Vintage Synth Explorer Forums

I got a Multivox MX 3000 from ebay and it seems to have a short circuit between the positive supply and GND. After disconnecting some cables the short circuit was gone and I couldn't measure it on any of the boards, so I guess it must be a wiring issue. I've got a service manual from musicparts.com, but it only has schematics of the boards.

Does anyone have a same/similar issue with this synth? Could someone, who has a working MX 3000 share a picture of the wiring connection under the front panel and behind the main boards and also on the jacks.

It works!

I checked all the connections according to schematics, disassembled it and put together again. Except cleaning some dirt off the PCBs in the bottom and using plastic washers to avoid contact between PCBs and screws I didn't do anything. Now only the VCF of the poly section is silent. I guess it is a faulty ca3046 transistor array IC. The keyboard contacts may need some cleaning too.

All I read about Multivox' build quality seems to be true. PCBs have soldering tin spills everywhere and the soldering quality is quite poor. It looks like the PCB layout was done before any prototype was built, so during the assembly process they needed to scratch off some leads, use wires or solder some components directly to each other. Luckily the hand drawn schematics I got seem to correspond with the the assembly very well.

It was a good experience to study this synth: all discrete components, every section of the analog synth (VCO, LFO, VCF, EG) is build on a separate PCB. It seems the synth I got has never been serviced before: all the screws still had their original sealings. The condition is surprisingly good for its age. Even the sliders don't show any signs of wear.

I've had one of these in my attic for 15 years. Just pulled it out to test. it definitely needs some work. At first it didn't make any sound, and the presets lights were hard. I gave it a firm smack on the top and it came back to life. Only output 2 is working. there's some crackling and such when turning the rotor on and off and a few other anomalies and instabilities. At times it can be fairly stable, I'm not sure if it's worth paying someone to work on it, but i'm evaluating

Hi miaomiao!
I just picked one in poor electronic condition (but mint looking).
I'll have to work hard on it to be able to make music with.

Do you still have schematics?
Perhaps we could make a deal (I have many other schematics here)?

Thanks a lot.
Ory

Not sure my first attempt worked so I'll post again, you got the MX3000 in Paris I assume?

Schematics here: https://we.tl/t-ZEvQnaMtjt

These are not great schematics but the only ones out there to my knowledge.

Woaw, instant time travel: Is it Christmas again?!!!
THANK YOU SO MUCH PUDDY B!
What an unexpected surprise!
I had no hope at all.
Yes, this one was in Paris. I found it on Audiofanzine ads, and a friend of mines who was travelling from Paris to somewhere here grabbed it for me.
I'll visit him next Saturday, and take the synth (and we'll have a look into it together).
That friend owns one of the mega-big and mega-rare Korg PS3300 still working.
We'll have fun on it (what a chance!), while drinking some good beers!

Well, this is my best WE of the year, I assume!

(Well, I perfectly got whole manual, you don't need to post it again.)
Thank you thank you thank you again!

Hi there... me again. I worked hard on my poor old MX3000.
I solved:
- D# bass sound continuously sounding (2 transitors short-circuited on board 91615 #2)
- Polysynth filter muted (2 2SC1740 appaired transistors dead)
- Channel 1, 2 & 3 outputs repaired (1 wire cut, 1 short-circuited capacitor, and 1 VERY VERY dirty jack )
- CH 2 FX Ensemble & FullRotor output muted (volume slider cursor allmost broken). Hey dudes, those both things sound so nice!

Remains unsolved (for now):
- CH 1 bass portamento time doesn't vary according to the TIME slider setting. SLIDER itself or jrc 4558#1...
-CH 3 Solo Synth VCF cutoff doesen't operate at all. I CAN'T trace the CV signal path from cutoff slider (works correctly): BEFORE the 1M resistor, the CV range is 0/+13v depending on the cursor's position... And AFTER that dammned 1M resistor, 0V. Allways!!! I replaced that resistor, but nothing's better... But I'll find.

-Can't transpose the PolySynth octave up/down using the GLIDE selector. It worked ONE time, the first day I tried it, then nevermore...
However, the GLIDE itself doesn't operate either, while it shares the same time factor slider with portamento, that works perfectly. Using the foot switch rear input, the TRANSPOSE toggles perfectly well...
I assume everything leads to that 91611 MOP-1 master oscillator module/board (bottom left corner in the synth's case, pin #5), THE ONLY ONE THAT IS MISSING ON PREVIOUS SCHEMATICS...
I searched using MULTIVOX, PULSER, FIRSTMAN, and HILLWOOD (some boards inside marked after those brands), but couldn't find that schematic...
Does anyone know where to find it?...

Hmmm... Well, I think I'll have to retro-ingeneer that board by myself.
Will draw schematics and post them on the dedicated topic.

oryjen wrote: ↑

Wed Jan 29, 2020 9:22 am

Hi miaomiao!
I just picked one in poor electronic condition (but mint looking).
I'll have to work hard on it to be able to make music with.

Do you still have schematics?
Perhaps we could make a deal (I have many other schematics here)?

Thanks a lot.
Ory

hi oryjen, you got PM
sorry, I haven't checked this forum in a while

Hi guys, i have a mx-3000, i restored full on ch2 and ch3, but i have some problems on CH1, i don't undenstand where is bass cvgate , in addition it's modified about IC over bass portamento switch, anyone have idea ? please anyone can post a photo of this parts of anyone have a decent schematics ?
thanks
Regards
Mirco

Hi again, hope this is resolved and you got it up to snuff, these are beautiful machines!
This is related to the last comment at the bottom of this topic.
My repair guy has got mine up and working very well, except for the bass section, where the bass board looks different to the schematics, like not similar at all, do you have any pics of the bass board you could send me, if you haven't closed it up already?

Well, I try to post here some commentated pics of mine:





Got it?

I also have a mx3000 and need info on the adjustment procedure...?

Does anybody have user manual for mx3000 ?

https://we.tl/t-ZEvQnaMtjt

This includes SERVICE and USER's manuals.