Trueman 1966 - Schematic (?)

[drdn0]

Howdy,

Thought I'd actually take the time to fix the Trueman 1966 I picked up for next to nothing. First step was creating a schematic. While it's sort of similar to the Coloursound 1966, there's a lot more going on here. The 20k trimpot between GND and 9v is a bit confusing - is this just to provide some sort of stability while running PNP's on a positive supply?

[PRR]

IMHO, there HAS to be an impedance between Q1-C and GND, to divert signal into RV1 etc. Or RV1 is that impedance but not connected as drawn.

Sure looks like a FuzzFace with odd grounding. It is very difficult to dope-out a re-grounded plan because the mind leaps to what it expects. (The time I had a radio station off the air for a month because the console was first of a new reverse-polarity plan and I was blind to the way it was really powered.)

[drdn0]

IMHO, there HAS to be an impedance between Q1-C and GND, to divert signal into RV1 etc. Or RV1 is that impedance but not connected as drawn.

Sure looks like a FuzzFace with odd grounding. It is very difficult to dope-out a re-grounded plan because the mind leaps to what it expects. (The time I had a radio station off the air for a month because the console was first of a new reverse-polarity plan and I was blind to the way it was really powered.)

All the trimpots are little micro SMD ones (odd choice), and absolutely impossible to see what traces are doing near them - TRIM2 might be a voltage divider to ground, but I can't see what's going on under them. I'll get to a hot air station on the weekend and see if I can pull them off.

I did get TRIM1 off with a bit of difficulty, but oddly enough it reads open on my meter across all terminals.

[amptramp]

My suspicion is that TRIM1 was supposed to go between the collector of Q1 and ground.

[Rob Strand]

hought I'd actually take the time to fix the Trueman 1966 I picked up for next to nothing. First step was creating a schematic. While it's sort of similar to the Coloursound 1966, there's a lot more going on here. The 20k trimpot between GND and 9v is a bit confusing - is this just to provide some sort of stability while running PNP's on a positive supply?

I'm not going to trace it but this is a rough trace I did a while back.
It has not been checked. I just went over a pcb pic one day and left it.
As such I've made no attempt to have the same designators as your schematic,
nor have I made any attempt revisit my trace by using your schematic to fix my trace

The main reason I'm posting this is I'm pretty sure the circuit on
Q1.c and Q2.b  are three pots arranged so one of the trimpots
sets the minimum resistance and one sets the maximum resistance.



I thought the supply adjustment was just a series resistor.  However, I did not trace out
the LED circuit to see if it was post or pre the supply series resistor.

If this helps, all good.  If not just ignore it.

[drdn0]

hought I'd actually take the time to fix the Trueman 1966 I picked up for next to nothing. First step was creating a schematic. While it's sort of similar to the Coloursound 1966, there's a lot more going on here. The 20k trimpot between GND and 9v is a bit confusing - is this just to provide some sort of stability while running PNP's on a positive supply?

I'm not going to trace it but this is a rough trace I did a while back.
It has not been checked. I just went over a pcb pic one day and left it.
As such I've made no attempt to have the same designators as your schematic,
nor have I made any attempt revisit my trace by using your schematic to fix my trace

The main reason I'm posting this is I'm pretty sure the circuit on
Q1.c and Q2.b  are three pots arranged so one of the trimpots
sets the minimum resistance and one sets the maximum resistance.



I thought the supply adjustment was just a series resistor.  However, I did not trace out
the LED circuit to see if it was post or pre the supply series resistor.

If this helps, all good.  If not just ignore it.

It looks like there are a number of different PCB's floating around - the other one I have seen posted was bare copper and appears to be TOTALLY different values on components. I also absolutely need to clean it properly with isopropyl as it was absolutely filthy (plus now my Sharpie is on it)