Vintage Synth Repair

According to Service Manual before VCO tuning D/A converter should be  
set:

- switch on with Load + Key Transpose buttons pressed, confirm that  
only Load + Key Transpose LED are on
- connect digital voltmeter to CV Out
- 1. set VR2 to get 0 V
- 2. press Play, set VR1 to get 2.75 V
- 3. press Arpeggio, set VR3 to get 2.5 V

Repeat steps 1 to 3 until all voltages are within +/- 1 mV.

For VCO Tuning you need oscilloscope as Lissajoux figures are used.

FYI:
VR1 = D/A Width
VR2 = D/A Tune
VR3 = D/A Linear
VR4 = Pulse Width
VR5 = Range Width
VR6 = VCO Width
VR7 = VCO Tune
VR8 = VCF Width
VR9 = Tune

I could find Service manual somewhere on net, try google it.

Daniel Forro


On Dec 9, 2011, at 10:20 AM, Jim Atwood wrote:

> Hi everyone,
>
> I managed to temporarily fix my power switch problem on the Roland  
> SH-101 until my replacement arrives.  I basically just cleaned it  
> and worked the kinks out by turning it on an off quite a few  
> times.  Now when I rub it, the tuning doesn't falter.  So I think  
> that part is ok for now.
>
> I then found I continued to have tuning issues which was related to  
> a missing screw for one of the PCB boards located over the VR9  
> tuning knob area.  When I tapped with a plastic screwdriver on VR1  
> and/or VR2, the tuning would suddenly flip out!  I noticed that  
> when moving the entire corner of the PCB board the tuning would  
> vary.  So I found a screw and tightened up the boards.  Amazingly  
> this seemed to have stopped my SH-101 from getting out of tune.   
> Wow!  Sensitive is the SH-101!
>
> I then found that when tuning the keyboard I was able to get the  
> lower and upper octaves in perfect tune using VR7 and VR6.   
> However, I then found that the middle 3-4 keys centering around G  
> were slightly sharp.  I couldn't figure out how to get them in tune  
> until I started fiddling with VR4.  I am not sure if that  
> specifically did the trick, but I do know that after adjusting VR4  
> and then VR7/VR6 again, the entire keyboard was back in perfect  
> tune!  Awesome.
>
> So, I'm curious. Does anyone know what VR4 does?  Has anyone  
> encountered a similar problem with the central keys not being in  
> tune after making the adjustments as instructed in the manual?  If  
> I encounter the same problem, I'll likely revisit VR4, but I  
> thought I would ask here in case someone might know specifically  
> about the problem or what VR4 does.  Thanks very much!
>
> I can now finally start jamming on the SH-101 in a more consistent  
> fashion.  They sure are fun.  Thanks again.
>
> Jim Atwood
>
>
>
> ------------------------------------
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