OK so an update's overdue. Had a problem with non-functioning function lamps when first powered up. The input selector switch which had it's contacts replaced with those from a AU-X7 was the first suspect even though I'd spent a lot of time on it. When I opened it up again I noticed what I hadn't seen earlier; the contact slots in the original switch rack have ribs in them which were causing excessive contact pressure/distortion. So rather than waste the new switch racks from Holland (which of course has the correct contact slots) I figured that I'd be able to make a new long rack out of the two of them. The original switch rack is a four gang whilst the AU X7 switches are three gang.Chopped the end off one of them and super glued them together, making sure the distance between slots was accurate and then filled the hollow back of the rack with Araldite to give it mechanical strength. So now I've got a selector switch with all new contacts and 4 spare contacts and there are now 7 spare original contacts, should I ever need them,for the tape function switch.
And above is the finished board, the switch in question being the lower one.
And a picture of the tone board nicely cleaned up..
The body count has gone up somewhat to a little over 100 caps, about 40 resistors (including emitter resistors), a dozen or so diodes, zeners and VD1212s. I've also replaced the digital frequency display which was a little pallid and patchy with one I got out of a T80 tuner. Big visual improvement. The channel dropping which is where I started with this project was almost certainly due to one or both of a couple problems found during the exercise; the volume control had a bad patch on the track which has cleaned up and a there was a dry solder joint in the ribbon connector between the power supply boards which was disrupting the 32V rail.
The only anomaly I've seen is that at very high power - say over 100W - with too low a signal input the unit would oscillate. This would be about 150mV rms or less; is this something I should be concerned about? The output transistors have been replaced with MJ21193/94s.
The unit power tested at 225W/230W per channel (one driven) prior to clipping.