Vintage Synth Repair

Hi Helge,

I had the same problem with a DX7-IIFD. There was no 500 khz and the 8 mhz clock input was clean. Address lines were floating and noisy. When I replaced the HD63B03YP MPU the synth would boot and load patches but there was no sound output from the YM3609 and YM2604 sound chips. The mix line was silent if I remember correctly. The MPU and YM chips would get slightly warm to the touch. I never got any further with it because I found a parts donor. I did spend several months of spare time troubleshooting this synth though.

Have fun desoldering the SDIP .070 lead pitch. This MPU is not your ordinary 64 pin DIP. I did manage to find the Hitachi MPU and a socket for it but that was a while ago.

Good luck,  Fran   

--- In vintagesynthrepair@yahoogroups.com, "hnrgaardmadsen" <helge1961@...> wrote:
>
> Hello,
> I'm currently trying to make a DX7-IID work. At power-up, all LEDs and the display lights up, and nothing more happens.
> Measuring at the MPU, it does get the 8 MHz clock signal, but it does not output the 500 KHz clock signal at pin 15. Besides, most of the adress pins (34-50) have a weird output of constantly 1.5V. - and at a few of the pins above 50, there is a slight trace of the 8 MHz clock signal. I have measured the TC40Hxxx circuits directly connected to the resonator and the crystal; they seem to work ok. And none of them run hot. As a matter of fact, nothing in the machine runs hot.
> 
> All in all, I'm suspicious that it is the MPU that has given in. Does anybody have any experience with this problem? Frankly, I hope it is something else than the MPU, it seems to be quite a job to desolder it and replace it with a new one. Any ideas will be appreciated!
> 
> Best regards,
> Helge
>