Bell ADT Automatic Double Tracker trace [schematic]

[krystal]

I thought this might be of interest. It's a kind of modulated doubling delay.
This particular unit is quite distressed. I've traced it to help debug it.
Switching and power are not shown. It has it's own plug, and i couldn't be bothered to follow the wires around a transformer and bridge rectifier etc. There's a couple of regulators for +15V and -12V.
I'm not very experienced with this stuff, so please take it all with a grain of salt.

It seems like a previous owner tried some repairs/maintenance (like that Mod pot that's been replaced)
So far i've replaced a couple of electrolytics, a tropical fish and both cmos ICs that were damaged.
I've found some resistors to be way off spec and will be replacing those shortly.
Some of the tropical fish have some small cracks on their surface, should i be replacing those too?

I've got it running but not getting any modulation so far. The Delay and Dev(iation ?) seem to be working.
Probing indicates that U6 (on my schematic) is oscillating but i can't hear it at all when probing around the 4046.
R50 & R51 are two of the resistors that need replacing (R51 is that big resistor near the 4046 that seems to have been previously replaced)

I can upload/take more pictures if necessary.

[Dirk_Hendrik]

Great work Krystal!!