[Radio Wrangler]

OK, I've traced out the postage stamp.

It contains a quand nand device. It has +5v and ground fro the main CPU board. It has two mystery input wires one coming from the input board, one from the volume control board. The wild bit is the pin on the CPU it drives.... "INT" which seems to be usable as a plain input or for other reasons. In the manual schematic, there is a link in one of two positions, logic high or low to tell the CPU whether its in a B251 integrated amp, or in a B252 preamp. If this is so in this one, at least it's sitting in the B252 selection. The Nand gate circuit has a logical race in it, so it looks like it could make a shortish (4000 CMOS!) pulse on some occurrence between the volume and input boards. I haven't traced what these wires come from. They are hard wired, soldered, not on connectors.

I've probed the remote CPU now (keyboard removed) and its clock is running at about 4MHz.

I need to add some light pull ups to see if the keyboard is being scanned.

The IR preamp is powered from 22v via a dropper from +35v. It doesn't seem to be taking much current so it's getting about 33v.

A few electrolytics have been replaced with Japanese ones on the CPU board (and not on other boards) It seemed to have been built originally with Philips passive components.

Two capacitors, inputs to the metering seem to be loose, but they're not in an area I'd expect to put the CPUs in a sulk.

No real progress, but I'm waiting for a pattern to become clear.

Oh, and there are data and clocks coming out o the ain CPU and via the diverter switch to the display. so that path is working.

David