Frequency counter won't count. - Page 1
Forum section: electronics / repair

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 02:32:56 am
content: I bought a HP 5340A and when i first got it counted and accurately. Then i put it on the shelf, not one thing changed and all it will show are zeros, and when i change ranges either MHz or GHz and the decimal point also changes. Could someone please help me before i rip my hair out?

author: Ampera
author_rank: Super Contributor
timestamp: July 06, 2017, 02:54:00 am
content: Bolt an HP calculator to it. It will start counting perfectlyThe calculator, not the machine.

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 03:06:39 am
content: Quote from: TwoOfFive on July 06, 2017, 02:54:00 amGood laugh but ultimately not a solution to the existing problem of the expensive paper weight that used to count frequency then stopped.

author: Ampera
author_rank: Super Contributor
timestamp: July 06, 2017, 03:20:32 am
content: You say it's expensive? Attempt percussive maintenance, that always helps matters.Sorry for joking around, I wouldn't know what the issue would be.

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 03:31:22 am
content: Quote from: TwoOfFive on July 06, 2017, 03:20:32 amThe jokes are fine, they make me laugh and consequently help keep me from doing "advanced percussive maintenance" to the thing

author: Vgkid
author_rank: Super Contributor
timestamp: July 06, 2017, 05:40:52 am
content: Here's the manual:https://elektrotanya.com/hp_5340a.pdf/download.htmlSince it previously worked, make sure everything is seated. Grab a dmm, and check the power rails. If it is like other HP counters that use a socketed relay for power, a bad connection will cause some strange results.

author: TheSteve
author_rank: Unknown
timestamp: July 06, 2017, 06:14:05 am
content: Which input are you using, what is the input selector set to and what voltage/frequency signal are you feeding into it?

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 06:35:14 am
content: Quote from: TheSteve on July 06, 2017, 06:14:05 am50 ohm bnc i tried front and back. Voltage should be very low level, a hair above min level on my GFG-8020H. Frequency between 10 Hz and 55 MHz. It is through a scope probe but the same probe worked before i moved it.

author: TheSteve
author_rank: Unknown
timestamp: July 06, 2017, 06:55:39 am
content: Is it a 10:1 probe? Anyway, you'll need to use the front BNC input for lower frequency use. Keep the range switch fully left.

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 07:33:31 am
content: 10x/1x probe and yes i did have it on 1x and i tried every range.

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 07:37:52 am
content: No matter what i do it locks at 00.000000 MHZ on 1 hz range, it used to go into a KHz range and measure

author: Gyro
author_rank: Super Contributor
timestamp: July 06, 2017, 11:51:12 am
content: I'd check that its crystal oscillator is still working, especially if it's an ovened one. It might have suffered a thermal cycling related failure.

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 12:43:07 pm
content: Quote from: Gyro on July 06, 2017, 11:51:12 amWhen i tested it it read 7-8 MHz and climbing on my working frequency counter, i writ it off to the scope probe but could that be it?

author: rdl
author_rank: Super Contributor
timestamp: July 06, 2017, 12:53:50 pm
content: Be sure to try with a different connector. Even 2 conductors of straight wire will be okay for testing. I bought a new oscilloscope once that came with 1 probe open, so never trust anything.

author: neo
author_rank: Super Contributor
timestamp: July 06, 2017, 07:56:29 pm
content: Quote from: rdl on July 06, 2017, 12:53:50 pmI know both probes work as i have tested both. With either probe the frequency jumps between 7.5 and 8.5 MHz before semi stabilizing at 8 MHz and some change. I'm going to assume that is bad? It also only outputs when the unit is turned on.

author: Vgkid
author_rank: Super Contributor
timestamp: July 06, 2017, 11:56:04 pm
content: That doesn't sound good at all. 7-8MHZ, even measured with a scope. Is very very far from the correct frequency.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 12:08:00 am
content: It could be that the capacitance of the scope probe messes up the oscillation. Especially if set to 1x. Set it to 10x and try to find a buffered node to measure the frequency at (for example an external 10 MHz output).

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 12:22:48 am
content: Quote from: alm on July 07, 2017, 12:08:00 amActually that is what i last tried, the 10 MHz out with 10x on the probe.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 12:34:55 am
content: I must have missed that when reading your posts. If the 10 MHz output is outputting ~8 MHz, then there is definitely something wrong around the oscillator. The obvious place to start is measuring power supply voltages and ripple. The service manual should be helpful for this.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 05:31:41 am
content: -15V could not find board.+15V OK-5V RF OK-5V DG OK+5V RF OK+5V DG FAIL 4.67 MAXIMUM+11 TB OKWhile probing that last one it started counting again, i left it in self check and was watching for anomalies, so this give you any clues? I'm thinking maybe a loose card? It also started doing the 10 MHz out it should have been doing.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 05:42:50 am
content: I put the cover on and it broke again. By broke i mean not displaying and/or counting properly.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 05:57:19 am
content: Also when it does work properly all i get is 3 digits.

author: Vgkid
author_rank: Super Contributor
timestamp: July 07, 2017, 06:11:51 am
content: Check to make sure everything is seated, then recheck your power supply. Do you have the 175v rail?

