HP5245L Freq. Counter Repair - Page 1
Forum section: electronics / repair

author: gmilliorn
author_rank: Contributor
timestamp: August 21, 2014, 04:13:41 am
content: I'm trying to repair an old HP5245L (Nixie) freq. counter. The counterpart works fine, the oscillator does not. The A26 card provides thereference clock at pin 1-5, it is 0V.Here's the schematic:IMG is not working for me - here's a link:The voltages are all pretty close to what HP noted:C B EQ1 -13.4 -8.0 -7.2Q2 -10.6 -3.3 -2.6Q3 -10.5 -2.6 -1.9Q4 -6.5 -2.3 -1.4Q1 was furthest off, and since the AGC feedback is AC coupled I keepthinking it must be around Q1. I replaced it with a 2n2907 which seemspretty close (detailed specs on the 1853-0009 transistor seem sparseotherthan PNP + 30V). Nofix, though.I removed the (A26) card and powered it with a bench supply anda 1MHz xtal across J2-1 to J2-4, with no change, so I'm prettysure it is localized to this card.L1 is not open and pulled C6 and it measured .064 uF. I have to pullthe parts to check them so I haven't done everything.If anyone has ideas what to check I'd sure appreciate it!Gary

author: mij59
author_rank: Frequent Contributor
timestamp: August 22, 2014, 05:23:32 pm
content: Hi,How did you measure the output pin 1-5 ?

author: gmilliorn
author_rank: Contributor
timestamp: August 22, 2014, 11:16:12 pm
content: With a scope and 10X probe. Do you think I'm affecting it, somehow?The HP manual shows waveforms, but unfortunately not for the oscillatorside of the card. The pin 1-5 output of the card should be about the sameas the external input option, which is 2V pk-pk max.I'm not even sure of the oscillator type; the L-C arrangement doesn'tresemble what I can find online, though I guess Colpitts is most similar.-Gary

author: mij59
author_rank: Frequent Contributor
timestamp: August 23, 2014, 03:53:56 am
content: Quote from: gmilliorn on August 22, 2014, 11:16:12 pmI don't think probing the output would cause the oscillator to stop.If you connect a xtal you also need connect the capacitors as shown in the schematic.Check the connections between the A26 and A24 board.Check board A24 for bad solder joints.Trimmers can lose capacitance due to oxidation, check C1, C2, C3.

author: gmilliorn
author_rank: Contributor
timestamp: August 23, 2014, 05:28:37 am
content: "Trimmers can lose capacitance due to oxidation, check C1, C2, C3"I didn't know that, thanks - I'll look into that. C2/C3 are accessible, C1is inside the oven which I was hoping I don't have to open that up.Building up a proper set of caps on the crystal is a good idea, thanks, Ishouldn't have tried to skip that (thought I would at least see a burst).(And 0.017uF ? Odd, I don't think I've ever seen that value before).-Gary

author: Rasz
author_rank: Super Contributor
timestamp: August 23, 2014, 01:12:42 pm
content: Quote from: gmilliorn on August 21, 2014, 04:13:41 amjust upload it here as an attachmentimgur will delete this picture in few months and we will end up with a post with dead link.

author: gmilliorn
author_rank: Contributor
timestamp: August 23, 2014, 04:01:09 pm
content: Thanks, here's that image using attach.I tried hooking up the multiple capacitors on the crystal I'm connecting, it stilldoesn't work.Interestingly, when I short from the AGC node (CR1-CR2 common) to the baseof Q2, I get an oscillation: about 57kHz 2V pk-pk. That seems to suggest theQ2-Q3-Q4 path is at least OK, and that it is Q1 or thereabouts.I suppose it is possible the 2N2907 is not a good substitute for the HP 1853-0009.Sphere has them for $7 ea. which I was trying to avoid.

author: mij59
author_rank: Frequent Contributor
timestamp: August 24, 2014, 05:33:22 am
content: Quote from: gmilliorn on August 23, 2014, 04:01:09 pmDid you check the reaming capacitors round Q1, CR1 and CR2?Maybe you could use transistors like BFxxx

author: gmilliorn
author_rank: Contributor
timestamp: August 28, 2014, 02:05:10 am
content: I guess at this point I need to start pulling off all the parts and checking them oneby one.I have an old capacitance meter, it can't measure them in-circuit (if that's even possible).It might also be the 2n2907's, the only cross references to HP 1853-0009 I couldfind are:1853-0009 = TI SM5727TI SM9477Mot SS2111Fairchild S15097But all those part numbers are odd, probably either custom for HP or the gov.

