Biccotest T435M repair advice - FIXED

[Signal Simon]

It's a Cable Fault Locator - aka TDR. It's a CRO based unit with 7-segment LED fault location readout. It's about 1980 vintage.
I was given this by a previous employer in about 1995 as their usual calibration and repair house returned it as "Beyond Economic Repair".
There was no X deflection.
So what did it cost to get some life out of it?...
Well I bought a service manual from the manufacturer and soon determined the faulty component.... a CMOS 4069UBE IC for the trace gating!
£60 for the service manual and a few pence for the 4069!

However I did find that the Y-Amp was extremely sensitive to humidity.
I replaced the MPSA42 and MPSA92 deflection transistors at the time - there were some signs of metal migration into the transistor cases.

Within a few months of that repair I did use it to successfully locate 3 cable faults, but had many problems with the Y-deflection going off the screen.

I've kept the instrument and the original service manual and I want to get this back into a useable condition.

Any tips regarding the extreme moisture sensitivity - even breathing near the uncased unit on the bench would send the trace up and off the screen!

What's it best to clean off conformal coating with? And is the Elelectrolube APL compatible with the older stuff?

Thanks,

Simon.

[Signal Simon]

Ok well I decided to blow the cobwebs off this one and have another go.
On closer inspection, only a small area of the board is conformally coated - the CRT HV tripler area.
It wasn't that obvious, but there were signs of leakage from the "Mempac" 3.6V NiCd battery - and with the instrument being stored vertically this leakage had headed towards the deflection amplifiers.
After desoldering numerous components, I gave the PCB a good scrub with flux remover as I had found it to be very good at restoring battery contacts after leakage.
Reassembled and.... SUCCESS!
There is still a barely-perceptible decrease in X-deflection when breathing on the PCB, but no change whatsoever to the Y-deflection in either amplitude or shift.

I'm calling that one sorted.
The Mempac battery will not be getting replaced - I have no need to store a trace after the instrument is powered down.

Simon.