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 06:17:47 am
content: Quote from: Vgkid on July 07, 2017, 06:11:51 amI took out and put all power cards back in and as for the 175V rail it has to work as the display is fully functional. Every digit lights except when counting where it will only display 3 digits.

author: VK5RC
author_rank: Unknown
timestamp: July 07, 2017, 08:37:13 am
content: Does it have a freq standard input switch? I had an old HP counter that the switch was intermittent, the internal reference goes through it as well.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 08:43:25 am
content: It has a switch to switch between internal and external 10 MHZ reference frequency.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 08:58:08 am
content: To summarize so far.All voltages check, except 5V DG it is .7 low with no room to adjust.It is outputting very near 8 MHz when on , when working it is 10 MHz.Switch appears to work from a basic sense that it affects the 10 MHz outIf board 60019 is touched or moved i get ghost digits in recurring locations. To be fair i can understand this one.Gate light may be erratic.I know i may be a bit slow but this is the first thing i have ever tried to fix.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 01:15:40 pm
content: Probably excessive current draw pulling +5 V DG down. Check for shorted tantalum caps or parts on that rail that get excessively hot.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 07:07:33 pm
content: A19-A24 removed, voltage raised to 5.05A-22 reinserted, voltage drops to 4.95A-23 reinserted, voltage drops to 4.82A-21 reinserted, voltage drops to 4.66A-20 reinserted, voltage drops to 4.51A-19 reinserted, voltage drops to 4.42A-24 reinserted, voltage drops to 4.39Seems like a dodgy +5V DG regulator to me.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 07:17:09 pm
content: So with all 6 boards it is up to 5.5 V? So either all the boards draw excessive current, or there is something wrong with the power supply. What about the ripple?Did you complete the power supply troubleshooting as discussed in section 5-39 (page 5-20) of the service manual? What was the unloaded voltage? What was the voltage with the resistive load?

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 07:57:22 pm
content: Quote from: alm on July 07, 2017, 07:17:09 pmNot to 5.5, 5.05 and i could not find A-30

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 09:02:21 pm
content: I removed all cards again and connect a 20 ohm resistor between +5V DG and ground, was 5.20 unloaded withthe load it dropped to 4.90+5V RF by comparison only dropped .03 volts when loaded.The load for +5V DG is supposed to have a 7.5 ohm load so if it drops .3 volts at only 20 ohms something is wrong, what should i check? With a 10 ohm load it drops to 4.7V

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 09:07:45 pm
content: Yes, it sounds to me like there is a problem with the +5 VD power supply. What was the ripple like both unloaded and with the resistors?

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 09:39:19 pm
content: I apologize for image quality it is quite hard to photograph an analog scope though i believed these might be of more use than a description. They are labeled for the condition and this is with the probe on 1x, the position is off because i had to adjust it quite alot to get the waveform on screen.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 09:54:26 pm
content: Is that DC coupled? What is the vertical scale? Is it the same for each picture? It looks like the regulator is dropping out due to insufficient decoupling. I would expect the electrolytic filter capacitor before the pass transistor to measure very low capacitance. Replacing it should fix the +5 VD rail.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 10:07:14 pm
content: Quote from: alm on July 07, 2017, 09:54:26 pmThe scope is set to dc, the scale is 5V with 1x probe. Same across all pictures. 0V position was way down off the bottom of the screen to get that in shot.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 10:17:31 pm
content: So I am guessing 1 V/div. Then that ripple is way too much. As I mentioned, try checking the filter cap for that rail. If you do not have a way to measure it (e.g. LCR meter), try soldering a capacitor with a similar value and the same voltage rating in parallel to the suspect cap. Watch the polarity. If that reduces the ripple to negligible levels (as it should be), then replacing the cap should fix it. If not, then move on to other parts like the rectifier.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 10:38:09 pm
content: Quote from: alm on July 07, 2017, 10:17:31 pmI don't have an lcr meter (yet) and i don't have have a clue which capacitor is for the 5V rail, reading manual though not finding much information about the capacitors.

author: neo
author_rank: Super Contributor
timestamp: July 07, 2017, 11:52:09 pm
content: In absence of an lcr meter i have devised a test, i connect a known resistor and know voltage to the capacitor time how long it takes to reach 1 volt and then check the math. For example a 15V 4000uf capacitor connected to 10v through 10.12k ohm resistor should take 5 seconds to reach a volt. If it passes that i also check resistance across capacitor and if infinite it passes.

author: alm
author_rank: Super Contributor
timestamp: July 08, 2017, 12:00:44 am
content: That approach works fine. You will get a reading that is too low for capacitors with a high equivalent series resistance (ESR), but replacing those is not exactly terrible.In this case it may be easier to just add a parallel cap and see if the ripple improves, though. Measure ACV with your DMM on the +5 VD rail. Put a cap in parallel to the suspect cap (watch voltage rating and polarity). If the ripple improves, then that cap is likely the culprit (unless it is one of the smaller ones after the pass transistor). It is likely one of the big filter caps with a moderate voltage rating close to the secondary outputs of the transformer.

author: Vgkid
author_rank: Super Contributor
timestamp: July 08, 2017, 12:08:53 am
content: That is definetly a lot of ripple. If you have an appropriately voltaged cap (even if it is lower in capacitance) substitute it in if your rails go to normal, then you know what caps are bad.Easiest: buy the caps that are listed in the manual, replace every cap in the psu. It will be painless that way.

author: rdl
author_rank: Super Contributor
timestamp: July 08, 2017, 12:30:20 am
content: If you can't identify the actual filter cap, just connect a known good one of some reasonable size from the regulator input to ground (watch polarity) and look for an improvement in the ripple.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 12:44:35 am
content: There are a couple of reasons why i can't just change the capacitor or put a capacitor between regulator input and ground. The first is the manual does not say which capacitor is which as far as i can tell, and it is a dual regulator board so im not entirely sure which is which, there is a different regulator for RF and DG.

