Question about dead pickups on my Mark II

Started by 400hands, February 05, 2025, 03:42:21 AM

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400hands

Hello! I recently bought a Rhodes Suitcase 73 Mark II for a great price dude to its condition. I know Mark II pickups are known to fail in huge amounts, but my specific model is stamped "4179", making it a 1979 Mark II. These are widely similar to 80s Mark IIs with a few differences, like wooden keys, but I also notice that it has red (not white, see my only other post for pictures) 1974-1979 era pickups. I'm hoping that this means I may not have 20, 30, 40 dead pickups.

I followed the Vintage Vibe guide on using an ohmmeter to read the groups of 3 pickups - some read at 180 (the DC resistance for a single pickup), and some read closer to 90. I am generally experienced in tech work and my general understanding is that a dead pickup would read nothing at all. When I do the screwdriver test it seems like just about everything above say the 10th key is dead. I don't see any visible breaks in the wire, although I did notice a strange grounding issue (again, see my other post for details, but right now I'm most concerned about getting it to start making noise again). Could there be a break somewhere causing this mass pickup silence? It's a beautiful instrument and it's been a dream of mine to own one - I keep laying my ear on the wood and playing just to hear the tines ring out - Still Crazy After All These Years...

LeoGrossman

Saw your reply to my thread, and figured I would offer my 2 cents. When you measure resistance across groups of three, here is how to interpret the results:

60 ohms - No bad pickups
90 ohms - One bad pickup
180 ohms - Two bad pickups
Overload - All bad

I had an issue similar to you, where it seemed as though all of the pickups above a certain key were broken. Turns out, there was one group of three that read overload, meaning the entire group was out, and this was a breakpoint in the entire circuit. I jumped this section with a jumper cable and voila, the upper half of the keyboard sounded just fine.

It drove me crazy trying to decipher if what I was hearing was the tines or the signal. I hooked a 1/4 inch cable into the top jack of the pre-amp's effects loop, ran it into my DAW, and tested with headphones. In my case, many of the pickups are indeed dead, and it is between repairing or rewinding them for me.

jupitervintagepianos

#2
The white sleeved pickups in Mark II are notorious for failing. I believe it was a drop in production standards that led to this increase in failure rate. So if you don't have them then thats great!

As Leo has said above, when measuring each terminal of a Rhodes pickup, the resistance is around 180 ohms. If this is a little above or below it is ok.

Pickups in the harp on a 73 note piano are wired in groups of 3 for the vast majority of notes, and 4 for the bottom four notes. The actual number of pickups connected together by a single piece of wire is usually 6 (7 at the very bottom), but because the connection to the adjacent set of pickups is only through one wire from one end of a pickup, this actually means that only 3 are connected directly. This means that the resistance value is affected by how many are connected.

In working pickups for groups of 3, placing your multimeter at each terminal of a pickup, the reading should be around 60 ohms. For the bottom pickup group of 4 together, the reading should be around 45 ohms.

Essentially it's a division of 180 ohms divided by how many pickups there are. So 180/3 = 60.

Now let's say one pickup is dead in a group, how do you find it? Well I would test that the pickup is actually dead by using the multimeter to measure the resistance. Here's the formula for that for groups of three pickups. Remember values are approximate:

3 pickups group:
60 ohms - all pickups work correctly
90 ohms - one pickup is dead
180 ohms - two pickups are dead
Error/OL - all three pickups are dead

This is because the pickup that is failing is usually shorted, meaning there is zero resistance so it is not read. For the group of 4 pickups at the bottom, the values will be divided by four so:

4 pickups group:
45 ohms - all pickups work correctly
60 ohms - one pickup is dead
90 ohms - two pickups are dead
180 ohms - three pickups are dead
Error/OL - all four pickups are dead

If you have all pickups in a section that don't work, this can cut out the circuit for the rest of the Rhodes. As the current is coming from the RCA socket on the left, it means that notes that are higher up may not work if a section of pickups is dead in the lower end. You can use crocodile clips and wire to bypass this section and test if the rest is working. I once had a piano with 40 failed pickups that didn't make a sound at all!

For 88 key pianos the wiring is usually in groups of two for the bottom third of the piano, and then groups of three for the rest until the very top. So the reading for groups of two should be 90 ohms for two working pickups, 180 for one dead, and zero for both dead. The top four pickups are wired in series so each will read 180 ohms if working. See the Rhodes wiring charts the Vintage Vibe have on their website.

And of course for 54 note Rhodes and early 73 pianos the wiring is in series, which means that if one pickup goes they all do! Very annoying.

Now to find the one(s) that doesn't work! Usually the best trick is to tap the end with a flathead screwdriver. If it makes a healthy 'thunk' sound then the pickup works correctly. Most of the time, the pickups in the set of three (or four) that don't work will not make this sound or it will be very quiet.

If this doesn't work you may need to disconnect the pickup wires in order to measure each one in the set individually. However this is a pain and resoldering the old wire can be tricky, so do this as a last resort.

Usually then this is a case of clipping the dead pickup, removing it, installing a new one and soldering everything back together.

Notes: there is also the issue of demagnetised pickups, which can show as normally functioning pickups but have a very thin or sometimes dead sound. This usually happens to many at once however and should be explained in another post!
James Beckwith

Jupiter Vintage Pianos
Electric piano servicing and repair in London and UK

james@jupitervintagepianos.com

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