HP 5316A Teardown and Frequency Standard

[pizzigri]

Hello to everyone in the thread! And what a great thread this is. There’s a 5316A coming my way, and I just was looking around for a tear down to see what to expect and maybe some repair advice and bam! The OCXO mod....So I’m hooked, is anyone willing to part with a spare board? I’m located in Italy....

[reddish75]

I have a 5316A which hopefully works properly but have a question, how do you display the frequency inputted on channel B?

[David Hess]

I have a 5316A which hopefully works properly but have a question, how do you display the frequency inputted on channel B?

I do not think you can.  The A input can be routed to both the A and B channels using the "SEP/COM A" button.

[W8RLC]

I know you specifically built this TXCO for use with the HP5316A. I have an HP5314A and was wondering if this replacement could be adapted for use with it.

[amc184]

I don't think this board will work well with an HP 5314A.  Unlike the 5416A, 5416B and 5415A it does not include the same plug in position for a frequency standard.  I do see a position for a TCXO option on the rear PCB of the 5314A, so it looks like there may be a way to upgrade it, but not using the same PCB as the others.

You could look at making an option for the 5314A, but it might be easier just to get a 5416A instead.  They regularly sell for less than USD40, and have a better feature set anyway.

[beastor]

Picked up a 5316A with the 1GHz C input from eBay.   Checked it against my Louis Scully GPSDO and it was out by 23Hz, but the adjustment screw was already at the maximum, so I decided to use the board from amc - it works a treat!

Even though mine didn't have the 'Option 4' marked on the rear, it looks like it had that retrofitted afterwards?  Semi-officially?

Picture included below of the board I replaced.

Thanks again amc!

[alitronix]

Hello , I have the HP 5315 A model unit with fried transformer ,
can anybody tell me the transformer deliver 2x8 or 2x7 AC V? (on 5315A model)
I can't find it on manual (sorry in case if is there the value and  i miss it  ) .

If I put 2x9V or 2 x10V it is ok? (this what I have ).
Thanks in advance.

[bdunham7]

Hello , I have the HP 5315 A model unit with fried transformer ,
can anybody tell me the transformer deliver 2x8 or 2x7 AC V? (on 5315A model)
I can't find it on manual (sorry in case if is there the value and  i miss it  ) .

If I put 2x9V or 2 x10V it is ok? (this what I have ).
Thanks in advance.

The unregulated DC supplies are +/- 7.5V and they have the 4-way line input selection (100/120/220/240) which sort of indicates to me that they anticipate that unregulated supply will be within 10% or so of nominal.  Increasing the transformer voltage would add heat stress to the regulators and I don't know how much they can tolerate.

I measured the transformer output on my 5316B for you to compare to (it should be the same circuit) and with the unit off but plugged in--which means the unregulated DC bus is powered and on mine, the OCXO is warm--I get 15.4VAC.  With the unit powered on I get 14.6VAC.  So I'm guessing that an appropriate transformer would be 7.2V nominal and about 8.0V no-load on each winding if you were using a 2-winding transformer in a CT configuration.  9 or 10VAC would probably work at first, but may burn something up in short order.

[alitronix]

Thank you for support ,
It is impossible to find here in Europe a 2X7 VAC transformer at a reasonable price...
I just find on eBay a 2x8 VAC ,is not the same old stile format but I will be able to put in with no hardware changes ,
I believe will be OK for the moment and meantime I will search for a original one or something very similar.

I powered it up with external AC variable power supply just for test and seems to work fine.

Thank you for help, much more clear now.

[hvontres]

Hi, I was wondering if anybody had any spare PCB's for the OCXO option? I will be getting a 5316A soon and would like to install one. if not, I'll go and get some made at PCB way.

[softfoot]

A very interesting thread - I wonder if anyone in the UK has a spare OCXO board for the 5316A ??
Please contact me offline if so.
Many thanks,
Dave

[hvontres]

Hi, I was wondering if anybody had any spare PCB's for the OCXO option? I will be getting a 5316A soon and would like to install one. if not, I'll go and get some made at PCB way.

