Messages

I had the same issue. You can read a report here :
https://ep-forum.com/smf/index.php?topic=10556.0
For all purposes.

I also updated all the electrolytic capacitors on the preamp PCB (mine is a Janus). It works fine so far. As Spave stated, I also recommend seeking the services of a professional technician if you are not familiar with the electronics field.

An example of a cold solder joint here :
https://photos.app.goo.gl/6s4HVKZ1X8m1efJK8

Hello Noah,
No response to your message so I'll give it a try. I am not a professional ; just the happy owner of a 1977 Rhodes suitcase that I maintain. However, I have some knowledge of electronics.
I had a tremolo problem on my piano a few years ago. I was able to resolve it by refurbishing the electrolytic capacitors, especially those on the power supply board and amplifier boards. You can find the report of this operation on the following link.

https://ep-forum.com/smf/index.php?topic=10556.0

For your problem, my instinct leads me to suspect these components. If they have never been changed, they are probably out of order and may be the cause.
I hope this will help you. Please let us know.

Hello Jean-Pascal,
I went to YouTube and Soundcloud.

I really liked...
- tunes/composition
- the style... original
- the playing

I have good headphones (actually the ones you use in the studio). The sound is good, even with the average streaming quality. The drums seem further away though, perhaps by choice.

Could you tell us about the effect pedals you use? And other sound modules ?

Keep up the good work.

Bill

Good point.
I was tought electronics in the early 90s. I learned that some types of electrolytic capacitors were designed with a self-healing feature. This required voltage to be applied to them regularly, at a reasonably high level, for the self-healing process to occur, thus preventing early wear.
On the Electrolytic Capacitors Wiki page I see that most modern electrolytic capacitors "can be stored for up to 10 years without problems" (i.e. without any voltage applied). My point about the voltage rating is therefore debatable/obsolete. Indeed, it seems that having a stock of 100V capacitors to meet all needs is a reasonable choice today.

How'd you end up feeling after beefing up the main cap values so much? I've worked on a couple of these for friends and they seem to have less clean headroom than I expected

I wrote a detailed answer and posted it on the page : https://ep-forum.com/smf/index.php?topic=10556.0

Some comments on the choice of components:

I looked for the same value in capacitance (F) and operating voltage (V) on my supplier's website, often in vain. Then I chose the next higher value. The same components with the same values and sizes may be difficult to find due to a change in manufacturing standards. My choice was also oriented towards manufacturers renowned for their reliability, restricting the choice.

About capacity:
These electrolytic capacitors have the function of smoothing the rail voltage (+ ground -). Replacing these capacitors with others of higher capacity is not a problem. In fact, the higher the better (in the Hi-Fi field you can find crazy capacitance values). In product design, the value is chosen taking into account a reasonable capacity for the needs of the device (i.e. providing current to the speakers when hiting a key at full volume) as well as other considerations including headroom and cost. Here, a capacity 2 or 3 times greater is not that much greater.

About operating voltage:
An operating voltage 2 or 3 times higher than required does not do justice to the device. The capacitor will not perform at its best and would be susceptible to wear out (not to mention wasting headroom and money). However, never replace a capacitor with one that has a lower operating voltage value. There is a risk of failure here.

About size :
As you can see in the photos, some replacement capacitors are smaller than their original counterpart.
Some are bigger. I made sure they would fit on the PCB before purchase.
Some had to be the same diameter: C1 and C2 because they are mounted on a clamping ring.
The PSU + AMP unit is not in an enclosure so the height of the components is not an issue.

Hello NZM,
The good news is that yes, this has been fixed. The second good news is that I recorded what I did:

A few weeks after this technical intervention, my piano no longer worked at all. I assumed the electrolytic capacitors in the PSU and AMP were all bad, as they are prone to aging with heat and time. My second-hand piano had never been serviced since the 1970s.

