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Didn’t know there was a forum here, glad to find this and join you all. Hopefully someone will have a moment to take a look at what I’m experiencing here, and let me know if in fact my SAD1024A is bad. Thanks!
I recently acquired a V1/V2 DEM, I say that because the model number stamped on the board is EH1318A, not 5150B:
The problem with this unit is the flange effect is really weak, all other functions sound decent, including the Color and Range knob, even the Rate knob has a subtle effect.
I looked at the signals going in to the Balance trim with a scope, and one of my signals is missing, you can see the purple wave behaves correctly, but the yellow wave is not moving at all:
I am observing the best practices I know how for ESD when working on this, wrist strap and anti-static mat both connected to ground:
I put in new e-caps, and a socket for LM324N, and replaced LM324N with an era correct one, have not yet replaced the tantalum caps:
All of these voltage readings are with the SAD1024A chip removed from the socket.
LM324N – this chip has been replaced with a socket and NOS LM324N:
RA4588NB:
LM311N:
LMP741N:
MC14013B:
SAD1024A removed from socket, these voltages are from the socket:
Hopefully someone will be able to spot a problem, and let me know if it’s the SAD1024A. Thanks again!
Turns out my SAD1024A is not bad, I was looking at the wrong trimmer with the scope, I was looking at Bias, not Balance. Here’s both sides of the chip working together, scope on both legs of the Balance trimmer, both wave forms present and working together:
It still sounded a bit weak on the flange, so I began the alignment process.
I was able to set the Clock Rate to 35 Khz, according to the alignment document for the DEM, scope on Pin 1 of 4013B chip:
Currently waiting on a signal generator in order to finish the alignment. Really glad this SAD1024A is still good.
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