author: rdl
author_rank: Super Contributor
timestamp: July 08, 2017, 01:10:32 am
content: Quote from: neo on July 08, 2017, 12:44:35 amYou don't need to know what or where the existing filter cap(s) are. You're just trying to figure out what the problem is at this point, not to fix it. Since there are multiple regulators, try adding a capacitor to each one separately, one at a time, and look for an improvement. Adding temporarily more capacitance will not cause a problem (it's generally not something you can have too much of). You may only need another 500 uF - 1000 uF to see a difference. Just make sure to get the polarity right and use a capacitor with high enough voltage rating.

author: TheSteve
author_rank: Unknown
timestamp: July 08, 2017, 01:12:06 am
content: You should change the 6 main filter caps before checking anything else.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 01:32:00 am
content: I have tested all of the filter capacitors and they are fine. The reason i don't want to change them is for two reasons.I don't have any new capacitors so anything i got is as bad if not worse than these and my secondary reason is that they are custom fitted to the PCB, i could change them but it wouldn't look quite right.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 02:43:58 am
content: Now the decimal point won't move at all, before the capacitor checking it did.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 02:49:43 am
content: The oscillator is oscillating at EXACTLY 10MHz give or take nothing. 10.00046 MHz.

author: alm
author_rank: Super Contributor
timestamp: July 08, 2017, 02:49:52 am
content: Could very well be a bad connection if you unplugged all boards. Possibly a dry solder joint on one of the connectors. Although if that ripple is still present, then that could also be responsible for the digital circuits not working reliably.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 03:07:39 am
content: Quote from: alm on July 08, 2017, 02:49:52 amThe ripple is still present. Also the display board is rather loose, if vibrated much i get ghost digits. By vibrate i mean tap, consequently i can also tap A-24 to get rid of ghost digits. I got the decimal to work again, a board was loose.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 03:45:08 am
content: I cannot make much sense of the schematic for the +5V regulator board, it took me a long time to even find the schematic.

author: Cubdriver
author_rank: Unknown
timestamp: July 08, 2017, 04:45:43 am
content: That seems like an awful lot of ripple on a 5V logic power supply line. A suggestion for seeing just the ripple - AC couple the scope input. That will get rid of the DC level and let you see only the ripple, and make it easier to measure.I'm going to try to excavate my manual and get mine onto the bench. Perhaps I'll be able to help hunt things down with you.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 04:58:25 am
content: Quote from: rdl on July 08, 2017, 12:30:20 amDidn't work, i also tried putting a capacitor on the output and that reduced the ripple slightly. I used a 3500uf cap.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 05:09:30 am
content: I put a capacitor on 5V DG output and it worked, it started counting again. The scope probe is set to 1x and AC , the center line on screen is center line of voltage present.1st shot, 10v scale.2nd shot, 2v scale.

author: Cubdriver
author_rank: Unknown
timestamp: July 08, 2017, 05:14:17 am
content: Sounds like a bum cap on the digital power supply, then.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 05:31:18 am
content: This is it on 20 mv range with 50,000 uf capacitance, am i the only that thinks this problem can be solved with a super capacitor?

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 05:43:35 am
content: Now that the power supply is at least under control it will only show 3 digits when counting, i have it on self check and in resolution scale of;1 it reads .001 KHz;10 it reads 0.00 KHz;100 it reads 00.0 KHz;1k it reads .000 MHz;10k it reads 0.01 MHz;100k it reads 10.0 MHz;1m it reads .010 GHz:The left 4 will flash 0 when i change ranges but that is it, otherwise they are off.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 06:02:44 am
content: After being mildly agreeable for a couple of minutes it did this. 1x probe ac coupled and on .2V range. Still allows it to count though.

author: Cubdriver
author_rank: Unknown
timestamp: July 08, 2017, 06:17:34 am
content: I had a long reply typed up and the effing webpage just gorked and ate it.I'm looking at the +/-5V digital supply schematic (fig. 8-34) on page 8-75 of the manual I have here. The +/- 5V digital supplies are fed from a bridge rectifier (CR1) that, combined with the center tapped transformer secondary it's fed from is configured as a pair (positive and negative) of full wave center tapped rectifiers. The resulting positive and negative rails are filtered by A30C5 (+) and A30C6 (-). Based on the A30 board drawing on pg 8-73, it looks like A30C5 & 6 are the two rearmost of the '6 pack' of filter caps there adjacent to the regulator boards. The left rear one is A30C5, and the right rear one is A30C6. They are 4000uF, 15V (page 6-27 in the parts list).Hope this helps a bit.-Pat

author: Cubdriver
author_rank: Unknown
timestamp: July 08, 2017, 06:18:57 am
content: Quote from: neo on July 08, 2017, 06:02:44 amI'm curious - where are you connecting the probe to pick this up? TP2 on the A32 board?-Pat

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 06:27:26 am
content: Quote from: Cubdriver on July 08, 2017, 06:18:57 amYes i am. Why?

author: Cubdriver
author_rank: Unknown
timestamp: July 08, 2017, 06:30:06 am
content: Quote from: neo on July 08, 2017, 06:27:26 amJust wanted to be sure I knew the source. What is the frequency of the ripple - how much time for each cycle?

