Recap guide
Recap the Yamaha DX7 synthesizer
A well-known power-supply recap on a 1983 synth with a plain linear supply. A forum moderator posted values, and a mainboard tantalum keep-alive cap gets called out too.
Open the interactive checklist Tick off each capacitor as you replace it. It saves in your browser.
Worth a recap. Reports say it is a common and useful fix on this machine.
Which board do I have?
Boards changed during production. These notes come from the linked sources, and many are only partly documented, so check the board in front of you.
- DX7 Mk I (Medium confidence). How to tell: Original DX7 (Mk I); the Yamaha forum thread describes it as having a non-switching power supply. Capacitors: For USA 110 to 117V units the forum moderator gives original PSU values C17 and C18 1000uF 35V, C21 and C22 22uF 35V, C27 4700uF 16V, and suggests 50V, 50V and 25V or 35V parts. Main board caps are not itemised. Capacitor list differs from other revisions: not known. Source
- DX7S and DX7II (IID, IIFD) (Low confidence). How to tell: DX7IID has no floppy, DX7IIFD adds a 720K 3.5 inch floppy, DX7S sits between Mk I and II without split and dual modes. Capacitors: The thread gives no power supply or capacitor information for these models. Capacitor list differs from other revisions: not known. Source
Where to start
Clues from write-ups and forum threads, not a diagnosis. Low confidence means one thread or one repair; high means several write-ups agree.
- Power supply caps (Medium confidence). A moderator thread gives PSU references and ratings (C17/18, C21/22, C27) with advice to use 105C parts. It covers the Mark I only. Source
- Mainboard caps (Low confidence). One thread names a mainboard tantalum and some 1uF/50V and 2.2uF/50V caps, and notes the big PSU caps matter most. It also raises a caveat about the mains-switch suppressor cap. Source
- Battery and display symptoms (Low confidence). One worked example recapped both the PSU board and mainboard to chase battery and display symptoms, with a moderator guiding the measurements. Source
Tips, tales and maybes
Found in write-ups and forum threads. These are other people's reports, not tested by us. Check part references and values against your own board.
- Tip: C1 at the power switch (Medium confidence). A poster explains C1 is a special spark-suppression cap at the power switch: if it shorts it blows the fuse, and if it goes open you get a click at power-on. Treat it differently from the ordinary electrolytics. Source
- Tip: Match tolerance and voltage (Medium confidence). Posters advise keeping the same capacitance, using an equal or higher voltage rating, and not swapping a tight-tolerance part (they gave 1 percent) for a looser one. Check size and axial versus radial before ordering. Source
- Tip: Recap is not mandatory on a healthy unit (Medium confidence). The thread argues a working DX7 with no symptoms does not have to be recapped just for age. Look for hum, distortion or bulging first and check the voltages against the schematic. Source
- Watch out: Smoking AC-input safety cap (Medium confidence). A Mk1 thread says the safety cap at the AC input (C10 or C1) commonly fails in old units, with smoke or a burning smell, and gives the original as 0.022uF at 250V. The poster insists on an X2 or Y2 safety-rated part, not an ordinary capacitor, and says not to leave a Mk1 unattended while powered. Source
- Tip: Power switch that will not turn off, and change battery (Low confidence). The same thread notes some units get a power switch that fails to switch off before the safety cap goes, possibly tied to PSU board decay, and that a change battery message just means the memory backup battery is dead. Source
Before you start
- Boards changed during production. Check your board number against the guides before you order parts.
- A mains power supply can hold a dangerous charge. If you are not trained to work on one, have a professional do it.
Guides we used
This page and the interactive bench are built from these. They have the photos and the full detail, so please read them and support their authors.
- DX7 PSU Recap parts (Forum) by Miks (moderator) and Yamaha Musicians forum. Has a capacitor list. Only place with actual PSU cap references and ratings (C17/18, C21/22, C27) plus 105C advice; Mark I only
- Recapping a DX-7 (also TX-802, TX-16W and TX-81Z) (Forum) by Logix01001 and Yamaha Musicians forum. Principles, schematic with electrolytics marked, brand advice, and the mains-switch suppressor cap caveat; no parts list
- Yamaha DX7 MK1 problems (Forum) by Yamaha Musicians forum. Worked example: PSU board and mainboard recap with battery and display symptoms, moderator guiding measurements
The capacitor list
We have not checked a capacitor list for this machine yet, so none is shown. Follow the guide above for your board, then add the capacitors in the interactive checklist and it builds a shopping list for you.
Skip the sourcing
While you are in there
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Steps, tools and safety
The steps, the tools in top, middle and budget picks, and the safety list are the same for every machine, so they live on one page: How to recap, step by step.
Values are shown as published in the guides above, and boards changed during production. Check the board in front of you. A recap involves hot tools and, on some machines, dangerous voltages. You do it at your own risk.