were shorted, and the root of my trouble.  If you need to replace, it's probably a good idea to use new 120pF capacitors, connected across the base and collector.

[Jay]

Back in 1973 my Suitcase lost a channel. Turns out my turkey friend used a bad 1/4" cable and left the tip inside the jack.  It shorted out the channel which worked when I replaced the jack.

[modorange]

I bet 9 times out of ten it is a bad cable connection. We need someone to show how to re-solder the connections on the cable.

[OleA]

Same problem here, or, mine is in the suitcase amp. It occasionally comes and goes, and I have absolutely no clue what so ever as to what might be causing that. Any idea? Or should I just get the money saved up and have it professionally looked over?

[voltergeist]

A problem that "comes and goes" is usually a cold solder joint (assuming a good cable).  The 100W (5 pin) amps are especially prone to that problem.  If it's a 100W amp, take it apart and inspect the boards and re-solder the joints of the connectors.

[samot.comics]

It worth it indeed!!
I started doing all the checking described on the top of the thread with no success..Then I red about that Fuse...And Thank you, my tremolo was only blocking because of that fuse!

[samot.comics]

Hi,
My suitcase is having a missing channel thoses days...I figured it was the fuse of one of the power amp!
From there I just had to find a new one..I found one! I replaced it with the broken one! It worked again...but after 2 hours of playing it broked again!!! Same amp, same fuse!
Because I'm in France, I must plug my rhodes on 120V, the guy who sold it to me gave (sold) me a transformer that look like the same age as the rhodes...Do you think that the old transformer would cause the fuse being broken all the time? But why what would it be only one of the two amp? I guess the answer would be : my amp is having a short circuit somewhere... Any ideas?

[Ben Bove]

It may be one of your amplifier boards is causing the fuse to blow.

It may require amp repair.  One way to check, would be to switch the PCB boards - unhook the 2 harnesses on each board and swap the top one for the middle one.  If the fuse blows on the other slot, then you know one of the boards needs repair.  If the same fuse blows on the same slot, then it doesn't have to do with the board components.

[blueberryjam]

It may be one of your amplifier boards is causing the fuse to blow.

It may require amp repair.  One way to check, would be to switch the PCB boards - unhook the 2 harnesses on each board and swap the top one for the middle one.  If the fuse blows on the other slot, then you know one of the boards needs repair.  If the same fuse blows on the same slot, then it doesn't have to do with the board components.

hey Ben, I'm having the same issue and the power amp board doesn't seem to be the culprit as I switched the board with another one and the fuse blew again. Any idea what could be the cause in that situation? As far as I understand those fuses are only linked to the power amp boards and the headphone jack?

[Tim Hodges]

Have you tried re-soldering the Molex connector sockets on the boards? They often develop cracks in the solder joints.

[blueberryjam]

Thanks for the suggestion Tim. As it happened with two different right channel modules (one of them new) I guess that's a low probability but I'll have a look.

[Tim W]

The fuse is on the output of the amp, between the power devices and the speakers.

If you have already switched the amp module board, the problem could be with the power output devices (DC offset, thermal runaway, etc.). The power devices (two TO-3 case NPN BJTs per channel) are mounted to the outside of the heat sink underneath black anodized covers.  If you end up having to change them, you will need to also remove the board(s) above the sockets so that you can properly seat and remount the new devices.  Pay attention to the mica insulators and thermal grease. Power devices need not be super well matched on a Janus, but should both come from the same manufacturing lot (part number and date code) so that they are similar in their characteristics. Note that if anything gets changed (board, power devices, etc.) you must properly reset the offset and bias trimmers on the amp cards. 

It is also possible that something is wrong with your speakers or the wiring after the fuse, including the headphone jack.  Could be an intermittent short, too low of an impedance to ground, etc.  Compare the two channels with a meter while moving wires around and see if the meter jumps. Intermittent problems can be very tricky to find and recreate reliably.

Run some tests by switching the 1/4" speaker cables and/or the amp card wiring harnesses (one at a time) if you haven't done so already and see if the OTHER fuse or SAME fuse blows.   If you do your bookkeeping right and keep track of what changes you make, you'll get more information that will help lead you to the source of the problem.

Good luck!  Let us know how it goes.

The other Tim

[blueberryjam]

Thank you other Tim !! That's super helpful. I've been told that the headphone jack is not an original and is not even the right part (it makes  a lot of hiss) but the tech who worked on my suitcase didn't have a replacement jack so he left it as is. So it's high on the list of suspects, I'm going to start the investigation with this!