You will find details of this intervention on the following subject:
https://ep-forum.com/smf/index.php?topic=10556.msg58811#msg58811

Then I had a feeling that this faulty power supply was the cause of my vibrato problem. So I went back to the original configuration, removing the jumper. I was right. Since then, it has worked well.

In summary, the tremolo will not work properly with a faulty power supply. Upgrading the PSU+AMP with new electrolytic capacitors will do the trick. My advice is to also upgrade the preamp soon after and you will have a reliable piano for years to come. Find more about this here :
https://ep-forum.com/smf/index.php?topic=10294.0

[but not only]

Hi Spave,
Good question.
I know nothing about amp fires, so I won't discuss that topic. If you unplug your Rhodes from the electrical outlet after use and if they have their proper fuse, I'd say you're safe.
However, we can talk about repair or maintenance.
Of the electronic components in your Rhodes, electrolytic capacitors have the shortest life span. This type of capacitor has a lifetime of 1000s of hours. This information is usually found in the manufacturer's data sheet. But this varies a lot with actual operating voltage and operating (ambient) temperature.
If you use your Rhodes 6 hours a week, these capacitors will be out of use in 10 to 20 years. If your Rhodes has never been serviced, the capacitors inside are worn out. The situation you describe can be caused by this, but not only...
If you maintain your Rhodes (i.e. change worn components), you will have a more satisfying experience with your instrument.

But what if you wait for a complete breakdown?
In some cases, a capacitor can leak and spread chemicals on the PCB, which is not good for other components. It can also "pop" with the same result, plus an acrid smell. It can cause a short circuit, dragging other components down.

My opinion is to change the capacitors if they are too old. They are located on the 2 amplifier PCBs, on the power supply PCB plus 2 on mounting clamps, and on the preamp. Changing caps is not a big deal if you know how to use a soldering iron and a desoldering pump. You can find maintenance kits on the website of online dealers. If you are not too confident with this, you'd better ask a professional technician because there is a safety hazard with the current here. He could find other issues too, not adressed only by the capacitors.

An example of successful maintenance here: https://ep-forum.com/smf/index.php?topic=10612.0

Keep us in touch.

Good news. Keep grooving !

Hello,
I suggest you check each speaker individually. You can use a 1.5 V battery for this. Disconnect the speaker from any equipment. Briefly connect the battery to the speaker terminals via an electric cable, pole to pole. The direction of polarity does not matter since the loudspeaker receives a +/- electric signal around 0V. If the loudspeaker works, you will see the membrane move forward (or backward) a few millimeters. You will also hear a pop.
If nothing happens, your speaker may be out of service.
You can also connect your multimeter to the terminals of each speaker, in ohmmeter mode. And see what happens.

Thanks for this feedback. Enjoy your Rhodes now !

You're welcome. If it feels right for you, then it is right. 

My piano is the same as yours.
Yes, the caps are canister style. Do not forget the two big blue caps. They are not on a PCB but on a mounting clamp.
I posted more pictures on the "PSU and AMP update" topic.
https://ep-forum.com/smf/index.php?topic=10556.0

Hello,
I'm not sure if this is what you need, but there are screws at the bottom of the wooden frame: "support block mounting screws"
https://www.fenderrhodes.com/org/manual/fig9-6.gif

It would be a good idea to mesure the +/- power amp rail voltage and the +/- preamp rail voltage, with load (5 pin connector connected) and without load (5 pin connector disconnected). As reference before servicing the appliance. (Keep your hands away from any live part when doing so). While the enclosure is open, I like to do a thorough visual inspection, looking for brown areas on the PCB or on components that may have overheated.

Hello,
I had the same issue. It is likely to be the power supply. If the electrolytic capacitors have never been changed, they are probably out of order. See the following topic with the repair :
https://ep-forum.com/smf/index.php?topic=10556.0

If you order electronic parts for the piano, it would be good to change the electrolytic capacitor of the preamp too :
https://ep-forum.com/smf/index.php?topic=10294.0

Please note to check parts reference for your piano version (mine is Mark I Janus preamp).

