Another one of the EIP 545A counters, that are for some reason very frequently seen at my workshop. The reason for this instrument being here on the bench is simply for the fact that I found it on ebay, for a very reasonable price, non-working, but with the 04 OCXO option.
The option 04 provides 10^-9 level frequency stability, per day.
The actual OCXO unit is an Ovenaire 49-38c model 10 MHz oscillator. Very similar OCXOs are used in various HP equipment of the time.
The first item to fix – the very noisy fan. An ETRI model 126-LF-182. Fortunately, a very common 115 V model.
Replacing fans, you can’t just go for the flow rating, but you also need to consider flow direction, static pressure (mostly related to the blade shape and RPM), noise level, lifetime, and bearing type (ball bearing).
Found a very similar NMB fan, which is available from new production, at a reasonable price.
For comparison, the ETRI data put into the NMB pressure vs. flow characteristics, as red dots. Indeed, quite similar.
When changing the cable, from the old to the new fan (EIP uses a special connector, so I needed to re-use the old connector) – seems EIP didn’t trust their crimping, the cable was additionally soldered to the crimp pin.
The new fan installed, make sure to use some insulation tubing (not present in all EIP counters, but was present in this one, and a good idea, because the fan cable runs directly underneath the top cover, and over time, could be damage and expose mains voltage to the case (not a good thing!).
Next fix – a broken tantalum on the front panel (capacitor was OK, but one wire broken off) – fortunately, it could be soldered from the top, because disassembling the from panel is quite a time consuming task.
Finally, all these things fixed, but still a non-working EIP. It would not even count low frequency, or show any reaction on the display. All voltages OK. That’s strange – most likely something with the CPU, data bus, or similar. So, swapped the main CPU/control board with a know-good assembly, and the EIP came back to life. After some checking and probing, found one EPROM that had corrupted data – no wonder it didn’t start up.
While cleaning the power supply (removed the card from the main board), another issue showed up: EIP didn’t use sufficient thermal grease to make good contact of the assembly cage (used as a heat sink), and the heat conductor of the power supply assembly. All screws were tight, but no contact.
So I cleaned up everything, and added some more generous amounts of a good thermal compound.
This is the top view: you can see the OCXO auxiliary power supply to the left, and the OCXO in the right upper corner.
Also quite interesting, this unit has seen some pretty famous owners, including, Bell Labs, AmerSatCo, and Verestar, Inc. – probably, it has seen good use, also judging from the noise fan, which has 50 khours+ lifetime.
One all had been fixed and confirmed running, I could not resist to also add the 02 option Power Meter Upgrade to this unit, it is in the end just few eproms, and some additional parts for the A107 assembly.
… counting at 10 GHz, and showing the power.