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 06:40:12 am
content: 120 Hz, the last shot was actually 10x sorry for the confusion.

author: Cubdriver
author_rank: Unknown
timestamp: July 08, 2017, 06:54:49 am
content: Quote from: neo on July 08, 2017, 06:40:12 amDarn!! I was hoping you'd say 60, which could have meant one of the rectifiers was failing. So much for that brilliant idea!Are you putting your additional filter capacitance across the actual filter cap, or directly on the regulated output? If directly on the output, it could be confusing the regulator by messing up the response time of the control loop. If you have it across A30C5, then never mind; if not and it is on or near the output and beyond the regulator pass transistor, try to get it onto C5 instead where the circuit expects to have filtration. That might help things out.And on that note, I really need to crawl off to bed - it's 0300 here in these parts. Good luck, and I'll try to offer more suggestions tomorrow if it's still acting up.-Pat

author: TheSteve
author_rank: Unknown
timestamp: July 08, 2017, 06:59:50 am
content: I have two 5340A's. Both of the Nixie tube vintage. I still say replace all 6 of those caps. The original's are snap caps which are very expensive to replace but you can get cheaper replacements that fit just fine with a little soldering. I liked that the originals bolted in but the cost(and smell) of the originals made up my mind for me.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 07:12:16 am
content: Quote from: TheSteve on July 08, 2017, 06:59:50 amI quite like the way those caps mount to it as well and i am not discounting your advice to replace them it is just that i would have to buy them as i don't have any.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 07:25:46 am
content: I dare say that is approaching reasonable, 55,000 uf in parallel with C5 1x probe (i checked to make sure) 20mv scale.

author: rdl
author_rank: Super Contributor
timestamp: July 08, 2017, 08:05:34 am
content: 55,000 uF ? !!! With that much filter capacitance you probably don't even need a regulator.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 08:08:00 am
content: As little as 4000uf makes a difference so i guess i will have to replace the capshttp://www.ebay.com/itm/112056031209?var=41099432659615000 uf version of these for C5 and C6 work?

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 08:10:03 am
content: Quote from: rdl on July 08, 2017, 08:05:34 amThat was as a test i reduced it to 4000 uf, just like spec, and it remained happy

author: TheSteve
author_rank: Unknown
timestamp: July 08, 2017, 08:14:16 am
content: I used Digikey part # 338-1626-ND

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 08:16:13 am
content: Quote from: TheSteve on July 08, 2017, 08:14:16 amDoes it fit the same as the originals?

author: TheSteve
author_rank: Unknown
timestamp: July 08, 2017, 08:20:07 am
content: They nicely fit in place of the originals, but do have to be soldered.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 08, 2017, 08:21:30 am
content: Quote from: Cubdriver on July 08, 2017, 06:54:49 amA bridge rectified 60Hz is 120Hz.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 08:22:23 am
content: Quote from: TheSteve on July 08, 2017, 08:20:07 amI will have to bodge something in temporally though those will work nicely. Any thoughts about the display only giving me 3 digit resolution?

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 08:37:00 am
content: I put in a Sprague electrolytic i had laying around, its not much newer 80s vintage but it does work. The frequency counter is very happy, only problem is it is so tall i can't put the lid on though i do plan to replace it with the ones Steve mentioned in a month or two.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 10:11:25 am
content: Near as i can tell it now works, thanks to all who helped me. Two big questions remain i get a ghost digit 4 in the far left tube though tapping A-24 solves it, anyone got any ideas? The display assembly is meant to be fastened down but the screws are missing.Secondly, In check and 10Hz-250MHz i get only 3 digits is that normal?

author: Vgkid
author_rank: Super Contributor
timestamp: July 08, 2017, 08:36:15 pm
content: Does the manual I linked, tell what to expect from the self check?

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 08:47:25 pm
content: OK so the 3 digits are not normal. Anyone got any ideas?

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 09:51:13 pm
content: If i hold reset or put it in the18 ghz mode it will show all digits, displaying 0 due to lack of input.

author: neo
author_rank: Super Contributor
timestamp: July 08, 2017, 10:58:47 pm
content: EDIT;I have a very odd and erratic glitch i connect my Simpson 415A signal generator to the 5340A and it will erratically count 100KHz as 200KHz. Connect the 5340A to my GFG-8020 function generator and it counts properly. The Simpson 415A, when connected to my other frequency counter, oscillates correctly.

author: VK5RC
author_rank: Unknown
timestamp: July 09, 2017, 01:19:27 am
content: Sounds as though you are getting there.IF it is of any help re the old capacitor; some while ago I restored an old Tek 545 scope, one of its main filter caps was now a nice 2k resistor! I de-capped it - dug out the rubbish and recapped it with new Nichicons, I was happy with the results. I left a note inside the unit for later to remind me what I did.See reply 33 and 34 of the below post.https://www.eevblog.com/forum/repair/restoration-repair-of-tektronix-545/25/

author: neo
author_rank: Super Contributor
timestamp: July 09, 2017, 08:16:33 am
content: Quote from: VK5RC on July 09, 2017, 01:19:27 amInteresting and good idea on the capacitors, looks matter as much as performance. I am indeed making progress but i have reach a point where i have no clue what to do really do. I mean i was always kinda lost but i think i may be in over my head with this one.The display is capable of being fully lit, as it is if reset is held or if it is in the 250MHz-18GHz range.All power rails check and no card is loose that could cause this, lightly tapping it affected nothing. The best the manual has to offer is troubleshooting methods which go into bcd codes, logic probes, comparators, etc. Just trying to figure out how to do any of that has my head swimming, let alone the thought of actually doing them.Not to sound snobbish or anything but a 3 digit display is more than a little annoying .