Keep us in touch.

Bill

Hello,

So a DI-box does something different than an audio interface?

The DI-box allows to pass from the "unbalanced" technology to the "balanced" technology, which is more effective to carry an audio signal on long wires. You can find many articles online about those technologies and their difference. A summary...

Unbalanced technology :  The audio signal is carried by two wires : the audio signal lead and the reference lead (also used for shielding). A cable with mono jack connectors / Tip and Sleeve (TS) is typically used in this technology. Eg : An electric guitar to its guitar amp. This technology is sensible to interference. The longer the cable, the more interference the signal can get. Typical length : less than 2 m.

Balanced technology : The audio signal is carried by three wires : audio signal (+) , audio signal (-) and reference lead (also used for shielding). A cable with XLR connectors is typically used in this technology. This technology is much less sensible to interference. Long cables can be used between appliances, on a live stage or in a recording studio. Typical length : 1 m to ... 30 m.

For example, my unbalanced cable from 'accessory 1' output to DI-box is 60 cm (2 feet) long and my balanced cable from DI box to mixing table is 8 m long. See picture :
https://photos.app.goo.gl/EtesG8RzDNvKZ3nb8

An other DI-box feature : it isolates the two appliances. This is usually achieved by the use of an audio transformer, so that there is no direct electrical connection between those two, avoiding ground loop, which is a source of hum.

What tube preamp do you use?

I don't have enough experience/knowledge to recommend one or an other... I found a useful post from "The Real MC" here :
https://ep-forum.com/smf/index.php?topic=10355.msg57720#msg57720
You may also find good advice on Amps and recording techniques on the forum : https://ep-forum.com/smf/index.php?board=3.0

And why are you using a symmetric XLR cable?

My preamp output is balanced (=symmetric) with XLR connector, as required.

And am I right that 'accessory 1' output is the direct harp? Or do I need the RCA output in the inside of the Rhodes Piano?

The harp pickups are connected to the RCA and the RCA to "accessory 1". So you can conviniently use "accessory 1".

Hello,
I am not a pro, just a "Rhodes lover" so I go for it.
I listened to your samples with a pair of good headphones and here is what I found.
In the first sample (harp > audio interface), I hear a hum.
Make sure you activate the "INST" setting on your input channel and use a short cable between harp output and channel input. Move any electrical appliance away from your setup. As a last resort, disconnect the laptop charger and record on battery. Yes, you can try to use a DI box there in between if you can get one. It will add galvanic isolation on the signal path.

However I hear no hum at all on the second sample. The sound is clearer too but maybe because the recording has a higher level. In my opinion, you have a good enough solution to record your Rhodes here. Plus it allows you to use the Rhodes tremolo and effect loop.

Yes, why not use some other preamps ? It is a game changer. Personnaly, I often connect...
harp >>> tube preamp with EQ >>> mixing table (via a symetric XLR cable) >>> sound system or headphones.
I also add guitar pedals (compression, reverb) before the preamp with TS cables. It gives me a bigger sound. And when everything is bypassed, I have my original Rhodes sound... great too. This option is mono and forbid the use of the Rhodes tremolo.

Some other ways to record a Rhodes :
- Put a microphone in front of one cabinet loudspeaker to catch the suitcase sound.
- Put two microphones in front of two cabinet loudspeakers (one each) for tremolo (and stereo).
- Connect the harp output to a guitar amp (as for a stage piano) and put a microphone in front of the loudspeaker.
Those options can be tidious and expensive as the right microphones, room acoustic treatment and technical skills are required for a satisfying result. You can give them a try if you can, it is always an interesting experience.

Most important, the inner piano adjustment. Again I am not an expert but I really like yours. I wish mine were as fine. You have a nice raw material to start with, for recording, mixing and playing with effects.

