Repair of HP 5245L Electronic Counter (with Nixie tubes!)

[Lupin III.]

Hi!

I've got an HP 5245L Electronic Counter, which no longer works as it should. Because it was standing around unused for quite some time I started it up slowly with a variac. The funny thing is, when setting the variac from something between 150V to 180V the counter works and the internal crystal reference produces it's 1MHz signal that is countable with the counter. But if I go higher, everything up to the nominal 230V the counter stops working.
I checked the voltages from the powersupply. At 150V to 180V they are of course all too low and way out of spec (still the thing works) and at 230V they are all pretty accurate and stable (also checked with oscilloscope), but the counter will NOT work.
I'm now pretty much at a loss what to do next. I have got two service manuals, but they are for later versions of the counter (for serial prefixes of 628- and 716-), while serial prefix 605- (which my counter has) should be described in the manual for serial prefixes 544-. Unfortunately the circuit boards seem to have changed quite a lot between the versions (not only the layout, but even the parts count), so except for the power supply voltages, theres was not much I could use from the newer manuals.

Can someone help me find the right service manual? Even though this device is over 50 years old, it would be a shame to scrap it. Even if it's just to save the Nixie tubes!