author: VK5RC
author_rank: Unknown
timestamp: July 09, 2017, 12:00:38 pm
content: Am I correct in my understanding that it can display a count (semi-accurately or not) in either low or high range? Which input? Which resolution? Do you only get 3 digits ever?I have had a quick look at the manuals - to me the HP Journal gives a nice overview of how it works (or doesn't)http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1973-04.pdf.esp figure 11 on page 8or in the manual vgkid linked, figure 4-45 page 4-33Some years ago my 5342A had a stuck display (displayed the same rubbish always) - the CPU and CPU clock was working - could see logic flowing - was a 'stuck' logic node later down the path- biggest problem was getting access to the boards while on- I didn't have a set of the service extender cards. Took me a long time to find that $1 part!!!!

author: neo
author_rank: Super Contributor
timestamp: July 09, 2017, 05:39:07 pm
content: It will only display the same 3 digits in all ranges except 250MHz-18GHz in which they all light, but due to the fact the n connectors i ordered isn't here yet i can't test. In check and 10Hz-250MHz, the two which i have the means to test, are very accurate it almost gives my other frequency counter a run for its money. I say almost because i don't know which is more accurate. Also, the range switch works as the 3 digits i can see change value on;1 it reads .000 KHz;10 it reads 0.00 KHz;100 it reads 00.0 KHz;1k it reads .000 MHz;10k it reads 0.00 MHz;100k it reads 00.0 MHz;1m it reads .000 GHz:Now barring all possibility of a sane fix i might could live with this as it does allow me to see the frequency in detail though only in steps. Also it looks as if on 250MHz-18GHz it does not have this problem.

author: neo
author_rank: Super Contributor
timestamp: July 09, 2017, 09:41:09 pm
content: Quote from: neo on July 09, 2017, 05:39:07 pmI typed that in a hurry, i mean that if there is no sane fix it could be a problem that is possible to deal with. Also i think i might have a riser card that will work for this ill have to check.

author: Cubdriver
author_rank: Unknown
timestamp: July 09, 2017, 10:13:58 pm
content: I'm busy working on a friend's car right now (replacing a bad wheel rear wheel bearing, oh what fun!!), but will try to dig into the manual later to see if I can offer any suggestions. I believe that it suppresses the leading zeroes, so perhaps something is amiss with yours in that regard and it's, for whatever reason, suppressing all but the last three digits regardless of if they're zeroes or not.I'll be doing some troubleshooting on mine too, as it is totally unresponsive to any input. It passes self tests, but appears to have had its front end fried.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 09, 2017, 10:43:34 pm
content: Quote from: Cubdriver on July 09, 2017, 10:13:58 pmThanks for the update, yeah a wheel bearing what endless fun. So much fun i think i would rather lynch myself than do one, so you must have more patience than me. I had thought of that but hadn't put it into so many words so thank you for organizing that thought.

author: Cubdriver
author_rank: Unknown
timestamp: July 09, 2017, 11:53:03 pm
content: Quote from: neo on July 09, 2017, 10:43:34 pmLOL - it's not quitethatbad (this will be the third one that I've done) but I have given up for the night as I can't coax the hub nut off - used my 3/4" drive socket set for the previous two, but it's currently buried and inaccessible due to an ongoing home renovation. Started looking for a 29mm impact socket, but of course with my usual perfect timing found it online two minutesafterthe auto parts store that had it closed. I'll continue on that little misadventure tomorrow.In the meantime, I'm now off to poke and prod at the sick 5340A on the bench, and will look to see if there's anything obvious in the manual regarding the leading zero suppression.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 01:50:21 am
content: Quote from: Cubdriver on July 09, 2017, 11:53:03 pmSo what do you think, is there much hope for your subject?

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 02:20:16 am
content: If you want a laugh read on, i meant to buy 50 ohm bnc for my test bench and i wound up buying 75 ohm. It is in times like this that i feel really stupid.

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 06:45:15 am
content: Quote from: neo on July 10, 2017, 01:50:21 amI suspect something fried on the A22 board (the custom IC I mentioned in another thread about this counter), but am waiting on a just ordered extender card to be able to break it out and test it. This is where I stopped last time, due to the extender card I have being too long - there's a coax line feeding that board that's too short to let it go up as far as would be needed with what I have. Last time there were no shorter extenders listed on the bay and so it got lost in the shuffle. Tonight I found one; hope to have it by the end of the week.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 07:22:41 am
content: Could you do me a huge favour and look on your a-26 board and tell me what color wire #7 and 8 are? That is counting from the left with the wires in your palm, they are marked + and 5.Also i have proven two things very very clearly. The first is that i am bloody insane and the second is that the problem is NOT in A-26, i know because i de-soldered a-26 with no change.

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 07:28:43 am
content: OK no the problem HAS to be in A-26 it just wasn't solved by a lack of, i didn't read the schematic well enough on the first crack at it.Stop me if this is insane but what if, using appropriate resistors, i just tied pin 10 of the tubes high?

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 07:33:39 am
content: Also, as fair warning, i have started thinking of possible solutions entirely by myself so things may drift a bit on the crazy side.

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 08:09:11 am
content: Quote from: neo on July 10, 2017, 07:22:41 amUgh - Sorry, I was away from the computer.the '+' wire is redthe '5' wire is wht/grnThe board in my counter:And on that note I must hit the sack. It's a 'school' night (well, morning, since it's 4 AM.) Ugh!! Going to be dragging today!-Pat

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 08:18:04 am
content: Quote from: Cubdriver on July 10, 2017, 08:09:11 amThank you, i should have been paying more attention when un-soldering them but in my defense i was labeling them as i went i just got two confused.