Keep us in touch.

Will

Hello,
A few months ago my piano amp was not working at all. I assumed the power supply was faulty. I ordered parts to restore the power supply and amp modules and made the change. It is working fine now. Here is a report of what I did, for the record.

My piano is a 73 suitcase Rhodes Mark I piano ref. 3077. No upgrades have been done on this power supply or on the amplifier modules so far. It was time to change all the electrolytic capacitors. I also changed the twisted wires to suitable 0.5ohm resistors. I did not change the transistors.

You will find a picture of the finished product here. Zoom in for details : https://photos.app.goo.gl/5TqvNPgFRDPxxpE1A

The part list. At the end of each line, what I ended up choosing.

Amp   capacitor   Electrolytic   C1   4,7uF / 25V NP       AXIAL    >>> Mundorf BG50 4.7uF 75V      
Amp   capacitor   Electrolytic   C2   1uF / 16V NP          AXIAL   >>> Mundorf BG50 1uF 75V   
Amp   resistor   Wirewound   R18-R19 R20-R21   0,47 ohm  -  5W      >>> Royal 0,47 ohm 5W
         
PSU   capacitor   Electrolytic   C1 C2   1000uF – 35V - 60 mm AXIAL   >>> Jamicon 2200uF 35V
PSU   capacitor   Electrolytic   C3 C4   500uF  -  15V - 40 mm AXIAL   >>> Vishay BC-021 470uF 25V
PSU   capacitor   Electrolytic   C1 C2   11000uF – 40V – diam 50 mm    >>> F+T GMB 33000uF 40V

It costed me 52 euros inc. VAT + 8 euros delivery = 60 euros in total ie. US$ 69 in jan 2022.

The Vishay 1000 uF were not available at the time of purchase so I ended up putting Jamicon spare cap I had from a PSU kit. Not the best choice. I will change them next time.
I left a gap between the resistors and the PCB when I soldered them. Those components are likely the get hot so they need space to dissipate heat.
I soldered an insulated terminal to the wires connected to the 33 000 uF capacitors. They have bolts.
I cleaned the PCB with 95% alcohol, a toothbrush and a tissue to remove flux.
The amp +/- rail shows 28.6V and the preamp rail shows +/- 14.6 V. Good !

Feel free to ask if you need more details.

Will

Hello !
Vintage Vibe has a reseller in Europe, ep-service.nl
Cheers !

Interesting topic. My second-hand suitcase Rhodes has new speakers, all 4. I've always wondered if those were the best match for the cabinet. They sound good to me but I never heard the original version to form an opinion.
Tell me if I'm wrong ...
The design of a cabinet depends on the characteristics of the speakers. Nowadays, special software is dedicated to their design. Replacing the original speakers with new speakers requires that their characteristics be close to the original, or suitable to the cabinet.
Is there a place where we can have the characteristics of the original speakers? To compare with speakers on the market? And especially to those mentionned by Frenchji (which I also found on the web as successors to the first)?
Or isn't it that important ?
There was a webpage about the speakers on the Rhodes website, but it has been removed...

Hello Sean,
Well spotted. Yes I should have mentionned that the right side of the PCD has not the original layout. You got the right link that explains why.
I did basic tests of the LDRs : 0.6V at led pins and resistance at opposite side, without unsoldering them. I saw nothing wrong here. They seem to work fine however, as the vibrato is working fine now, with front panel led disconnected.
I keep in mind your OpAmp advice for the next time I will put my hands into it. But not soon ; my next task is power supply and amp upgrade.
I will update this thread if I have further advance.

Hello Frenchji,
I am not the most experienced user here but here are my tips.

Only one side of the speakers works [...] What is the best way to test the speakers to make sure they are fully operational? 

I usually use a 9V battery and connect it briefly to the poles of the loudspeaker. You can also connect it to the tip and sleeve of the jack connected to the speakers. You should hear a "pop" and see the membrane moving forward (or backward if reverse connection). This is very basic testing of course.

