OK, all was going well, then....
As previously described, the battery is replaced, as is the display tube. I started to play with it to make some meaningful measurements.
Until yesterday, it all worked fine, then, towards the end of the day, I discovered that the Signal Generator was outputting a signal about 20dBm low (when compared with another signal generator). I used a ham radio transceiver - the other signal generator reported 12dB SINAD about right for the specifications (~-115dBm), the Anritsu was about 20dBm low (~-93dBm).
Today, it's nearly 100dbm out (12dB SINAD at ~-15dBm) - the spectrum analyser only shows a very strong signal and the TX power measurement isn't reading anything. The readings are the same when when using the AUX or the MAIN inputs. There's been no significant power presented to either input / output.
My only concern is that whilst replacing the display tube, I disconnected an SMA connector from the attenuator unit at the underside front and this connector doesn't feel properly seated. (Unit marked 339H40998A D59090 A01). I can't get it to mate fully. Could this be the problem?
I've checked my leads / adaptors and cross checked that the radio still responds to a reading of -115dBm from the other Signal Generator.
Any pointers as to where to start diagnosis, please?
Thanks
John
(I have a copy of the MT8802A Service Manual)