hp 5385A Frequency Counter

[xrunner]

I already have a 5384A which has a range of 10 Hz to 225 MHz. Member bd139 recently got a 5384A and is putting in his own OCXO -

https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3531098/#msg3531098

This kindof got me thinking about getting the 5385A. The 5385A  has a range of 10 Hz to 1 GHz.
I hadn't got any new gear recently but I ran across an hp 5385A frequency counter last week, so I couldn't resist. I'm just going to document any issues I run across in the checkout. There's always something with these older units, and I expect this to be no different. The attached picture is as it was received yesterday. Upon first turn-on, it seems to be working well, but I know it'll have a curve ball to throw at me. They always do. I will have more pictures in the following days.

Thanks for reading along.

[xrunner]

Take-it-apart pics.

Remove the feet and remove four long screws. Oh yea, the feet on this one didn't run away over the years like many other hp gear (or they are replacements ... but they look original). The screws - If anyone reading along out there wants to get into this older hp gear but isn't familiar, here's a factoid. Many of the fasteners used look like Phillips screws, but are in fact Pozidriv screws -

https://www.albanycountyfasteners.com/blog/what-is-pozidriv-is-it-different-from-phillips/

Obtain the correct driver! 

Remove sticky tape strips from each side at the front. Pull top off.

The top and bottom of the plastic case has an rfi shield coating applied, has good conductivity. Worked on the red sharpie writing on the front panel, got it all off. Front panel looks OK with some minor scratches - to be expected. Applied goo-gone to cal stickers. Expecting to perform the calibration steps in the manual, several adjustments other than the obvious one (TCXO reference cal).

Will inspect the boards and operation in detail next.

[Miti]

That is a good instrument but the TCXO is junk. You can install an OCXO, see here:
https://www.eevblog.com/forum/testgear/hp5385a-ocxo-timebase/msg1802765/#msg1802765
I will post the Gerber files soon.

[xrunner]

That is a good instrument but the TCXO is junk. You can install an OCXO, see here ...

Don't need an OCXO because I'm always going to use it with a GPSDO external reference. 

[xrunner]

After removing the GPIB board for pics, the rear panel seemed too loose. The only thing left holding the rear panel was the ext. ref. BNC which was soldered to the main board. I inspected this and found the BNC connector support pins that are soldered to ground had a cracked solder joint around each one.

This is an easy fix. However, I wanted to make sure all the static forces were in place before I soldered them, so there wouldn't be any new twisting force on the pins after the repair. The forces pushing or pulling on the rear panel were the GPIB board which is screwed to the back, this having an upright plastic standoff inserted at the rear. Also the top of the case, which has channels that the rear panel has to fit in, can cause a force to be exerted. After all the alignment was situated by having these parts in place, I re-soldered the pins.

[xrunner]

When selecting the gate times, the 1.0 s button didn't seem to be operating. Upon further examination, when pushed hard, it did finally go to a 1.0 s gate. Obvious issue - a cleaning was needed. Since the entire panel will be exposed, they will all be cleaned, I was thinking. But it wasn't to be.

The button assembly isn't meant to come apart. They decided that it would never need to, and so used metal clips that do not come off (without breaking pins). After considering all the options, and test-prying the back, I determined a way to at least clean the stubborn button.

I used a material that was part of a new clean absorbent pad meant to soak up spilled oil. Seems like an odd choice, but it had a texture that I thought would clean the carbon pad and still be able to get into the very thin opening. Once I pried up the back plastic as far as I dared, I stuck in the material. Each time I pulled it out I pressed the button down against it. I did this about 6 times and put the board back to check the button sensitivity. After a few more cleanings, the button had returned to normal. Since the back was pried up, I cleaned a few more buttons around the area the same way.

Whew! 

[jerryk1234]

I wonder if it would be possible to sneak in a backlight for the display?  Maybe some LEDs meant for dollhouses?  Those
are basically surface mount LEDs with leads soldered on.  You have to see them to understand just how small they are.