Author Topic: Restoring Mark II no sound from harp  (Read 3033 times)

Offline dagodrummer

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Restoring Mark II no sound from harp
« on: May 07, 2012, 04:30:56 AM »
 This piano has been sitting for a long  time. The red wire from the RCA plug was disconnected
From the lowest pickup. I then replaced it with a piece of insulated copper speaker wire. I also
Hooked up a patch cord from the RCA to an amp. Also, I  sanded the L bracket and all ground
Connections. Still no sound. Maybe the tiny copper wire from the pickup coil is not connected
or perhaps I fried the pickup while soldering? When I touch the magnet on the pickup I hear
Some static out of the amp and when i touch the rear of the pickup the static noise is much
Louder. Perhaps I should check that pickup with a meter, but I 'd hate to cut any more wires
If it is not necessary.  I really like this piano and it seems to be a low mileage cream puff.
Any advice would-be greatly appreciated.

Offline David Aubke

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Re: Restoring Mark II no sound from harp
« Reply #1 on: May 07, 2012, 08:06:00 AM »
No sound from any pickup suggests a break in the signal path somewhere. Luckily, it's a pretty simple path. Assuming your piano is wired in the standard series/parallel configuration, it shouldn't be too difficult to isolate the problem.

There should be uninsulated wire connecting the pickups together. Sets of (usually) three are connected across both pickup lugs (parallel) and each set is connected to the next set by only one wire (series). The parallel wiring provides a redundant path for the signal so, within each set of three, if one pickup goes bad, your signal will still find its way. The one pickup will be dead but the rest of the piano will still work. For the signal path to be entirely broken, either all three pickups in a set must be bad, or the single connection between two sets must have failed - either broken or a bad solder joint.

You can do some testing by using a length of wire as a jumper to bypass sets of pickups. Touch one end of the wire to the hot terminal of the RCA and start touching pickup lugs, working your way up the scale until you get some sound from the piano. You can apply this jumper to any two pickup lugs to narrow your search range until you've identified the break in your path. Alligator clips make this job easier.

If your Mark II has pickups wrapped in white tape, I wouldn't be surprised to find an entire set of parallel-wired pickups has gone bad. The white-tape pickups frequently die prematurely.
Dave Aubke
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Offline The Real MC

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Re: Restoring Mark II no sound from harp
« Reply #2 on: May 07, 2012, 10:56:24 AM »
I have had the RCA jack go flaky on me.  I replaced it with a 1/4" jack, it fits the L-bracket with zero modification.

Offline dagodrummer

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Re: Restoring Mark II no sound from harp
« Reply #3 on: May 07, 2012, 11:05:45 AM »
Thanks very much for the helpful & intelligent information. It does have  the white tape
On the pickup coils and the 1/4" fitting is a great idea.  Thanks to all!

Offline dagodrummer

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Re: Restoring Mark II no sound from harp
« Reply #4 on: July 01, 2012, 02:19:14 PM »
Hello
I finally got some notes to sound by patching into some pickups from the positive side of the
Rca jack,but I am still not clear on how to isolate the bad pickups  with a patch cord. My
Mechanical background is not much help here.
I am  looking for that group of pickups that must be out. I have been able to get  sound from
Around middle c when I patch from hRca + to a pickup in that area. Getting some notes to
Sound only when patched into upper octaves.
Sorry to be so dense,but  I know I am almost understanding this.
I need a little more info about finding the break in the signal path.
Thank-you in advance
 :)

Offline sean

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Re: Restoring Mark II no sound from harp
« Reply #5 on: July 03, 2012, 11:38:29 AM »
Batterista Amico,

If you have pickup rail issues, all you have to do is search the forum for "crocodile" - makes perfect sense, right?

Here is my method of isolating the individual dead pickups:
http://ep-forum.com/smf/index.php?topic=3839.msg17262#msg17262

Get a few jumper wires with alligator clips on each end.  Auto parts store have them, Radio$hack has them, and big hardware stores should have them too (in the section where they have overpriced cable TV home-wiring kits.)

Basically, you use the alligator clips to short out sections of the pickup rail, this provides a bypass path for the signal to travel around the dead pickups, and you will get sound from the notes that are outside the regions that you short out with the alligator clips. 

Start with a large number of pickups to bypass, and then once you get some sound from any note that is not in the bypassed groups, move the alligator clips closer together (for instance, move the rightmost alligator clip six pickups to your left), and see if you still get sound.   If you still get sound, you can move the alligator clips closer together again, until you isolate the unlucky group of three pickups that are all dead. 

If you suddenly don't get any sound after moving one end of the bypass jumper wire, that means that you have exposed the group of dead pickups, and they are right between the old and new positions of that alligator clip.

Remember, you might have more than a single group of dead pickups.   You don't need alligator clips if you have a cooperative friend that can tap on the keyboard while you hold the ends of a jumper wire against the pickup terminals, but alligator clips make this a lot easier, especially if you have more than one group of dead pickups.

Once you have found all the groups of three-dead-in-a-row pickups, you need to hunt for dead single notes.   Leave the jumper wires with alligator clips connected to the pickup rail, so that all the groups of three-dead-in-a-row are bypassed.

Once you get sound coming from the harp that you can hear on your amplifier, then it is easy to hunt for individual dead pickups by either tapping on the pickup magnet tip with your smallest screwdriver (turn the volume down, because the CLACK sound is very loud); or you can simply play the keyboard, and listen for ghostly-quiet individual notes.  Remember, a note with a dead pickup can still make a very quiet sound through your amplifier, because the next-door-neighbor pickups will sense the vibration of the far-away tine.

Once you mark all the dead pickups, and buy replacements, or repair your dead ones, here is the basic method of replacing pickups:
http://www.fenderrhodes.com/service/pickups.php

If you are very energetic, you can re-wind your own pickups:
http://www.fenderrhodes.com/service/rewinding-pickups.php
(also search the forum for pickup re-winding advice.)


Buona Fortuna, Ciao,

Sean

PS - Since Apple closed mobileme, my links to the pdf diagram of pickup wiring is not online anymore.  But if you want it, send me a PM with your email address, I will send it to you as an email attachment.
The diagram is basically similar to the picture below, but it shows all 73 pickups.



(Ignore the "okay to split here" arrows and comments... they are remnants from another post on splitting the pickup rail.)

« Last Edit: July 03, 2012, 11:43:09 AM by sean »