Oberheim Two Voice/SEM Repair & Mods

[Z]

Well I'm the lucky bastard that got the TVS that was posted a few weeks back by fellow VSE'er. A couple minutes after I switched it on it started smoking - so it's off to a tech it goes.

I don't want to have any extensive mods done to the synth, but one thing I would like it seperate audio outs for each SEM. Not sure why that wasn't done in the first place. I could also have seperate audio INs for each SEM while we're at it. These coul easily be placed in the rear of the synth with the CV/Gate jacks:


Does anyone know of any useful mods that I should consider? Does anyone recommend a specific tech for said mods? If not, where could I find schematics for a TVS-1 and or SEM to give to my tech?

Since this TVS-1 does not have the sequencer, there is a plate where mod jacks and switches could be placed:


Thanks,
Z

[Carey M]

Hi there Z! The 2-voice manuals and schematics are available at Bluesynths.

You have to be registered to download, but it's free and there is absolutely no spam, it's just a deep linking leecher precaution.

- CM

[Z]

Thanks Carey M. I'll take a look there.

Z

[minime123]

i would have the tech perform the "no smoking" mod good luck, let us know what happens. i dont think it will be that bad, 2 voices arent that complicated.
mini

[Overgear]

Hey Z! Nice acquisition! Not to worry, they are pretty easy to fix. You may have already gotten what you need from Bluesynths, here are some other sites that don't need registration...

Schematics - everything is here, even both versions of the Keyboard Electronics. If you look at the TVS Wiring Schematic, the Ext Audio In jack goes into SEM1 and the output of SEM1 splits in two. One output goes to the Output Module and the other goes into the Ext Audio In on SEM2. Interesting...

Mods - These things just beg to be modded. On the back of each SEM there are about 15 3-pin Molex (F)connectors. Most are unused. Some tap a different function on EACH PIN. The connectors are color coded. The full list is there. BTW, there are 4 Ext Audio Inputs for the VCF on one SEM. Two Molex just for that(ground are the other 2 pins.) There are pins for outputs of EACH waveform and filter mode, LFO output and trigger, 3 VCF CV inputs, and tons more...all without having to touch a soldering iron to the boards! I love this design!

I'm in the final planning stages of a breakout box for mine. Right now, I have two mod jacks - CV in to VCF(SEM2) and Ext Clock In on the MiniSeq. I might suggest Ext Mod CV inputs for the VCF and each VCO. Without the MiniSeq, there will be nothing going to the center position(Ext) of the Mod Source switches. VCF CV inputs are alway good. I also agree, it needs individual outs. Wouldn't it be great to just have left/right outs with pan knobs for each SEM....like the FVS!?

The panel where the MiniSeq would be is a great place for mod jacks. Though, you may find that isn't enough room...even with minijacks . I said I would only ever really want basic CV/Gate and VCF CV in on each SEM. Now, I'm building a box with probably 40+ jacks. I'm just sayin...It's semi-modular crack!

Not that you asked (or care)anything about the MiniSeq....
There's one on eBay right now. It's black and the reserve is probably $999, though . I didn't think I would ever really use mine. I use it a lot, now. Even more since I put in the Ext Clock In jack. I like to turn the Clock knob all the way up and see what happens. It can be musical, too . The basic functions can be done on any analog sequencer, but there are a few little things that make it unique. With two SEMs to mod and play with, though, you won't really notice its absence.

I could go on and on...I have an unhealthy relationship with my TVS. This one time I swear it called me a b***h!

I hope some of this nonsense helps.

Bill

[minime123]

We have a white faced mini sequencer we would sell for a similar price if you're interested...

[Z]

Thanks, Overgear - you rock! I didn't sign up for BlueSynths yet - been busy at work. Your links look more promising.

I think I'll pass on the sequencer for now. I'm excited to get this puppy working.

MiniMe - I remember seeing your seq on the 'bay. If I remember correctly, it's a stand alone unit. If so, how difficult is it to mount into the TVS-1 and connect to the SEMs?

Thank you all for your input.

Z

[minime123]

hi z
i dont know, i havent done it before and i personally havent been inside a minisequencer before.
mini

[Overgear]

It's super easy. I can do it and I'm an idiot. :tard:

Seriously, It's that same 3-pin Molex connecter setup. The hardest part is making the wiring harnesses to connect it to the SEMs and Keyboard Electronics. Looking at the Wiring Schematic, you would need four of the six wiring harnesses. Since the KeyElecs go straight to the SEMs in yours and the MiniSeq would be installed in between these(literally AND schematically), common sense(not mine, someone else's) tells me you have enough length on those two harnesses. If you look at the bottom of the SEM mods page, there is a link to the mod info for the MiniSeq, as well.

Of the remaining four, only two require all 3 pins be used and that's only on one side of the harness. Also, since all(or most) of the molex connectors on the SEM-based gear are female, all you will need on some are the pins. What do I mean? My filter CV jack is goes: minijack - wire - molex pin. No connector. When I installed it, I popped out one of the jack covers on the back, mounted the jack and stuck that pin into H1 on the gray molex connector on SEM2. That's another thing! Not only are the molex connectors color coded, they are letter coded and each pin is numbered. I don't fully understand schematics, but these I stare at a lot! The insides (<--nice!) almost make me as giddy as playing it. Look over the Wiring Harness Schematic while looking at the SEM mods page. It helps to make the correlation between the modules.

If you have ever worked on your own PCs, installing any module in an SEM-based instrument is like plugging your power supply into the motherboard and other system components. In fact, it's not like, it is the same!

BTW, the power supply harness on the Miniseq should be able to be used, as well. The TVS should have an open connector. Those are 4-pin Molex.

I love these things!

Do it!

[Chevytraveller]

Hi..

Just resurrecting this thread as there is some great info here but sadly the links are dead.. does anyone happen to have this info that would be willing to share?..

[Rbh]

I checked the link and most are abandoned, the Mods link ( http://www.angelfire.com/music2/theanal ... e/sem1.htm ) still worked and you can do a generic google search for schematics.

Here's a link to a repair thread for a 4 voice that you may have seen before. It seems I'm getting a error - but hopefully you can link to this thread through google ( https://www.google.com/?gws_rd=ssl#q=hi ... ice+repair )

[Chevytraveller]

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Great stuff, thanks..

S.

[solitud]

Is there a service manual / process how to calibrate the Miniseq? It has three trimmers on the back but not sure what they do.