Products > Test Equipment
HP 5316A Teardown and Frequency Standard
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Kjo:
I finally got out all 3 of the HP5315A units I have and measured the behavior of the pins on J2. I have a 1928A, 1948A & 2536A. I only have schematics for the 1928A. There are certainly many revisions to the schematics over the many series. Some of the changes have to do with the battery pack I think. Nobody should plan on using an OCXO with a battery pack!
Here is how pin 1 & 6 behave across the three series I have.
1928A/1948A
pin 6 - always 10+VDC if plugged in
pin 1 - 9+ VDC if plugged in and standby/On in ON AND ONLY IN FREQ/PERIOD mode.
2536A
pin 6 - always 10+VDC if plugged in
pin 1 - 9+ VDC if plugged in and standby/On in ON but unaffected by  FREQ/PERIOD switch.

I havent yet figured out why HP used the FREQ/PERIOd switch this way in the early series yet.

This tells me that pin 1 & pin 6 are not common across the series and that for the 5315A meter the pin1 of the 004 clone should not be used.
Using pin 6 only will power the OCXO as long as the meter is plugged in.

The 5316A/B may be different. I have 2 of these to check next.
aeg:
Another gotcha with the service manuals is that the 1812A through 2032A prefixed instruments have a slide switch inside to select between the optional oscillator and the oscillator on the A1 board. The manuals for those prefixes say to flip the switch when installing a TCXO or oven option. Since prefix 2120A and above don't have this switch, the 2120A and later manuals removed this step from the installation procedure. There is no mention of the change in the backdating section of the newer manuals! The previous owner of my 5315A had field installed the TCXO option and evidently had used the new procedure on an old instrument. It was still set to use the standard oscillator, and the TCXO board was sitting uselessly inside doing nothing. I discovered this a few years after purchasing the instrument when I opened it up to calibrate it. It also had a sticker from the previous owner's in-house cal lab...

Also no mention in the manual's backdating section about the supply voltage change from 3.0V to 2.85V.
Kjo:
Yea, I have 2 5315As with that switch and an integrated crap oscillator.
After looking at my 4 5315As & 3 5316As I can say, for the series I have, DONT use pin 1 with a 5315A.
It likely doesn't matter with the 5316A/B an pin 8 is apparently unconnected. You MUST use pin 1 to get
un-switched DC power.

Another thing is that some 5315As have threaded rivets in the A1 PCB for mounting the external OSC
and others just have a gold plated #6 hole requiring removal of A1 to access the retaining nut. Not a big deal,
but a surprise none the less.

What and where are you referring to a supply voltage change from 3 to 2.85?
Kjo:
Many thanks to AMC184 back in 2014 for the original design of this circuit. It had survived many revisions and has
helped many owners to greatly improve an otherwise mediocre counter. I revised the gerbers from AMC184 recently
to allow fitment in all HP5315A/B and HP5316A/B series that I know of.

I have built 5 of these using the Morion MV85 and they work perfectly. Not willing to let a good thing pass,
I operate a small business and I decided to assemble some part kits with everything needed to repeat this by anyone with basic soldering skills.
I have 2 kits, one with and one without the MV85. (the MV85 is readily available from China on eBay or Aliexpress if you want to
wait 30-40 days!)

Everything is through-hole and assembly can be completed in 15-20 minutes.
At this time I have the kits on my website @:
https://www.hollywoodcontrols.com/phpHP/HP004OK.php

When time permits I may add them to my eBay store for those who love eBay.  :-DD
aeg:

--- Quote from: Kjo on March 09, 2023, 11:25:28 pm ---What and where are you referring to a supply voltage change from 3 to 2.85?

--- End quote ---

5315A prefix 1832A through 2032A have A1R12 factory adjusted for 3.0+-0.01V at TP+3, prefix 2120A+ changes the trimmer reference designator to A1R11 and it is set for 2.85V+-0.01V at TP+3. What difference it makes to operation, I don't know.
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