HP 3468A does not complete self-test, the LCD display all on. - Page 1
Forum section: electronics / repair

author: StrayElectrons
author_rank: Contributor
timestamp: December 08, 2024, 08:49:25 pm
content: Hi here, First time posting.S/N 2137A02728 and also the battery option 001 but I'll leave this battery's board disconnected via the ribbon cable at motherboard's also the lead-acid battery removed. No leaks luckily.I do have 5V (4.99V), +15V and -15V and ">7V" is around 12V.The LCD display is all on including dots and commas as well instantly at turn-on. Didn't exit the self-test. Posted this picture.I'm aware of basics to check for but I wanted to post here to get your thoughts. I know this model does have ROM IC that usually develops bit-rot but wanted to check anything else first then suspect the ROM last.I do have multi-meter and scope but I have to clear my crowded bench first.Cheers,

author: cruff
author_rank: Regular Contributor
timestamp: December 09, 2024, 01:13:21 am
content: That's the indication that it hasn't exited the self test, as you surmise. Do you have a copy of the service manual? It's available from several sites with a search.Section 7-D-14 Self-Test says the order of the tests is ROM, RAM, cal RAM then the A/D converter. If all of those pass then the "SELF-TEST OK" message is displayed.7-D-21 is the turn on failure trouble shooting section, there's lots of checks in that and the following sections to narrow down what might be wrong.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: December 09, 2024, 09:47:01 pm
content: It would be in your best interest to check out the rifa caps at the iec connector as well. NFM youtube video with replacement caps for a 3478a has link I used digikey carthttps://www.digikey.com/short/72j411bn

author: StrayElectrons
author_rank: Contributor
timestamp: December 09, 2024, 10:39:53 pm
content: Thanks! Do you have the laundry list of items in text?Reason:Clicked this and got the message: Due to restrictions, we are unable to add this item to your orderCheers,

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: December 09, 2024, 11:29:50 pm
content: Sorry im working off mobile phone but I was able to cooy and paste web addrrss and it worked fine

author: StrayElectrons
author_rank: Contributor
timestamp: December 10, 2024, 03:16:01 pm
content: Hi,I think this has to do with you account with Digikey's.Do you have other way to export your list that is not dependent on account or list in text?Cheers,

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: December 11, 2024, 04:13:45 am
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author: StrayElectrons
author_rank: Contributor
timestamp: December 11, 2024, 06:27:59 pm
content: Hey, Thank you for the list of components.Cheers,

author: StrayElectrons
author_rank: Contributor
timestamp: December 15, 2024, 12:36:16 am
content: Update:All the voltages are good according to service manual including +/- 10V including buffered +10V, and three voltages 3.3, 2.2 and 1.1V on the pin 1, 2, 3 of the W501 for display. I do have capacitor ESR meter and these 5 electrolytic capacitors checks out, and all the silver axial capacitors are not shorted.This multimeter is early version (eg does not have CR520) and seems to test digital circuits using programmed routines based on SA1 or SA2 via dipswitch 6 or 7.SA1 (dipswitch 6 on) displays this way: LCD display flashing dimly every approx 1 second, means 1.3 second watch dog triggering on failure to reset the U504 IC on pin 2, which did repeatedly bounce the reset circuit for microcontroller U501 IC pin 4 cyclically. Switch dip 6 off, stable with this reset circuit is held steadily high with display all lit up.How this SA1 mode behaves make me to believe that display is not the issue,Could be either digital section is jammed by other D/A, or latch IC or corrupt ROM IC. I don't have resources to program new ROM IC have to ask someone to send me one for HP 3468A.How reliable are CD4076BE ICs are? These are part of digital bus and one of pin drives the watch dog counter. What about the SN74LS373N is these known to fail?Thanks and cheers,

author: StrayElectrons
author_rank: Contributor
timestamp: December 15, 2024, 08:39:49 pm
content: Finally dragged scope out and had a look.Checked clock and is beautiful sine wave, processor is working but 8 bit main data D0-D7 bus is horrible, slow rise but falling edge looks right and high frequency looking totally scrambled egg. The small bus 4 bit bus pin 20 through 24 are clean sharp TTL waveforms. Even I checked the latch IC U508 (SN74LS373) of input and output are also equally same garbage and U508 pin 11 is good nice waveforms.Do I suspect the LS373 IC?Cheers,

author: cruff
author_rank: Regular Contributor
timestamp: December 17, 2024, 01:11:43 am
content: Can you unsolder and lift one or more of the D7-D0 input pins to the 373 and see if those signals clear up?

author: fenugrec
author_rank: Frequent Contributor
timestamp: December 17, 2024, 01:25:08 am
content: +1, either the source of those signals is defective, or something else on the bus is affecting them. I think you're close.