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 08:20:03 am
content: A quick glance at the schematic before crashing shows that the blanking logic seems to come from U15 on the A24 board and is passed directly through the A25 on to the A26.This is probably a superfluous question, but have you confirmed the supply voltages to the A26 blanking board? You should have +175V relative to ground on the red wire, and +2V on the orange one next to it.I wouldn't go tying things to the 175V line just yet - it worked before, so it should be fixable once we figure out what exactly is amiss.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 08:39:04 am
content: Quote from: Cubdriver on July 10, 2017, 08:20:03 amthe +175 is +130 instead but it lit the entire display. Also i already tried my way and got nowhere.

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 09:05:16 am
content: A-26 is now back in place. Also a recap as i like to do to help get information organized.Red is +132 when it should be +175VOrange is +1.94 when it should be +2.0A-26 is not uselessA-26 is not directly the faultWhatever interfaces with A-26 is now highly suspect.It shows all digits lit when in UHF mode, or when reset is held.I did something mildly insane but didn't break anything.

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 09:27:41 am
content: At resolution of 100k in check mode1=4.522=4.423=4.424=3.825=3.89B=1.94+=132.the other set of 1-5 is not easily obtainableOnly the three not affected by blanking lit.UHF mode1=0.102=0.103=0.104=0.125=0.11B=1.92+=132.the other set of 1-5 is not easily obtainableAll lit.

author: VK5RC
author_rank: Unknown
timestamp: July 10, 2017, 10:23:19 am
content: I am not much help now,I have no doubt you will get this.A tip I got from a great Ham - before switch backon - go for a quick walk out of the room then re-check. If the part is really expensive, have a cup of tea first. Take lots of photos. Helps later when the labels fall off- don't ask me how......

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 03:29:28 pm
content: Quote from: neo on July 10, 2017, 09:27:41 amOk. It seems that the issue is upstream of the blanking board, as they unblank in certain circumstances. I was thinking of the fact that you said in reset all of them lit as I went to sleep this morning, and realized that bit of info likely clears the blanking board of guilt in this issue. I'll take a look at my schematics and take some measurements on mine later after work.-Pat

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 03:35:58 pm
content: Oh, and don't worry too much about the +175V supply reading 132V - I just looked at the schematics for the power supply wondering if you might be a bad filter cap in that circuit too (there isn't one), and found a note adjacent to the output.Note 4 - "THE +175V POWER SUPPLY WILL READ APPROX. 135V rms ON MANY VOLTMETERS DUE TO ITS HIGH RIPPLE"Sounds like that at least is pretty much right where it should be.-Pat

author: TheSteve
author_rank: Unknown
timestamp: July 10, 2017, 06:50:24 pm
content: I can confirm the Nixie supply voltage is fine. I believe the ripple is good for the tubes and done on purpose.

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 07:05:25 pm
content: Quote from: Cubdriver on July 10, 2017, 03:35:58 pmI figured it was but at this point i was running down all possible suspects. So whats the current theory of problem?

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 07:59:40 pm
content: Also, in 10-18GHZ mode , it is only three digits but it does read the frequency i put on it which unless im wrong proves that the non replaceable stuff is functional.

author: TheSteve
author_rank: Unknown
timestamp: July 10, 2017, 08:18:22 pm
content: Quote from: neo on July 10, 2017, 07:59:40 pmYou're inputting a frequency over 260 MHz or so to test this right?

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 08:27:32 pm
content: Quote from: TheSteve on July 10, 2017, 08:18:22 pmNot yet but doesn't the 10Hz- 18GHz mode uses the same circuitry as higher frequencies?

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 08:41:23 pm
content: Which input are you using - the Hi-Z BNC on the left, or the N connector on the right? The 1 megohm BNC input on the left bypasses a lot of the internal circuitry used for the high frequencies.-Pat

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 08:42:50 pm
content: Nevermind - 10Hz-18GHz means you must be using the 50 ohm N connector input. D'oh!-Pat

author: TheSteve
author_rank: Unknown
timestamp: July 10, 2017, 08:53:52 pm
content: I am under the impression the sampler can be dead and the counter will still work to 250/260 MHz or so. I believe the only way to know for certain is to feed a frequency above that range in.

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 09:04:35 pm
content: Quote from: TheSteve on July 10, 2017, 08:53:52 pmI guess i will have to see if my 608C works.Anyone got a clue about the 3 digit problem? If it ain't the blanking part then i am completely lost.

author: Cubdriver
author_rank: Unknown
timestamp: July 10, 2017, 09:43:15 pm
content: Quote from: neo on July 10, 2017, 09:04:35 pmMy guess is something in the blanking control circuit, but I haven't had a chance to dig into it yet.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 09:50:36 pm
content: Very few things are capable of genuinely surprising me but i have to admit, i am genuinely shocked. I got this HP 608c signal generator free at last years hamfest and i never got around to test it just simply because i didn't need frequencies that high. I plug it in for the second time in a year and turn it on, and the thing works perfectly except for the DBM and modulation percent meters. It is even accurate to its frequency gauge.Definitely not bad for something that had a tag that said, "Non-functional, please haul away."It will allow me to test the high end of this 5340A but i have another adapted coming so it will be a couple days.P.S. Anyone know where i can get a knob for the frequency control shaft? I can't use anything i got because its a big shaft. I found one on ebay but it is 40 bucks just for a knob.

author: neo
author_rank: Super Contributor
timestamp: July 10, 2017, 10:46:15 pm
content: Quote from: neo on July 10, 2017, 09:27:41 amOK a thought, if low the tubes light, i de-soldered a wire and tied that one point low and the tube lit BUT even with the tube lit it did not display properly.