I have three extra PCB's in the US if anyone is interested.

[hvontres]

Finally got my board working and installed. Turns out a lot of cheap LM317 Voltage regs use the LM317-L die internally, so even though they look like a full fleged 1.5A regulator, they crap out at 200ma. I almost returned my two OCXOs since they really don't run well on 2.5V instead of 5V. Once I put in a nice vintage LM317-T, the board has been working great.

[Kjo]

I have collected maybe 6 versions of the 5315A/B 5316A/B over the years. The earliest 15A is series 1928A (1978-78), but there are 4-5 series even older. None of these had an option 004 OCXO as far as I can determine. Up through the 1928A at least, the basic 10Mhz osc was on main A1 PCB. And the 6pin jack was used for a TCXO.
The series 2xxxA look to have eliminated the A1 osc for a basic, TCXO, OCXO plugin oscillator. I think this is important because pin 6 of J2 is used differently in various 5315A/B as well as in the 5316 series.

Unfortunately, only the 5315 series 1824 service manual in the wild has complete schematics. (Although I have an OEM manual for the 1928A series.) The bottom line I am getting at is that the amc184 PCB gerbers tie pin 1 & 6 together and this could be a problem for some 5315 PCBs. It is best, I think, to not include a pin 6 when working with a 5315.
Feedback desired.

[Kjo]

Another thing that bugs me about equipment manuals on the internet is the abundance of incomplete pdf files. There are dozens of HP5315 manuals missing section 8 and all the schematics. There also seems to be a level of ignorance in that the series prefix releases in this type of equipment. Manuals that match the series one has in hand are indispensable.
Unfortunately, keysight only published a very early 1978 complete manual. There were more than a dozen series after that. I would like to see schematics from a 21xxA series.

[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. 

[aeg]

What and where are you referring to a supply voltage change from 3 to 2.85?

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.

[Kjo]

5315A prefix 1832A through 2032A have A1R12 factory adjusted for 3.0

Interesting, as that is the termination/reference bias source for the MRC high speed signals from the channel input conditioners.
My 1928A service manual has A1R12 (287 ohm) in the collector of Q2 Colpitts onboard crystal oscillator. R15 is the adjustment pot for the 3VDC
supply. I think the onboard oscillator went away with the switch in series 2XXX+.
I wonder if the part numbers for the MRC are different. I have only ever seen one part number.

[aeg]

Oh, there's an inconsistency in the 1832A manual. The reference designators shown in the adjustments section don't jive with those in the schematic. There are no reference designators printed on the PCB itself.

The MRC is 1820-2139 in the 1832A parts list, but it changes to 1820-2312 in the 2120A parts list.

[Kjo]

Interesting,,,
I've only ever seen MRC 1820-2312 labeled parts. My earliest meter is a 1928A series.
In the late 1970 this MRC may have been a challenge for HP to mfgr with yield. It was a bipolar
chip with everything from ECL to IIL inside.

My paper manual 1928A (1979) has those grey-over photos with part reference designators printed over
certain parts.

Double check your parts list though. My list says 1820-2312 for HP part number (col 2) but 1820-2139 for Mfgr part number (Col last).
It lists HP (28480) as Mfgr. Dont know why HP would use 2 different numbers for same part, but # on package
has seemed always 1820-2312.

[aeg]

1832A and 2120A series parts lists have matching "HP" and "manufacturer" part numbers. I guess for 1928A they decided to compromise. 1820-2139 labeled parts do exist in the wild: https://www.flickr.com/photos/anachrocomputer/43289590070 (not my photo). 2120A manual also has modification notes for substituting 1820-2312 for 1820-2139 in early units - see one of the 05315-90021 scans, p. 117 or p. 118 depending which scan you have.

[Kjo]

@aeg
Thanks for that confirmation photo!