Next repair, HP3456A (o; - Page 1
Forum section: electronics / repair

author: davorin
author_rank: Unknown
timestamp: June 11, 2014, 04:14:18 pm
content: Received a HP3456A multimeter today which I bought as "dead"...a quick look revealed that the fuse cap is missing...Opened up the top cover...released some screws on top and back...but can't quickly figure out how to get to the fuse holder itself to be replaced....

author: FrankenPC
author_rank: Unknown
timestamp: June 11, 2014, 04:31:38 pm
content: Quote from: davorin on June 11, 2014, 04:14:18 pmOn one of my repaired 3456's it arrived with a blown fast-blow fuse in the in-guard analog section. Easy to replace with a solid state fast blow fuse.

author: davorin
author_rank: Unknown
timestamp: June 11, 2014, 04:38:04 pm
content: My main problem is currently that I can't seem to find a way to remove the top/bottom covers in the back where the AC inlet and fuse holder is...Do I have to remove to whole back panel?

author: FrankenPC
author_rank: Unknown
timestamp: June 11, 2014, 05:03:05 pm
content: Quote from: davorin on June 11, 2014, 04:38:04 pmYou have to remove the large top and bottom panels. There is a single #2 phillips screw in the center of each main panel that is fixed in place. As you twist that screw, the entire panel moves backwards. After you get them off, unscrew the small aluminum guard plate and the fuse assembly is fully exposed.

author: davorin
author_rank: Unknown
timestamp: June 11, 2014, 05:12:29 pm
content: Hmm..not sure which aluminum guard you're referring too...I have here a metal sheet going from top to bottom with the fan attached to its back...

author: FrankenPC
author_rank: Unknown
timestamp: June 11, 2014, 05:39:47 pm
content: You have a variation of the 3456 I don't have. I don't even have a fan.

author: davorin
author_rank: Unknown
timestamp: June 11, 2014, 05:43:48 pm
content: Sad thing is that assembly/disassembly is nowhere mentioned in the service manual...Guess I need to go for the total disassembly then...but not this evening anymore ;-)

author: MadTux
author_rank: Frequent Contributor
timestamp: June 11, 2014, 07:12:02 pm
content: There's a big screw on each corner of the frame. Remove those and you can pull the whole rear section out. Then it's easy to find the screws you need to remove

author: davorin
author_rank: Unknown
timestamp: June 12, 2014, 10:40:32 am
content: Had to remove more than just those 4 screws...the side panels and handle needed to go as well...Now got the fuse holder removed for replacement...BTW: What type of use is used in the 3456A? Fast, slow?

author: davorin
author_rank: Unknown
timestamp: June 12, 2014, 11:22:41 am
content: Replaced now and powered on...Just display "------", regardless what measurement....Pressing test shows "-3.00000" though...

author: MarkL
author_rank: Unknown
timestamp: June 12, 2014, 02:26:04 pm
content: The "------" and "-3.00000" matches the description in the service guide in section 8-A-34, "Outguard Isolation Logic", on page 8-A-17 (rev B of the manual). There are step-by-step troubleshooting instructions there, but you will need a scope and signature analyzer for many of the tests.And for the fuse, the manual says it's HP part 2110-0033 for 120V operation (0.75A), and 2110-0065 for 240V operation (0.375A). Those are unfortunately obsolete with no cross-reference.For whatever it's worth, there's a Littlefuse 312 series 0.5A fast-blow fuse in my 3456A operating at 120V, but I've never replaced it. It looks old and original, but there's no telling for sure if someone else replaced it long ago.

author: FrankenPC
author_rank: Unknown
timestamp: June 12, 2014, 02:37:24 pm
content: Quote from: davorin on June 12, 2014, 11:22:41 amThat error is common. It could be either in-guard OR out-guard logic boards. Most of the troubleshooting can be done with a multimeter to find out exactly where the error is coming from. I purchased a $50 HP3456 as a donor unit to swap out the boards.

author: davorin
author_rank: Unknown
timestamp: June 12, 2014, 04:32:41 pm
content: Now pressing "Test" doesn't show -3.00000...but instead nervous display flickering...mostly blinking 0.00000 0...and some relays can be heard clicking...Looking at the inout/output of board A3 it looks like input signal gets distorted on the way...

author: davorin
author_rank: Unknown
timestamp: June 12, 2014, 06:09:55 pm
content: Hmm.....almost 3v ripple on A30 inguard 5V rail....What puzzles me though is the fact, that with in/out shorted on A3 outguard board, selecting test nbr. (TEST, 3, STORE, 5) 3 isn't possible...but resets the device...

author: FrankenPC
author_rank: Unknown
timestamp: June 12, 2014, 06:15:51 pm
content: Quote from: davorin on June 12, 2014, 06:09:55 pmFYI: Another problem I had was the front panel malfunctioning. There's not much going on with the front display/button assembly. So, I surmised the ribbon cable was corroded or had a mechanical connector failure. Regardless... my donor unit to the rescue!

