# Rhodes MK-80 Keybed Zener Diode Replacement - Diode 4.7B or 7.5Z?

**URL:** <https://forums.syntaur.com/t/rhodes-mk-80-keybed-zener-diode-replacement-diode-4-7b-or-7-5z/9370>\
**Category:** Synth Repair\
**Tags:** rhodes, mk-80, dead-key\
**Created:** [March 10, 2026, 3:16am UTC](https://forums.syntaur.com/t/rhodes-mk-80-keybed-zener-diode-replacement-diode-4-7b-or-7-5z/9370 "2026-03-10T03:16:43Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![JEC](https://forums.syntaur.com/letter_avatar_proxy/v4/letter/j/d9b06d/32.png) [@JEC](https://forums.syntaur.com/u/JEC)\
**Post date:** [March 10, 2026, 3:16am UTC](https://forums.syntaur.com/t/rhodes-mk-80-keybed-zener-diode-replacement-diode-4-7b-or-7-5z/9370/1 "2026-03-10T03:16:43Z")

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[Rhodes] [MK-80] – [Which Zener Diode for Keybed?]

Hi, I need to replace some Zener Diodes on a Rhodes MK-80 Keybed. The service manual lists two Zener Diode part numbers but does not specify if the Keybed Diodes are…

**ZD MTZ4.7B** (part number **15019412** )

```auto
         or

```

**ZD 05 AZ-7.5Z** (part number **15019414** )

The PSU appears to deliver 5 volts to the Keybed so I suspect it’s the latter, **ZD 05 AZ-7.5Z** to give some headroom but I need to be sure.

Any help is much appreciated.

Cheers all.

JEC.

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**Author:** ![Travis](https://forums.syntaur.com/user_avatar/forums.syntaur.com/travis/32/1382_2.png) [@Travis](https://forums.syntaur.com/u/Travis)\
**Post date:** [April 4, 2026, 9:19pm UTC](https://forums.syntaur.com/t/rhodes-mk-80-keybed-zener-diode-replacement-diode-4-7b-or-7-5z/9370/2 "2026-04-04T21:19:08Z")

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Hey, this probably isn’t a zener diode but a fast switching diode if it’s one of the diodes in the keybed. In the service manual I think that’s the 1SS176 listed but a regular 1N4148 will work just fine.

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**Author:** ![Remodulator](https://forums.syntaur.com/user_avatar/forums.syntaur.com/remodulator/32/2046_2.png) [@Remodulator](https://forums.syntaur.com/u/Remodulator)\
**Post date:** [April 27, 2026, 10:46am UTC](https://forums.syntaur.com/t/rhodes-mk-80-keybed-zener-diode-replacement-diode-4-7b-or-7-5z/9370/3 "2026-04-27T10:46:33Z")

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I just finished repairing the keyboard PCBs on my MK-80 which had a lot of keys not working probably due to a liquid spill sometime before it came to me. Close examination of the topside traces showed certain areas blackened. Metering between pins or carbon pads either side of the blackened areas showed many tracks were open circuit. It’s hard to find replacement PCBs - Syntaur have them on back order, so I repaired the breaks by soldering in short sections of fine enamel wire laid flat against the board. I used clear epoxy to embed the wires so they stay put. Time consuming but effective. It now plays like new and I love the feel of this weighted keyboard.

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**Author:** ![sargfowler](https://forums.syntaur.com/user_avatar/forums.syntaur.com/sargfowler/32/2120_2.png) [@sargfowler](https://forums.syntaur.com/u/sargfowler)\
**Post date:** [April 27, 2026, 6:15pm UTC](https://forums.syntaur.com/t/rhodes-mk-80-keybed-zener-diode-replacement-diode-4-7b-or-7-5z/9370/4 "2026-04-27T18:15:40Z")

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Yeah, it’s a very common problem. The tracks start to corrode and break down.

Laying down wires to make the tracks is a very common repair.

You can use a UV cured paint and this is high temp and very fast curing.

Well done for fixing the keyboard and keeping it out of the dumpster!