author: neo
author_rank: Super Contributor
timestamp: July 12, 2017, 04:28:19 pm
content: After a couple days digging around in the schematic two things are the result,1)2) I know it can work but as near as i can tell it just doesn't want to use more then 3 digits for whatever reason, the blanking circuitry was suspect but near as i can tell it is ruled out because even if bypassed the it will not display anything other than 3 useful numbers all else being 0s.There has to be a reason for the absence of useful numbers above 3, the fact that it is only the 3 not affected by blanking annoys me, though i don't think i a smart enough to find it.

author: EPTech
author_rank: Regular Contributor
timestamp: July 14, 2017, 12:21:54 pm
content: Be careful when paralleling large filter capacitors over existing capacitors for testing. You may exceed the forward peak current capacity of the rectifier diodes, potentially degrading or destroying them. In these older devices they are usually over-specified, so I guess you are OK, but still, be mindful. Sounds like you are on the right way. I agree with my colleagues, recap the entire power supply and look for leaky (warm) tantalum capacitors as well.Happy repairing.

author: neo
author_rank: Super Contributor
timestamp: July 14, 2017, 07:20:20 pm
content: Quote from: EPTech on July 14, 2017, 12:21:54 pmAs of current the problem is so obscure i have no clue where to even look.

author: Cubdriver
author_rank: Unknown
timestamp: July 14, 2017, 08:17:13 pm
content: My extender card is presently still lost in the black hole that is the Philly Postal facility, so I haven't looked further at it. Will maybe peruse the manual tonight to see if I can gain any insight into what might be ailing yours.-Pat

author: bitseeker
author_rank: Super Contributor
timestamp: July 14, 2017, 11:41:07 pm
content: Ah, so I this is what got lost in Philly. Well, that's a bummer. I just got caught up on the thread.

author: neo
author_rank: Super Contributor
timestamp: July 14, 2017, 11:48:45 pm
content: Quote from: Cubdriver on July 14, 2017, 08:17:13 pmSorry to hear about the mail system getting screwed up.I had a couple of theories and using one of them i did manage to bypass the blanking but in doing so i disproved all my other theories.They blank the left 5 digits because they are zeroes, there is nothing reaching the display past the first 3 digits.I thought to myself, hmm maybe they blank the counter chips?Nope no connection to the any chip inputs, only outputs and with that i stopped thinking before i broke something.

author: TheSteve
author_rank: Unknown
timestamp: July 14, 2017, 11:56:09 pm
content: When you move the resolution slider does the decimal place move?

author: neo
author_rank: Super Contributor
timestamp: July 14, 2017, 11:59:10 pm
content: .000KHz0.00KHz00.0Khz.000MHzThat is what it does exactly, so in short yes.

author: TheSteve
author_rank: Unknown
timestamp: July 15, 2017, 12:03:10 am
content: Well at least that is working. Just as an FYI when you switch between resolutions(with no input) you can expect all of the digits to light up briefly before the blanking circuit disables all but the right most 3 digits.The more we determine works/doesn't work the easier it should become narrow down the fault.

author: neo
author_rank: Super Contributor
timestamp: July 15, 2017, 12:04:25 am
content: Quote from: TheSteve on July 15, 2017, 12:03:10 amIt does exactly that.

author: neo
author_rank: Super Contributor
timestamp: July 15, 2017, 05:11:53 am
content: Forgive me if this is impetuous but i am a bit too stoked to care.I WON!!! I WON!!!!! FOR ONCE IN MY LIFE I'VE WON!!!!Sorry i don't win a lot, now that i have got THAT out of my system. The high frequency counter works! It even gave me a big clue as to the problem elsewhere in the unit! Any number above the first 3 is a garbage number, in GHz mode they will light but are useless because they don't display correctly. In the 1M range they will not light at all past the first 3.Also Cub, would you mind telling me how to read the serial # so i can know the year for sure?

author: neo
author_rank: Super Contributor
timestamp: July 15, 2017, 05:46:01 am
content: Pictures.

author: Cubdriver
author_rank: Unknown
timestamp: July 15, 2017, 07:45:41 am
content: The instruments made after 1960 have a two part serial number - 3 or 4 digits forming a date code followed by a dash (early units) or a letter (that seems to indicate country of manufacture for later units) and then another 5 digits for the unit's serial number.My understanding, which may not be 100% correct, is that the first digit (or first two, for four digit prefixes), when added to 1960, will give the year that production run started, and that the last two give the week it began. For example, the 1328A beginning on my 5340A would indicate mid 1973 production - 1960 + 13 gives 1973, and 28 for the 28th week. 'A' designates US made.A lot of the LCR meters were made in Japan; my 4262A starts with 2022J which would indicate 22nd week of 1980, made by Yokogawa in Tokyo.Some of the signal generators were made in Böblingen, Germany; they have a 'G' in the serial number.The thing I'm not certain of is the production week numbers, as I've seen instruments with late production week numbers (40+) that have semiconductors with early date codes from the following year. That's why I think that has to do with when a run started, but that the instruments may have been fabricated over a longer period.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 15, 2017, 07:52:24 am
content: Quote from: Cubdriver on July 15, 2017, 07:45:41 amWell with that convention mine was minted in 1978 BUT there a was a sticker on the front that said "M1973" when i first got it. So really it is at best a guessing game on this one. I thought they had all but completely switched over to leds by 78 though.Also the more i go into depth with the display issue the weirder it gets. Is it just my perception of it that makes it that way or does it seem fairly weird to you?

