I now have it working properly, but still don¡¯t know what the original problem was. Maybe resocketing transistors and the CRT did some good. The Y output amplifier was bad, but I found a new one on eBay. After getting a decent trace, the Y attenuators were not working properly. I brushed the leaf contacts with IPA, removed the attenuator blocks one by one, cleaned the pins, wiped them with IPA and plugged them back in. The AC-GND-DC switches also needed similar treatment. I have rational progression in Y gain on both, so all in all I think it had been in storage a long time and many contacts had gone bad or intermittent. The X position occasionally wanders to the right, but comes back after a while, maybe another poor contact to track down.
Thanks to everyone for useful advice.
Simon