author: StrayElectrons
author_rank: Contributor
timestamp: December 17, 2024, 03:13:52 pm
content: Lifting a pin I didn't thought of that! Thank you, certainly I'll try that, but it isn't socketed, have to cut a leg.Yes, I meant the inputs and outputs of this '373 are garbage. Enable pin is clean. The CD4076 in and outputs are clean. And other than processor's D0-D7 are clean signals.Cheers,

author: StrayElectrons
author_rank: Contributor
timestamp: December 22, 2024, 08:58:41 pm
content: I'm still on trouble shooting.The microcontroller is outputting bad quality signals, Slow rise to high but on turn off going low is sharp and nice.Does this HP3486A's microcontroller processor contains small ROM or just ram only? Can I use intel 8039 or must I find a MK36000 microcontroller? Which I cannot find MK36000 anymore on ebay.Cheers,

author: fenugrec
author_rank: Frequent Contributor
timestamp: December 22, 2024, 10:35:13 pm
content: Quote from: StrayElectrons on December 22, 2024, 08:58:41 pmHm, isn't MK36000 simply an EPROM ? In any case, the 8039 (also used in the 3478A which I have worked extensively on) has no built-in ROM or customization.If you have an EPROM reader I recommend you (carefully) make a backup of the ROM chip, I don't know if anyone has dumped it yet, and the 3478A is too different to have compatible firmware.

author: StrayElectrons
author_rank: Contributor
timestamp: December 22, 2024, 11:53:04 pm
content: My corrected.Edited again, Eventually found what I'm looking for on Intel D8039"-6" means 6MHz version.But did not find what I'm trying to find out what "AHL" suffix means for Intel D8039AHL?Thank you and cheers,

author: cruff
author_rank: Regular Contributor
timestamp: December 23, 2024, 05:54:40 pm
content: The service manual says it uses a 6.003 MHz crystal.

author: StrayElectrons
author_rank: Contributor
timestamp: December 23, 2024, 06:32:10 pm
content: I know because the service manual says this crystal is 6.003MHz.But the other datasheets for D8039-6 is not clear till I found another datasheet after few days of search answered my question about "-6" meant.The datasheet says intel processor without "-6" is rated up to 11MHz.But I'm still not sure what "AHL" means for D8039AHL?Thank you and cheers,

author: fenugrec
author_rank: Frequent Contributor
timestamp: December 23, 2024, 07:43:48 pm
content: Quote from: StrayElectrons on December 23, 2024, 06:32:10 pmFor the 8039 : apparently nothing, see screenshot. I wouldn't worry too much, just backup your cal, get a "new" 8039, socket it, move on. That is, of course, if you're sure there's not another device on the bus that is shorting the Dx pins and causing the weird levels.

author: StrayElectrons
author_rank: Contributor
timestamp: December 23, 2024, 10:24:06 pm
content: I rechecked and looked more carefully at data sheets and I'm now most satisfied with details I needed.All the parts ordered are turned pin sockets, LP8039AHL processor, 54LS373. Now I have to wait few weeks.Once I have parts, and replace these and if that fixes this, will let you all with new updates.Cheers,

author: StrayElectrons
author_rank: Contributor
timestamp: February 08, 2025, 11:26:22 pm
content: Parts orders came in while ago and had some time free, replaced two ICs with sockets, also 'LS373 and 8039 microcontroller, no luck, still same issue. Right now bit tired and can look again, tomorrow but I have other things like replacing parents' old generic but quality built by me computer from 2014 with new HP Z4 G4 one running windows 11 with all goodies.I have not heard from anymore about display issues staying on all on fixed with another display?Cheers,

author: cruff
author_rank: Regular Contributor
timestamp: February 13, 2025, 02:09:42 am
content: Well, you are left with one of U502 control ROM, U503 CMOS RAM or U503 HP-IL or the R568 resistor array as the remaining things attached to the data bus. Since the RAM is only attached to the D0-D3 lines, that isn't likely to cause issues on the D4-D7 lines it isn't connected to. Should be easy to eliminate R568. Since the the other ICs aren't in sockets (unless you did all of them), lifting a pin on U502 or U503 may help to narrow down the culprit.

author: StrayElectrons
author_rank: Contributor
timestamp: February 17, 2025, 12:59:56 am
content: Extracted R568 array and checked it and is good so put it back in. Pulled the HP-IL IC. No difference. Now I'm left with one to try is U502 ROM IC.The waveforms is not dynamic and eventually think my old goldstar 100MHz scope that I was given to me is not the best at high speed digital signalling even with a 8039 at 11MHz. Looks like I need an better scope.Is there a way to make 8039 free-run mode without firmware to see how this looks like?500MHz or 1GHz is out there but I have no idea how responsive to twiddlings and real-time waveforms, I know they are digitizing scope so bit of latency but how much?Ones I like to look at are these models using 68020-16MHz found in both Tektronix TDS7xx and HP 54542A, and 68030-32MHz in LeCroy scopes).I learned enough from researches, to not think about windows based scopes like the 54835A etc due to clunky user interface.Cheers,

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 17, 2025, 05:17:12 am
content: Your 100MHz scope is fine bandwidth wise for a 10-ish MHz signal, do you have a function generator or other signal source to test it on?Do you have your probe set to 10x and the 50ohm input setting turned off?If you are set on a new scope, I would look at a Rigol or Siglent for the modern feature set, and hackability to upgrade (buy cheaper base model and hack it up to the top model).From the two options you mention of HP or Tek, I personally am very partial to the Tek TDS700 series, but that's personal preference as much as anything.My Siglent SDS2104X HD hacked to 500MHz is much more capable (and smaller!) than my TDS784D and TDS794D in all but bandwidth.