author: mij59
author_rank: Frequent Contributor
timestamp: August 28, 2014, 04:53:16 am
content: Quote from: gmilliorn on August 28, 2014, 02:05:10 amIn-circuit testing can be tricky, in this case, remove the components to test them.I found a cross reference list , sadly the 1853 0009 is not on it, but the 1853 0008 and 1853 0007 are.It's a bit of a gamble, maybe the 2N3251 is a replacement for the 1853 0009.

author: gmilliorn
author_rank: Contributor
timestamp: August 29, 2014, 02:18:31 am
content: I've started pulling caps and checking them; a few are slightly off. Perhaps I should justreplace all the discretes as that is cheap. The inductors are not open, and I don't have anLCR meter or a sine wave oscillator so I can't think of a way to check those out.That leaves Q1 yet again: since it seems like Q2-Q4 are working, I might move Q3 to Q1 andput the 2N2907 there.To try another transistor, I assume the parameter that is next most important (after 30Vrange) is high gain. I really wish HP had shown a few waveforms on the left side.

author: mij59
author_rank: Frequent Contributor
timestamp: August 29, 2014, 03:48:57 am
content: Quote from: gmilliorn on August 29, 2014, 02:18:31 amIf the components test good there's no need to replace them.The output level of Q1 could be small, at what sensitivity setting of the oscilloscope did you test Q1 ?

author: gmilliorn
author_rank: Contributor
timestamp: August 31, 2014, 06:52:38 pm
content: Removed at least one lead and measured a lot of parts, and made the followingchanges:* Swapped Q1 and Q2* Replaced R8 (was 4600)* Swapped C6 for C3, C6 was 0.056uF and I had no spares.Now I have some progress: 1MHz 1V pk-pk.This is with a bench supply but attached to the HP5245's crystal circuit. Not all isgood, though:* It takes about 16s to start up warm, about 2X cold. First it is just DC then someimpulse noise and finally a sine wave ramp up in voltage.* When I re-install the card in the chassis, it stops working. The supply fromthe '5245 is spot on at -15V, so it's something else.This seems to confirm that Q1 was bad and that the 2N2907 is not a goodsubstitute. I'm going to look for a higher-gain 30V PNP, otherwise I mighthave to but a few real ones at $7 ea.The only oscillator connections to the backplane are power/ground and oscoutput, so either the output connection is shorted, or being placed in a shieldedenvironment keeps it from starting up.

author: gmilliorn
author_rank: Contributor
timestamp: September 13, 2014, 12:57:20 am
content: Still could not get it working while installed in the system, so I guessed that maybe the alligatorclip I used to bridge the two independent grounds (J1-1 and J1-3 are separate grounds for theoscillator and feedback portions) was adding inductance.So I soldered a direct bridge between the two and sure enough, it no longer worked.So, I removed the bridge and ... now it no longer works. At all. Argh.I'm about to the point where IA. remove and replaceeverything, orB. remove and install a more modern oscillator. Something likeany of these:http://cds.linear.com/docs/en/application-note/an12fa.pdfas the oven control circuitry is still working (measures correctly, at least)that would seem to be the hard part.

author: mij59
author_rank: Frequent Contributor
timestamp: September 13, 2014, 03:54:53 am
content: Quote from: gmilliorn on September 13, 2014, 12:57:20 amIt would be wiser to replace Q1 and go from there.If you want to replace the oscillator use a ocxo.An other optionC. buy an other counter.

author: gmilliorn
author_rank: Contributor
timestamp: September 13, 2014, 03:53:28 pm
content: Oh, I could buy another counter but this was supposed to be "fun". I've workedwith nixie's before (clocks, etc). so I assumed it was cheap on ebay because ofproblems in the display section. I can supply a external 1MHz source at the backand it works, so it is all in the oscillator section.I even created an LTspice model of the circuit in an attempt to understand how itworks, so if nothing else, I learned that oscillators rely on thermal noise to startup so spice simulations of oscillators are difficult-to-impossible.I think replacing Q1 is indeed the next step, thanks.

author: gmilliorn
author_rank: Contributor
timestamp: September 27, 2014, 03:38:43 pm
content: Well, I broke down and ordered the 1853-0009 transistors from sphere.ca.I guess I'll see if there is anything magic about them.In for a penny, in for a pound...

author: gmilliorn
author_rank: Contributor
timestamp: September 04, 2015, 04:12:39 am
content: After trying to drive the crystal oven externally, and failing, it seemed as though itmust be the crystal that had failed. Not really a component I thought was going tobe the issue. Replacement ovens are really expensive.Fortunately, the OXCO is capacitively coupled to the drive card, so all I hadto do was inject a reference clock. I had a Millirem OXCO, but 5 MHz, soafter powering and dividing it, it works great.It might even be better, though I have one nagging doubt: does the dividerintroduce any uncertainty? It's all about the switching thresholds in the end. Ahwell, either way it is better than what I had before (nothing).