author: Cubdriver
author_rank: Unknown
timestamp: July 15, 2017, 08:14:04 am
content: Quote from: neo on July 15, 2017, 07:52:24 amI just looked through my catalogs. Surprisingly, they show and call out the nixies as the readout up to the 1982 catalog. The seven segment LEDs appear in 1983. Perhaps the switchover began during '82.I think your counting issue will wind up being simple once it's figured out. As is said in the other thread, I suspect the carry signal is getting hosed somewhere along the line, but I haven't dug in enough to how it counts to be sure.The older counters were pretty much literally daisy chained decade counters that counted input pulses for as long as the gate timer held them on. The timer would say 'start', and the conditioned input signal would clock the first digit, which would count from zero. When it reached ten, it would send one pulse to the second digit, which would increment by one. The second digit would pulse the third every ten counts, and so on, until the count time expired and the gate closed.Newer ones (and this one, I'm assuming) used more sophisticated methods that I'm not yet 'up' on, so I'm of limited help until I do some more digging on the operation.-Pat

author: Cubdriver
author_rank: Unknown
timestamp: July 15, 2017, 08:18:15 am
content: And on that note, I must cease my nocturnal ways and try to get some sleep, as it's after four am in these parts.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 15, 2017, 08:22:28 am
content: Quote from: Cubdriver on July 15, 2017, 08:18:15 amHope you get some good. Also yeah i think it will be quite simple once i "get it" but for now it is a very strange well defined phenomena.

author: bitseeker
author_rank: Super Contributor
timestamp: July 17, 2017, 04:22:30 am
content: I though the first set of digits was the date code of the design on which that particular unit was based. Not a big deal as neither interpretation nails down the manufacture date. You'd still have to find some component date codes inside in order to approximate that.

author: neo
author_rank: Super Contributor
timestamp: July 17, 2017, 04:28:19 am
content: Interesting update, in the 100k range it used to count 3 digits of the frequency for example (4)61.5 MHz the 4 not being visible as the left 5 digits were blanked but now it does the same thing with the junk numbers.

author: Cubdriver
author_rank: Unknown
timestamp: July 17, 2017, 07:13:55 am
content: Quote from: bitseeker on July 17, 2017, 04:22:30 amThat sounds like a plausible explanation as well. Thus far I've only seen early following year date code components in units that had high 'week' codes, but I admittedly haven't dug too deeply into that. I'll try to pay more attention from now on. It would be telling to find one with components that were a year or more 'younger' than the date code would indicate (eg 1975 parts in a 1973 coded instrument, rather than just early 1974 parts in a late 1973 unit) - I can't imagine that every instrument had a new design iteration every year.On another note, my extender card is on the move and has allegedly made it to Springfield, MA. At this rate perhaps I'll see it by Tuesday. <fingers crossed>-Pat

author: neo
author_rank: Super Contributor
timestamp: July 17, 2017, 08:13:37 am
content: Quote from: Cubdriver on July 17, 2017, 07:13:55 amGreat to hear it is on the move again. Is it a bit odd how on the 100k mode the 3 digits worked fine when i took a picture but not later? Possible clue.

author: neo
author_rank: Super Contributor
timestamp: July 29, 2017, 04:24:02 am
content: I have come up with a possible way to resolve the error without checking every single part, this idea is of course just a possibility and not intent. I could always get a newer one that isn't in great shape and the main boardsexcept display itselffrom it, because as near as i can there would be no difference except age.Don't worry about me killing oneyetto do that i would have to be able to buy another or find one inordinately cheap.As i said, short of just checking every little thing that it might be i am out of ideas. I get lost quickly when trying to understand the schematics.

author: Cubdriver
author_rank: Unknown
timestamp: July 29, 2017, 06:39:43 am
content: Mine is still sitting on the bench waiting for me to continue looking at it - I've been helping a friend do some painting and that has sucked up all my free time. Hopefully later this week I will have time to dig into the schematics and try figure out how the blanking works.This issue with yours still seems to me to be some sort of bad connection since it seems to work and then not work depending on its mood and the moon phase. That's aproblem to try to trace.-Pat

author: neo
author_rank: Super Contributor
timestamp: July 29, 2017, 08:19:52 am
content: Quote from: Cubdriver on July 29, 2017, 06:39:43 amYea i have definitely felt, might help if i was smart enough to understand the schematics but then again it might help if the schematics were on paper so i could actually work with them.The two screws on the display board that hold it in are missing so i take that to mean someone has tried to fix it before, which would ironically mean this problem is why it was so cheapANDfully functional except from the displayShort excerpt from my head."So it could be as simple as say, a single bad solder joint?Simple fix but it could take hours to find especially if it doesn't look obvious.Well are the card's loose?No the card's are not loose, i checked each one.Got any ideas?No do you?Let's try wiggling a card again.OK."Yes, i talk to myself. Don't all mad scientists?

author: neo
author_rank: Super Contributor
timestamp: September 12, 2017, 02:05:10 am
content: Well something interesting happened, i tried turning it on just to see the 3 digits work and it didn't do anything. Then later it was back to its normal state of semi functioning.

author: neo
author_rank: Super Contributor
timestamp: March 12, 2018, 01:30:14 am
content: A couple relevant bits, HP 1820-0986 is in fact directly replaceable with DM86L75N because they are one and the same.Took me an hour to find that out, and to find the datasheet.http://www.ralphselectronics.com/productimages/SEMI-DM86L75N.PDFDirectly relevant to my repair, IC#2 was replaced sometime post '93.

author: Tharkun
author_rank: Newbie
timestamp: June 01, 2021, 06:03:19 am
content: Hi it’s been a while now but did you end up solving this problem? I have exactly the same counter and it started doing exactly the same thing. Just wondered if you had solved it...Tim