HP 53131A Teardown and Spillage Clean-Up

In this video I teardown a HP 53131A frequency counter and find a spillage that I need to clean up. I also look at the power supply and the ridiculous design of an always-on Switchmode PSU and very annoying running fan, when when the instrument is turned off

[gerrysweeney]

Hi Mal, I just got hold of three more of these counters and they have the same problem and it looks like you are spot on. I guess my first counter the molten rubber made its way out of the counter and not in!

[gerrysweeney]

Hi Cip, thanks for your comments, I am glad you find the video useful. Gerry

[gerrysweeney]

I done some further testing this morning and it would appear that the counter is working a lot better than before, its happily triggering at 50mv so I guess the cleaning has helped after all....

[iknowsstuff]

lots of lab instruments keep fans running when they are off, the reason is likely to even out static charges that could mess with readings when the device is turned on or so i have heard

[helmetdump]

Hi, I have one of these counters with damaged front panel BNC connectors. Would you happen to know what the amphenol part number for the BNC connectors is?

[gerrysweeney]

That would make sense, thanks for clarifying. Gerry

[AbdullahKahramanPhD]

Please do the mod and a mod video, I am looking forward to it! :)

[Make_it_to]

hi, Gerry, i must say, i am hard to be impressed, but u made it, thank you to share with as your knowledge, i just subscribed and i will consider you like my teacher... well.. at last for a while ... i learn very quick.. thx again. Cip from Italy

[gerrysweeney]

Yeah it would make sense of the OCXO *but* according to the schematic, the only supplies going to the OCXO option board are switched (i.e. after the power is turned on), so I am not sure. I too like the VFD's, they are a big part of what makes them desirable.

[gerrysweeney]

Just checked this again and actually the unswitched +/-12v are going to the OCXO connector, not sure why I missed that in the schematic before. That still leaves the mystery -9V supply??

[gerrysweeney]

Not sure really, it does not seem to show up as being connected to anything on the schematic so its anyones guess....Gerry

[KeenanTims]

- that 9V is weird. the troubleshooting steps in the manual don't even bother to have you test it. you'd think they'd have a custom PSU for this, but maybe it's an OTS unit with an extra rail they aren't using? or maybe it's used for one of the options?
- OCXO option is likely the reason for the PSU fan, a few watts at least to keep the osc warm while in standby

nice teardown/repair. i love the vfds on this era of HP gear.

[Dimlowuk]

So, did the cleaning fix the trigger problem?

[gerrysweeney]

Not really, its the same. Having played with it more its just less sensitive than the Racal-Dana counter. Once you have 3V or more of drive the HP works and triggers OK, its a lot happier with square waves than it is with sine waves too. Once I have done the power switch mot I will do a side-by-side comparison video to show the differences.

[gerrysweeney]

Hi Malcolm, thanks for your comment. That is certainly possible but it definitely emanated from outside the unit, perhaps something sitting on top of it. Thanks for watching. Gerry

[gerrysweeney]

Yeah, these are old counters so I guess the rubber is breaking down with age and getting back to their liquid state :(

[paulstadler]

I just took apart an old 53132A that had the same mess on the bottom of the circuit board.  It must have been a rubber foot attached to the bottom of the board that completely dissolved.  It was a horrible mess. IPA and a brush got most of it off, but some of it is still soaked under caps and resisters on the bottom of the board.  The 53132A appears to have the same circuit board as the 53131A except the 2nd FPGA is populated.

[LeeWalklin]

Hi Gerry.
I’m in the market for a decent frequency counter, either a hp 53131a or a racal 1998!!! What do you reckon please? And obviously things to look out for with these counters.
Like the vids by the way, very informative.
Cheers 👍