author: mij59
author_rank: Frequent Contributor
timestamp: September 04, 2015, 05:49:35 am
content: Thanks for the updateThe level conversion from the 5 MHz sine wave to square wave for the input of the divider is the only critical part, would you post the schematic ?To get similar specs as the original ocxo you need something like the MTI 260 5MHz.

author: gmilliorn
author_rank: Contributor
timestamp: September 09, 2015, 01:48:24 am
content: You're right about the accuracy, I though the '5245 was 1 part in 10^8 but it's 1 part in 10^9, much better.I can't seem to find my schematics, so I scribbled this in paint.net:I used the schmitt to try to avoid having the sine wave slowly transition across the TTL switching threshold.

author: flanneltuba
author_rank: Contributor
timestamp: February 05, 2022, 07:23:27 pm
content: For the sake of future travelers who find themselves looking to cross list the HP transistor 1853-0009, I happen to have an HP 5232A Counter which uses these parts on its A9 1MHz crystal oscillator board. On my particular A9 card rather than the parts being marked with the elusive 1853-0009 HP part number, these transistors are marked RCA 2N384.The parts appear to be original from the factory, with no signs of having been replaced -- the solder is unblemished in any way that might indicate having ever been reworked.I have also designed a modern replacement Nixie decoder+driver board for the aging custom HP neon optical decoder boards, found in this generation of HP counters. Let me know if you're interested, I can post my design here. I'll post a pic for show and tell anyway.

author: factory
author_rank: Super Contributor
timestamp: February 05, 2022, 10:41:45 pm
content: HP also used the 4514 (1820-1683) decoder IC for the display boards in the early 80's. They used individual transistors instead of those ULN2003 arrays. Details are in the really crap quality manual scanned by Agilent some years ago.David

author: flanneltuba
author_rank: Contributor
timestamp: February 06, 2022, 04:43:06 pm
content: Indeed, I got a conceptual nudge from a photo of one of the later variations of the display card I spotted on ebay. The photo was too grainy to see the actual p/n of the 24 pin dip IC they'd employed, but from the look of the rest of the BCD counter logic on the card, it looked like the decoder and driver where clearly a retro fit onto the original counting circuit. I begged Google for a schematic or reference to the newer displays, but came up empty and set forth to just design something myself. So, ruling out the idea that they used any custom rolled ICs here, I concluded they must be using some kind of standard decoder/demux. From there it was a short leap to start playing with the 4514. So, perhaps to say I designed the circuit rings a little phony, but reverse-guessing the rest of the circuit without a schematic and only the grainy pic to go off of, at least qualifies me for honorable mention at the next gathering of the Technology Plagiarists Anonymous meeting. In any case, I now have a full set of clearly lit and responsive nixie displays, as opposed to the drunkenly foggy mess they were prior. Success.- Scott

author: Paul B
author_rank: Contributor
timestamp: February 06, 2022, 09:41:05 pm
content: hi I would love to get the CCT diagram for the replacement to the neon and photo resistiv display driverps there is a fix that i have used on a number of these displays when thy will not tiger / count properlyPaul

author: factory
author_rank: Super Contributor
timestamp: February 06, 2022, 09:51:49 pm
content: Quote from: flanneltuba on February 06, 2022, 04:43:06 pmDiagrams for the later display boards & mods for the 10544A type crystal oven, are in the manual on the Keysight webpage. Would be nice to find an original of the late manaul, as the scan quality is complete & utter shite.https://www.keysight.com/gb/en/assets/9018-02735/user-manuals/9018-02735.pdfI took the other option with mine & bought some spare boards from Sphere to rob the decoder plates & neon assemblies to repair mine, had two with corroded traces on the decoder plate.Note: with these that there are at least two different decoder plates, for the various BCD output code options.P.S. It's a good idea to add a separate fuse for the small transformer for the crystal oven, that way if the oven heater shorts out, it hopefully won't burn the transformer up.David

author: Paul B
author_rank: Contributor
timestamp: February 06, 2022, 10:03:15 pm
content: hi from memory over 35 years there is the high frequency and low frequency in the same counteras the count repels through and only the lower digits are the high frequency counterswhen you switch to store on the back and the frequency is not the same for a fixed frequencythe problem is usual the neon ageing and the trigger voltage has changed so the flip flop is not in correct statei can enplane how to sort this if required Paul B

author: Paul B
author_rank: Contributor
timestamp: February 06, 2022, 10:17:34 pm
content: If you want a better scan of a manual ARTEK do them for about $10

author: factory
author_rank: Super Contributor
timestamp: February 06, 2022, 10:26:26 pm
content: Artek don't have the later manual, or the 1980 change sheets, I have dead tree editions of the two that Artek offer.Some pictures of the failed decoder plate I had, the traces had corroded away & cleaning made the damage more obvious, a replacement from a donor board cured it. There are at least two types for the +1224 , +1248, -1248 BCD output options.Different version.David

