Sunday, 2 July 2017

Paperface Serge - Negative Slew restoration

Serge  Negative Slew restoration.
These are some notes for repairing a old Negative Slew.

The main panel is here 

The board is marked R9
This is the lower section of the PCB.
The upper section works.
According to Ken Stone's site there are two problems with this.
It's missing one trace and a 4.7k resistor.
I've marked the missing trace in orange.

Also marked the missing 4.7k resistor in orange.

4.7K resistor added.
I removed the 3900 opamp. lots of corrosion in the socket.
Replaced & it works.
Thanks Ken

2. CGS
3. Muffs
The 1973 PCB used +12, +6, -12 & ground.
The 1975 PCB used +/-12 V & ground.
So I'm guessing this is a 1975 PCB  as it uses +/-12 & 0V unless it has a on board 6V regulator.

The module uses two ICs
LM3900. It's a quad op amp

 Ground at pin 7, power is pin 14.

This is a transistor array.
It consists of five general purpose silicon NPN transistors. Two of the transistors are internally connected to form a differentially-connected pair.  

PCB connections:
A = input (1)
B = output (1)
C = VC (1)
D = pulse out (1)
E = input (2)
F = output (2)
G = VC (2)
H = pulse out (2)
U = not used (0v)
W = 0v
X = +12v
Y = +6v
Z = -12v

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