...the amps needs some work.  There is a very obvious blown resistor ...

Your amp needs some electronics diagnostics to understand why the resistor has burnt. Replacing failed components would keep the circuit close to original and shouldn't be too costly.

No Tremolo!  When Tremolo is engaged...

Same here. Some diagnostics are needed to find out what the problem is.
Here are two topics to start. Be aware that my Rhodes has Janus preamp (without bulb)
https://ep-forum.com/smf/index.php?topic=10265.msg57985#msg57985
https://ep-forum.com/smf/index.php?topic=10290.msg58076#msg58076

Last, your amp, preamp and power supply need to be recaped indeed. Electrolytic caps do not age well. You can find rebuild kits on specialized suppliers online shops which are well documented and inspiring. Here is a topic about my preamp upgrade :
https://ep-forum.com/smf/index.php?topic=10294.0

I did the upgrade last january, as described in the previous post. I kept the original polypropylic caps. I changed the ceramic caps to WIMA MKP types (except C2 120p which I forgot to order). I decided to change the resistors on the signal path but I am not sure it is that relevant (I tend to overdo it sometimes). I also thought of changing the cables but decided not to do it (yet). I cleaned the board carefully with acetone and put everything back in place.
How does it sound now ? Yes, it sounds good, clean and loud. I am satisfied.
Some pictures :

Hello Sean,
It's a good idea I wish I had tried. I was focused on the led indicator as the oscillator works fine without it.
I may try this the next time the circuit will be on the lab bench but it won't be until... months. I keep my spare time to train my piano skills now... and enjoying my Rhodes. I will update this thread it this case. Many thanks Sean for your helpful replies.
Will

[One interesting thing to notice :]

I got back to my vibrato issue as I had few days off. I have spent quite some time to know more about the cause and eventually find the cure. To this day, the issue is not solved but bypassed. It is OK for me "as is". This is what I have done, just for the record.

I took the preamp out from the piano and I built a separate +/- 15 V lab power supply to see if I could reproduce the problem without the Rhodes power supply. Which I did. The Rhodes power supply is cleared.

I changed all the electrolytic caps which were all faulty. I also changed a non-polarised cap on the oscillator (C8). I removed the vibrato switch and put a shunt in place. I cleaned the board carefully. With no better result.

One interesting thing to notice : the voltage between the -15V rail and ground drops to few volts when the output of the oscillator (op-amp pin 7) is at low state. This is why the pilote indicator led (LED 4) gets dim. And this is why the sound gets distorted. The signal is clipping. This can be observed only when the oscillator is at a low rate as the the voltage has enough time to drop.

I have the feeling that the op-amp output at pin 7 is short-circuited to ground when at low state, draining the power supply. My guess was that the vibrato indication led or its transistor was the culprit. Disconnecting them from the oscillator did the trick indeed. However I did my best to find a failure there, without success. I even replaced the transistor to a new one... it did not do the trick.

I ended up leaving the vibrato indication disconnected from the oscillator output and left the led on : I removed R26 and the transistor. I added  a jumper from R28 to the led.

Back to the piano, the preamp and oscillator work fine now. Without vibrato indication however.

I also connected the third pole of the switch to ground.

Picture here : https://photos.app.goo.gl/Srw82URnJhFiVtXr9

[One interesting thing to notice]

I got back to my vibrato issue as I have few days off. I have spent quite some time to know more about the cause and eventually find the cure. To no avail but here is what I have done, just for the record.

I took the preamp out from the piano and I built a separate +/- 15 V lab power supply to see if I could reproduce the problem without the Rhodes power supply. Which I did. The Rhodes power supply is cleared.

I changed all the electrolytic caps which were all faulty. I also changed a non-polarised cap on the oscillator (C8). I removed the vibrato switch and put a shunt in place. With no better result.

