Author Topic: Dead Channel: Fuses?  (Read 3687 times)

Offline Benjamin

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Dead Channel: Fuses?
« on: April 23, 2007, 05:42:30 PM »
Hi guys,

    Wonderful forum! I have a general tech question about an 88-key suitcase Rhodes with what seems to be a dead channel. The model number is FR7710 on the suitcase (and the top has the horizontal sliders for treble/bass, knobs for vibrato control, etc.).
   
    First, initial problem was a strange sounding vibrato. Investigated and found my right speaker not working (whether vibrato is on or not); right front speaker, facing my knees. Strange sound was apparently just "on-off" instead of left-right. Haven't checked speakers on other side of cabinet.

     Second, tried to narrow down the problem area (I'm not a tech, I should say at this point). 1.) Stereo headphone jack on suitcase works, but only left channel. 2.) Preamp output on suitcase, both channels, work fine. Further, vibrato works fine when recording direct from both preamp channels (i.e. swings from left to right as expected). 3.) Tried out the "power amp inputs" by plugging in a separate sound source via 1/4inch...Channel A, nothing...Channel B, works fine. CONCLUSION; dead channel in the power amp?

    I've read some horror stories about people touching capacitors in these forums and though I can solder fairly well, I'm a little skittish about opening it up.
    Any thoughts would be helpful, r.e. is my conclusion correct? Could it be something else?
    Does this sound like an expensive repair job, or an especially tech-heavy one?

Most importantly, thanks for a wonderful forum. I've owned Rhodes pianos twice in my life and would have killed to have access to such great info and community back then.
   
Thanks,

Ben

EDIT: Finally found this http://ep-forum.com/smf/index.php?topic=594&highlight=channel+power+amp
-sounds identical, only other channel. So, obviously, I'd love to just change a fuse and be back in business. And I'll change my question: Any danger in unscrewing the power amp, looking for a fuse, changing it (if needed), and not touching anything menacing-looking in the process?

Offline pianotuner steveo

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Dead Channel: Fuses?
« Reply #1 on: April 23, 2007, 10:48:26 PM »
The first thing I would personally try is cleaning ALL of the slider controls and pots.(With the proper contact cleaner) If you aren't experienced with electronics, I suggest that you have a tech look at it if it turns out to be more serious. I never recommend attempting to open up and work on the electronics if you are a novice.

Steve O
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 270 Butterfly Grand
2004 Hammond XK3
2009 73A Rhodes Mark 7
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2020 Kawai CA99
....and a few guitars...

Offline paulb

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Dead Channel: Fuses?
« Reply #2 on: April 24, 2007, 10:01:04 AM »
I don't think it is dirty pots or sliders.  It's probably not the fuse either, but that is easy to check.  Take out the 10 screws that hold the amp in the cabinet and gently lean the amp out.  Right where the speakers plug in you will see the 2 fuses.  One for each channel, 4A I think.  Simply change them around and see if the channels switch as to which is working.  If the A channel works and the B doesn't, then you know it's the fuse.  If the problem is the same, then the fuses are fine and your problem is more likely a power supply.   It may just be the connections where the main wires plug in to power the circuit boards.  P1, P2 and P3 on the circuit board diagrams in figures 11-5 and 11-6 of the service manual.  If this is the issue, then the joints may need to be re-heated and soldered up and make sure the connections are clean at the plug ins.  Also make sure these are all plugged in securely.  Just stay away from the capacitors when touching things.  But as always, check the fuse first!  Paul
1977 Mark I Suitcase 73
1976 Mark I Stage 73
1975 Yamaha U1

Offline Benjamin

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Dead Channel: Fuses?
« Reply #3 on: April 24, 2007, 10:52:06 AM »
Thanks for all the advice folks, I'm having a tech friend of mine (not a Rhodes expert) come over and help me not kill myself. I'll let you know how it turns out. Thanks again!

Ben

Offline Mark II

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Dead Channel: Fuses?
« Reply #4 on: April 24, 2007, 01:01:49 PM »
i wouldnt mess with the knobs/sliders aswell, dealing with regular contact cleaner on pots and espescially sliders is pretty dangerous. you can destroy more than you might be able to repair.
first I would try swapping the fuses.
If that doesnt succeed you might want to swap the power cables of both main amp sections. with that strategie you are able to find out if its a power related thing or if the main amp has blown.
asking a tech to help you is a good idea.
you find all schematics you might need in the service section of this site. they are listed as "100W Suitcase and Janus I"

http://www.fenderrhodes.com/org/manual/ch11.html

good luck

Mark II
Rhodes Stage 73 Mark II 1980 / modified Peterson Suitcase Preamp

Offline Benjamin

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Dead Channel: Fuses?
« Reply #5 on: April 24, 2007, 02:16:37 PM »
A big thank you all around for the replies.

Got in there this afternoon, and sure enough one of the fuses was fried. I'll be heading to the hardware store tonight for a replacement. Simple fix, thank god!

Ben

Offline Benjamin

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Dead Channel: Fuses?
« Reply #6 on: May 04, 2007, 03:38:47 PM »
UPDATE: It looks like it may be tech-time for my old Rhodes. I changed the fuse and had my channel back, until this afternoon. Same channel is out again, and I'm guessing I blew another fuse. Anyone else experience a constant fuse-blowing situation with their suitcase? Also, while holding a mic cable connected to a computer interface, I got some electric shocking from touching the outside of the power amp (i.e. screws). Not sure if this is related somehow, but leaking electricity seems to bother me more than fuses. Sound common?

Offline blueberryjam

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Re: Dead Channel: Fuses?
« Reply #7 on: August 17, 2021, 11:51:57 PM »
UPDATE: It looks like it may be tech-time for my old Rhodes. I changed the fuse and had my channel back, until this afternoon. Same channel is out again, and I'm guessing I blew another fuse. Anyone else experience a constant fuse-blowing situation with their suitcase? Also, while holding a mic cable connected to a computer interface, I got some electric shocking from touching the outside of the power amp (i.e. screws). Not sure if this is related somehow, but leaking electricity seems to bother me more than fuses. Sound common?

it's a long shot seeing that this post is over 14 years old, but Benjamin, have you ever managed to fix this and how? Experiencing the exact same issue!