Synth-DIY Yahoo! Groups Archives

Thread

MG adjustment on KLM-367a Clone

2018-09-20 by golbicali@yahoo.com

After a problem with D/A adjustment now solved i come with a new problem:

When doing MG adjustment

A)i'm not able to get a larger vpp than 0,780v.

B)and in the second step, at max speed the frequency is really slower than 50hz with VR5 all the way up. It is almost the same using others LM13700 that i had.

Should i change some resistance values? If yes, should i increase or decrease resistor values to get a faster MG speed?

or maybe there is a fault on the board?

Thanks

Re: MG adjustment on KLM-367a Clone

2018-09-26 by golbicali@yahoo.com

On the KLM-367a clone board the MG Vpp adjustment has been now successful. (problem was with R56 that was 0,125W in staid of 0,250W )

But the MG frequency adjustment is still not good.

Service manual suggest to replace R52 if 50hz can not be obtained. Results are almost the same using new LM13700 or the LM13600 from the original KLM board.

-The most faster frequency i can get is around 8hz with a 12.1K resistor on R52 ( originally R52 is 150ohm ! ).

-If i replace R52 with a 15K it stop oscillating.

So, should i find a resistor between 15K and 12.1K to obtain a 50hz frequency?

Do you thing there is a problem elsewhere in the MG circuitry where i should look at?

I hope that someone could help me.

Thanks.

Re: [PolySix] Re: MG adjustment on KLM-367a Clone

2018-09-26 by Bob Grieb

Clearly there is a problem with some other part of the MG circuit if
you have increased R52 from 150 to 12K and the max frequency is still
1/6 of what it should be. I would look at Q3/VR5, R55, 68, 69, TH1
as these control the current into IC21 which seems to be the problem.
I would put R52 back to 150 ohms and look for the real problem.

Bob