One interesting thing to notice : the voltage between the -15V rail and ground drops to few volts when the output of the oscillator (op-amp pin 7) is at low state. This is why the pilote indicator led (LED 4) gets dim. And this is why the sound gets distorted. The signal is clipping. This can be observed only when the oscillator is at a low rate as the the voltage has enough time to drop.

I have the feeling that the op-amp output at pin 7 is short-circuited to ground when at low state, draining the power supply. My guess was that the vibrato indication led or its transistor was the culprit. Disconnecting them from the oscillator did the trick indeed. However I did my best to find a failure there, without success. I even replaced the transistor to a new one with no better result.

I ended up leaving the vibrato indication disconnected from the oscillator output and left the led on : R26 and transistor removed and jumper from R28 to led added. 

Back to the piano, the preamp and oscillator work fine now. Without vibrato indication however.

This initial design was changed to a later one, as Sean stated in Reply #1. More rational indeed. I also connected the third pole of the switch to ground as suggested by 1way2life, who borrows this concept from this later design.

Picture here : https://photos.app.goo.gl/Srw82URnJhFiVtXr9

The issue is bypassed, but not solved and remains a mystery to me.

Hi 1way2life,

"shunt the base of Q1 to ground when the vibrato is off"

I drew two schematics to think about it. Which one is suitable to you ?
https://photos.app.goo.gl/n9P43wkdBMC9QpAg6
https://photos.app.goo.gl/c67NybXEV5G5EBRn6
The second one uses a DPDT switch.

Hi 1way2life,
Thanks for your reply.

Which wiring did you set up ? Out of phase (p.5)   or   in phase (p.3) as referred to in the vv document ?

I checked the rail without preamp (+14.58V  -14.58V) and with (+16V   -11V). Q1 tested (P>N 0.6V) and nothing wrong. A topic is opened at https://ep-forum.com/smf/index.php?topic=10290.0

"shunt the base of Q1 to ground when the vibrato is off" Which preamp version do you have, as referred to by sean ?

Hi,
I have the same vibrato issue. I checked my speakers and they have been changed too to some 8 ohm speakers by previous owner, obviously. The original parallel wiring was kept too giving 3.5 ohm for the PA output. I changed to series config, to no avail to my issue. Still investigating.

By the way, I found this vv document which is getting me confused. In page 4, I don't understand why Janus 8 ohm speakers should be kept in parallel. The page 5 series and phase invert config seems best to me. Which I chose.

Hello

I have the early version of Janus preamp ref. PART NO.013487 which I intend to upgrade. You can find the schematic diagram here.
These are my thoughts and questions about its upgrade which I submit to your comments.
You can find the part list here to follow the subject.

The LM1458 OpAmp on signal path can be upgraded. I have a pair of Burr Brown OPA2134PA which I intend to use. They have the same pinout config. And add their package.

The electrolytic capacitors need replacement after more than 40 years of services.  I will choose Panasonic (FC series), Nichicon (KA, FG, KW), ELNA (not Silmic II)... The relevant capacitors are C8 C20 C12 C13 C14 C15 C3  and non-polarised C4 C6 C16.

Black and round shaped capacitors seem to be polypropylic. If that is the case, they are good quality caps and age well so they must be kept in place, right ? Those are C11 C1 C9 C5 C7 C10.

Small and flat caps are ceramic. From what I know, they are not suitable on audio signal path. On the schematic, they seem to help stabilise the OpAmp (C2) and to suppress unwanted high frequencies (C17 C18 C19). Am I right ? Are they worth to be changed ? For what type ?

I don't know the quality of the present resistors and I am wondering if a change to modern low noise metal oxyde resistors would be beneficial. I have an assortment of them.

The transistor and diodes are not in the signal path and don't need to be changed, unless faulty. Same for the vibrato speed pot.

Linear bass and treble pots and vibrato intensity pot are on the signal path. I don't plan to change them as they make no crack.