author: guido
author_rank: Regular Contributor
timestamp: June 12, 2014, 11:29:34 pm
content: The ripple is bad obviously, the powersupplies need to be good before further trouble shooting.Whatcouldals be a problem are the roms. They fail a lot, meaning part of the contents get doggy. I had a 3456a that reset ok, but froze when selecting a specific function. The part of the rom with the routines for that function failed.So it might well be that the rom rot affected the routines for the test function in your unit. I succesfully replaced the roms.But first fix the supply (first thing i did was replace the caps).

author: davorin
author_rank: Unknown
timestamp: June 13, 2014, 08:03:56 am
content: C5 had around 1.4uF...5V rail is stable now...Displays now 00.00 after power up....though applying 1.5V results in "OL"...Most of the key presses are ignored and sometimes it won't return form test mode....Glad I have some old EPROMs lying around and recently bought a programmer...though just one 27C64 left...seems I have to retrofit my 3456A to the 27C256 version...

author: Wh1sper
author_rank: Regular Contributor
timestamp: June 13, 2014, 09:42:48 am
content: Quote from: davorin on June 13, 2014, 08:03:56 amI do have some spare eproms lay around, I wouldn't care about to give you a few.

author: davorin
author_rank: Unknown
timestamp: June 13, 2014, 09:00:37 pm
content: I go for my 27C256 version as the 27C64s are not pin compatible anyway...Stupid me I threw away all my UV erasers (o;

author: davorin
author_rank: Unknown
timestamp: June 19, 2014, 04:48:13 pm
content: Replaced now the 3 * 2564 ROMs with a 27C256....still same behavior as before..nothing changed...After power-up following is displayed for a few seconds:Code:--.---- -3And then:Code:- 00.00Several minutes after the display changes then and displays all sorts of numbers...

author: MadTux
author_rank: Frequent Contributor
timestamp: June 20, 2014, 02:19:48 am
content: You have at least one fault on the left digital side of your DVM. The 3456A, in contrast to the 3457A, that only displays an undefined "failed" message, boots fine ("3456A"; "AddXXX 0"; "------ ") if the analog boards are disconeced (4 pin connector on the bottom CPU board) or inexistent. It just has a blank "------" display and gives an -3.0000 error during self test.So if you already have replaced the ROMs and if there isn't any excessive ripple on the +5V rail (big blue cap, IIRC), the next probable cause in my opinion are the RAM chips, especially if those gold capped MOSTEK 4118 are used. Apparently they were made before the problem of gold/aluminium intermetallic was known.http://en.wikipedia.org/wiki/Gold-aluminium_intermetallicOne of those chips also failed in a 3456A that I got. Out of curiosity I removed the lid with a heat gun and analysed the chip under the microscope, where I discovered the gold wire bonding onto aluminium pads. Now after 35 years, solid state diffusion had enough time to happen and AuAl intermetallic formed between the bonding wire and the pad and vibrations, e.g. during shipping caused some cracks that killed the chip.I still have it, so in case I will get a good microscope with microposition probes once, I might measure the resistance between the pads and the chip leads and see whether I was right.P.S. I live near you, so in case you get pissed off too hard with it, I can give you (in exchange for the bad boards and a really big box of beer or 50Fr) a known good digital section of the 3456A.

author: davorin
author_rank: Unknown
timestamp: June 20, 2014, 08:13:40 am
content: Hmm...found some old 6116 RAM chips here....though twice the capacity they are pin compatible except pin A10, which is the latch enable signal on the 4118, though tied to Vcc. So it doesn't use the synchronous method.In worst case I have a 2nd 3456A which is working to swap out cards...though installed in my bookshelf and hard to remove as 2 * 6632B are on top of it (o;#define near_you ? (o;

author: MadTux
author_rank: Frequent Contributor
timestamp: June 20, 2014, 09:57:19 am
content: Quote from: davorin on June 20, 2014, 08:13:40 amEastern Switzerland

author: davorin
author_rank: Unknown
timestamp: June 20, 2014, 10:00:57 am
content: Ah my old "Heimat" (o;Lived a loong time at Lake of Constanze...

author: davorin
author_rank: Unknown
timestamp: June 20, 2014, 01:37:03 pm
content: Hmm..directly replacing the MK4118 with 6116 doesn't work....no display at all now ;-)

author: MadTux
author_rank: Frequent Contributor
timestamp: June 20, 2014, 01:52:06 pm
content: Quote from: davorin on June 20, 2014, 01:37:03 pmNo problem, I did that work for you.In the attachment is the RAM adapter I designed for the 3456A, it uses a SMD CXK5816http://www.datasheetcatalog.com/datasheets_pdf/C/X/K/5/CXK5816.shtmland some resistor-diode logic to combine the separated address bus of both MOSTEK 4118s into one.CXK5816 is pin compatible with the 6116, as far as I can see.You can also permute the address lines as well as you can permute the data lines between each other for easy routing, since nothing is stored in ram initially.Schematic is a slightly chaotic eagle file, but it might help you to design an adapter yourself. I used a 10k resistor, IIRC.

