Vintage Synth Explorer Forums

I just got a busted jx3p, recapped the power supply and got it to turn on but all it does when powered on is emit a long drone from the headphone output and nothing else, the keys do nothing but the surface panel buttons can do some things- chorus works but not the lfo switch and i can change the banks but it only slightly alters the tone.. any ideas where i can look for a solution?

Are all analog voltage lines +15V, -15V present on the PSU ?

Yekuku wrote: ↑

Sat Dec 12, 2020 11:43 pm

Are all analog voltage lines +15V, -15V present on the PSU ?

yep it seems to be nothing wrong with the power supply i wonder if one of the voices has an issue with the envelope making the constant drone, but i cant tell what is making none of the notes play on the keyboard and dont really have experience tracing down problems with the digital side of the synth...i figure i ll have to socket and swap/test ics after researching but im not sure which ones to start with

weird i double checked and on connector 1 from the psu im getting 15 and 5 within range but -15 is reading as +1v?

+1 V is a bit on the high side but it should not cause this.
What happens when you connect an external midi keyboard?
If the problem was on the amplifier envelope, it should reproduce pitch intervals.
To me it sounds like you have a problem on the digital part of the DCO or the keyboards key assigner.

cosmolac wrote: ↑

Fri Dec 18, 2020 1:28 pm

weird i double checked and on connector 1 from the psu im getting 15 and 5 within range but -15 is reading as +1v?

Let's get that negative power rail figured out. Does it still read +1 with all the connectors going to the other boards pulled?

DJFIX wrote: ↑

Sat Dec 19, 2020 8:59 pm

cosmolac wrote: ↑

Fri Dec 18, 2020 1:28 pm

weird i double checked and on connector 1 from the psu im getting 15 and 5 within range but -15 is reading as +1v?

Let's get that negative power rail figured out. Does it still read +1 with all the connectors going to the other boards pulled?

nothing with midi, pulling the other connectors +5 is okay but + and - 15 are now 20v, one connectors -15 just cycles through +0-8 on the multimeter for some reason
im using ref gnd from connector 1 but theres also a and d ground is there a better test point to measure that im missing?

The +15V rail reading 20V without anything connected is probably OK (as long as it dips back down to 15 under load).

The -15V rail readings you mentioned are definitely off. The power supply should not be reconnected to the rest of the unit until you get that part sorted. Check out Q2. I have also seen M5230 regulators go bad in other equipment. If Q2 checks out, I would do the 5230 next.

A misbehaving power rail could certainly cause a lot of trouble.