Hello,

With the preamp disconnected, what do the power feeds coming from the amp cab measure?

I get +14.58V and -14.58V. The drop in tension is coming from the preamp indeed. I also removed the A2 oscillator IC from its socket and I still have this -11V instead of -15V. So the OpAmp is not faulty.

check (...) continuity of the ground terminals

I checked all the bits with the multimeter and it is showing continuity.

Check that the 100%u03A9 current-limiting resistors are still in good shape (...) and close to 100%u03A9.

Yes to both, they are all fine.

take a good look at the PC board where the switch mounts.

I did and found nothing. However, I am suspicious about the switch, instinctively.

My to-do list :
- Draw up a components list to upgrade the preamp board (I will make a post very soon about this) and order the components
- Remove the components form the board. Remove the solder with a pump. Clean the board with care.
- Populate the board with new components and wires. Clean the flux from board. Look for any bridge between traces.
- Let you know...

Hi Sean,
I carefully read your post. I did few things this evening but I will do more this week-end. Some answers however :

A thick piece of plastic is already in place, stuck on the enclosure below the PCB. I don't know if it is from factory or if my friend put it in place but it is done very carefully.

The strips had some oxyde dust on them. They had some flux in some place too. So I cleaned them this evening. They need some more cleaning so I will start again this week-end. A leakage may occur here.

Switch case test still to be done.

The oscillator is actually running. I don't have a scope but at low frequency, my multimeter shows the voltage output swinging from + to - at OpAmp output pin 7. At top speed, the frequency-meter shows 15 Hz.

Removing the "vibrato indicator" LED causes the symptoms to occur, even if the switch is off.

I made further tests with interesting results :
When the vibrato is off :
...The positive power supply rail measurement is +16V (+15V expected from datasheet). The negative rail measurement is -11V (-15V expected from datasheet).

When the vibrato is on (at low frequency) :
...and when the oscillator output at OpAmp pin 7 is hight, the rails remain the same as above (+16V and -11V). The "vibrato indicator" led and the "pilote indicator" led are fully lit. The sound is normal.
...and when the oscillator output at OpAmp pin 7 is low, the power rails change to +26V and -0V. The sound becomes weak.  The "vibrato indicator" led is off which is normal. The "pilote indicator" led weakens too which is unusual. The reason is there is no more potential difference on its poles, between negative rail and ground.

There may be a ground reference issue because the + and - rail difference remain the same. Maybe an OpAmp failure...?

To be continued.

Hi Sean,
Thanks for your answer. The switch is connected to pin 7 of OpAmp IC A2 on one pole and to R26 resistor on the other pole so I deduce the Fig11-1 applies.
The board reference is
PART NO.013487
ASSY NO.013488
ECI-2
VO
so yes, 013...

Hello,
This is my first post.
I am the lucky owner of a 73 suitcase Rhodes Mark I piano ref. 3077 for two years now. I am a regular reader of this forum ever since and I would like to thank the members of this community for their contribution. I would like to pay tribute to my friend Pierre who offered me to be the second owner of his piano, and who passed away a few months ago. I have been confident enough to restore maintain and adjust my piano so far. But I now have an issue that I cannot fix by myself, which you may have gone through.
On the Janus preamp, I have a drop in power when I switch the vibrato on. The sound fades out and the LEDs light weakens. The switch seems to engage a short circuit. The power comes back to normal when the switch is turned back off. I don't make this test often as I would not like to cause a power supply failure.

I removed the preamp, opened the enclosure and I see nothing wrong. No smelly or burnt component. I tested the transistor and the diodes with a multimeter and they are fine. I sought a short circuit between +15V -15v GND and switch when the switch is on with no results.
One interesting fact is this phenomenon occurs also when I unplug the vibrato indicator led.

I could not find a topic about this. If you know of one please show me the link. Otherwise any advice or solution welcome.