author: flanneltuba
author_rank: Contributor
timestamp: February 07, 2022, 04:36:09 am
content: @Paul B: I tried a number of ways to improve the degraded performance of the original photo coupler devices myself, to no avail. They suffer from pure age related deterioration, is my guess. All things must pass...Here for better or for worse, is a pic of my the diagram of my CD4514 + UNL2003 replacement concoction, which works quite well. It is effectively a take-off of the HP upgrade, but with fewer components."Please excuse the crudity of the model. I didn't have time to build it to scale or paint it."I can redraw this into a more conventional schematic drawing if needed, this is just my crude working sketch from my bread-board development work.But...it works. Refer to the previously posted pics for where to tie in the ABCD counter bits, -150V, GND, and X-fer In to the original circuit. Let me know if you have questions. Happy to help.- Scott[Edit: Also, you will need to replace the common anode resistor for thenixiedisplay with a 12KΩ resistor, and disconnect the R6, R7, R8, and R9 resistors to the neon bulbs. My pic above shows CR1-8 disconnected, but you can leave them in; they do no harm to stay.]

author: Paul B
author_rank: Contributor
timestamp: February 07, 2022, 02:30:53 pm
content: Hi ScottThank you for the picture regarding the photo resist yes a lot of counters might fail with that ageing bit neon ageing can be sortedI have recently given a few of these counters to a friend so will probably get involved in getting them goingI think it would be worth making a slightly better drawing as a lot would like to see it passably on the HP sitePaul

author: flanneltuba
author_rank: Contributor
timestamp: February 07, 2022, 06:23:04 pm
content: Not having any proper schematic drawing software I did a quick search and opened the first free schematic software that looked reasonably uncomplicated, that being Scheme-it offered on the DigiKey site. I spent an hour or so and got a ½ way readable drawing sketched out. I took a quick screen shot of it, since the software seemed reluctant to allow me to actually save my final product, so it's surely doomed to disappear as soon as I close the browser page it's on.So, well, for better or for worse, and surely a trained practitioner of such software could do far, far better, here's a screen capture of my HP nixie display driver replacement circuit. As far as I can tell this is essentially the same design as HP's later display drivers, but with ULN2003 darlington arrays instead of discrete transistors. If someone has an actual schematic of the HP circuit, I'd be interested how close I came to duplicating it from a grainy ebay snapshot of one of these later display cards.- Scott

author: factory
author_rank: Super Contributor
timestamp: February 07, 2022, 09:28:06 pm
content: Here are a couple of the crappy scanned pages from the manual on the Keysight webpage, there are several more diagrams for different variants, all are in the change sheets at the end of the pdf.https://www.keysight.com/gb/en/assets/9018-02735/user-manuals/9018-02735.pdfDavid

author: Dave111
author_rank: Newbie
timestamp: September 18, 2025, 06:55:14 pm
content: Glad I found this page. I've got a 5245L; counter works great - all except the 'internal' oscillator. Hooking up an external 1 Mhz oscillator (actually using a HP 101A which works great) proved all else works OK. I tried troubleshooting and found similar road blocks like no cross reference for the 1853-0009 transistor, etc. Not sure why I didn't try swapping some transistors first, but I went for the crystal oven thinking perhaps the crystal might be bad. I found the original HP Crystal had a slight crack in the glass envelope and after just handling it a few times very carefully, the glass envelope separated in half. I'm not sure if such a crystal would work or not.?.? I went on the search for a replacement and unable to find the OEM crystal. I did find another 1 Mhz glass enveloped crystal that doesn't seem as 'robust' as the OEM HP one and re-assembling now. I would really like to hear the latest news if any new items were found and/or fixed to get the internal oscillator working.

author: factory
author_rank: Super Contributor
timestamp: September 18, 2025, 08:37:09 pm
content: As your flag is the USA, you should be able to find a replacement oscillator assembly, HP didn't offer the crystal separately as far as I know.Some info attached for the 1853-0009 PNP silicon transistor, from the fiche CuriousMarc scanned.And the parts list of the A24 crystal oven assembly, crystal "A24Y1" not separately replaceable (NSR), with error next to it, someone copy pasted (before that was a thing) from display boards part list "part of readout block".David

author: gmilliorn
author_rank: Contributor
timestamp: September 19, 2025, 12:47:50 am
content: For my 5245, the oscillator would work externally (external xtal) but not with the canister, so it may have had thesame fate as yours. As I didn't think I'd have much luck tearing it open, fixing it making it whole, so I replacedit with an OXCO which worked well. Given what I paid for the transistors vs. OXCO prices, it's not an unattractiveoption.