R2008 AUDIO SYNTHESIZER (A6) MIC IDC Problem

This document is written in English for overseas OMs.   -DS1ORJ- 

 

My R2008 is having problems with its mic input.
I've been tracking it for a long time.
The cause was damage to the IDC(Instantaneous Deviation Control) circuit of the A6 module.

 

Bottom left of the A6 module.

This blue hybrid IC is not working.

 

 

U45 IDC, it simply looks like a preamplifier connected to the mic input.

I melted the surface with acetone and magnified it under a microscope.

 

The bonding wire looked okay, but it is measured that the trace on the VCC(+) side is broken.

Patented and no internal schematics provided.

 

I saw the service monitor schematic made later(R-2200, R-2400).  There I saw the IDC circuit.

The IDC circuit is in the FRONT PANEL INTERFACE BOARD (A14) of the R2200A schematic.

 

 

It is probably made of 3 low noise OPAMPs, which can be replaced by the TL074.

yes i made it.

 

 

 

 

Its amplification was low. So the R51 4.99K resistor at the input was replaced with 1K.

(5 times higher than the original design.)

 

It seems to provide the ability to adjust peak control and frequency response.
However, no response measurements or simulations were performed.

 

Circuit replacement complete. It works fine.

 

If you have any questions, please send an email to codeart74@daum.net.