Yamaha DX7 no ROM or RAM Cartridge read

Hello to all Syntaur Team and synth lovers.
Happy new Year !

I have a Yamaha DX7 MKI that I have received for servicing (usual dead battery and power supply recap, some switchs and pot replacement). The synth sound great after loading the presets to the internal memory via sysex. But there is a little big detail…when I try to call the rom or ram sounds, the DX7 recognizes the cartridges, but there is no sound and all the patches names from the cartridge are in the display with question marks or strange characters.

If I try to load them to the internal memory, I get no sound because the system copy this ‘error’ to the internal memory.

I have test the ram and rom cartridges in mine dx7 and both works fine.

I have check all the IC voltages, and even exchanged the PNB board, which is the first ‘entrance door’ of the flat cable that comes from the slot, with mine DX7, but still no correct rom/ram patches reading.

This DX7 is stock (no expansion boards) and I even have exchanged the ROM and RAM chips (IC14 and IC21) with mine DX7, but still no correct rom/ram patches reading.

I also execute the factory test, with no issues detected.

In the last years I had serviced many DX7, and other vintage synths, but first time I had this stupid issue. Checked and rechecked the schematics but and honestly now I’m stuck and don’t know what is happening

Any ideas or tips to debug this issue ?

Best regards,

the cartrides are good and you’ve eliminated alot more .It has to be somethin with the way the synth “reads” the cartridges.Apply the KISS principle and you’ll find it.Also I would stop taking parts from a working DX ,you could end out with 2 bad boards. Broken synths can be had cheap enough on Ebay,just send a seller that doesn;t appear to be in the “music” business,say someone that buys abandoned storage lockers a low ball offer and you might be surprised,hit the DX7 forums,if you’ve had this problem someone else has too…Its amazing how after all these years the DX7 still can rival todays boards…maybe one day I’ll find one i can afford or repair.I’m in atlanta,Ga USA and they sell fairly quickly locally around $750. Hard to keep one you’ve repaired when they fetch prices like that.

Did you do a factory reset after reassembling the unit?

Hi. Thanks for reply. Yes I did. But the factory reset on DX7 is nothing more nothing less than a copy (load) from cartidge to the internal memory. But when I load, nothing goes to the internal memory, and of course clean the internal patches.
Thanks any way

All I can think of is a failed tantalum capacitor on the motherboard. Tantalum’s fail in a dead short without leaving any visible traces, so each one will have to be checked. That would prevent propeller logic voltages from being read corrupting the data.

There is one in the battery memory circuit. If you internal coin cell battery reads between 3.6 to 5 volts its failed.

If you have a logic probe, test the buss lines if all are switching rapidly, of if one line is hung form a bad logic chip, its possible, but less likely.