author: davorin
author_rank: Unknown
timestamp: June 20, 2014, 05:04:39 pm
content: A really weird schematic you have (o;You tie /CE to VCC via R1?Though in the layout you have /CE fixed to GND.Wonder why the 6116 chips are not working out of the box, as they can be connected 1-to-1 leaving A10 tied to VCC, which doesn't hurt at all....Let's see what other RAM chips I have collected over the years...

author: MadTux
author_rank: Frequent Contributor
timestamp: June 20, 2014, 07:17:42 pm
content: No idea why the 6116 doesn't work, if it's plugged directly into socket, A10 is on 5V => high, thereby no floating pin, see no reason not to work.Maybe it's too fast. I had that too, when I replaced the ROM with a new 70ns one. Old 150ns 27C512 worked fine though. The CXK5816 I use is a 150ns modell. Original Mk4118s are 200nsMy circuit:Package of CXK5816 in schematic was just a part that matched the CXK5816 pinout, so just look at pin number and signal name.Both MOSTEK 4118 /CS lines are put onto N-doped side of a diode. P-doped sides of diodes are connected together to /OE of CXK5816 and pulled high by 10k resistor. (simple AND gate)So if both Mk4118 are disabled, both /CS are high, =>no current trough diodes => /OE of CXK5816 is high => CXK5816 disabledIf any of both Mk4118 /CS lines is pulled low, diode acts a 0 Ohm resistor (with a slight voltage offset caused by the PN junction, but still logic low) and pulls the /OE of the CXK5816 low, thus enabling the chip (need to disable it when reading data from ROM or IO).Futhermore the /CS lines of the Mk4118 are connected to the theroretical MSB address line of the CXK5816 (practically you can use any address line, because mathematically the same, writes then to addresses mod 2, 4, 8, 16 etc.), thereby banking the memory. (Low address range 0-1KByte: /CS1=0 /CS0=1, High address range 1-2KByte: /CS1=1 /CS0=0)

author: davorin
author_rank: Unknown
timestamp: June 21, 2014, 01:57:39 pm
content: Found the bugger (o;A fine hairline on the bottom side on one of the RAM chips..shorting A1 and D7...Now I can switch between Volts, Ohm, but the display shows ".OL" and then after few seconds it shows the voltage correctly....then hearing a relay and it shows ".OL" again...So it is almost fixed now ;-)BTW: I wanted to test with the board from my other 3456A, but that one looks newer...just one ROM and one RAM chip....Letting it run now with a 12R resistor connected....shows correctly "12.145"....and suddenly switches to "026.00", then to "679.00" and then back again to "12.145"....

author: davorin
author_rank: Unknown
timestamp: June 21, 2014, 02:44:58 pm
content: Ah okay....test number 4 fails...showing "-4.00000" on the display...

author: davorin
author_rank: Unknown
timestamp: June 21, 2014, 04:42:01 pm
content: Debugging now the ADC section....When shorting the input with jumper 29 to GND, it still displays the "Overload"....when shorting the input to +5V DC, then "0.0200" is displayed...Attached a picture when applying a 1.5V battery to the front terminal, with auto-range off, and range set to 10V DC.Upper trace is TP402, the integrator output...lower trace is TP401, the ADC input...

author: davorin
author_rank: Unknown
timestamp: June 25, 2014, 02:47:42 pm
content: Hmm...after few days when powering up my 3456A seems to measure again normally....also hammering on the PCB with a screwdriver doesn't show anything...Anyone experienced some thermal problems with some OP-Amps?At least I have ordered now some LF356 (LF351 weren't available) and some LM101AH in TO package...Picture below shows TP402 (top) TP303 (bottom) measuring a 12R resistor....

author: davorin
author_rank: Unknown
timestamp: June 25, 2014, 05:21:53 pm
content: Doesn't seem to be a thermal problem....works for a while, then not, then work again....Below two screens with TP402 on top and the amplifier input Q311...Both dumps show the output when measuring a 9V battery on the 10V range...First dump is normal, second dump is when it just displays "OL"....

author: FrankenPC
author_rank: Unknown
timestamp: June 25, 2014, 05:36:05 pm
content: Isn't there a problem with the spring loaded board interconnects causing spurious disconnect issues? Are the gold connector plates bolted down or held down with rivets?

author: davorin
author_rank: Unknown
timestamp: June 25, 2014, 05:56:22 pm
content: No screws as in my other 3456A, just black plastic rivets...As you mention it....lifting the 3456a up a little and drop it on the table displays the "OL" again....some more lifting/dropping displays the voltage again...Guess I have lots of spare LF356/LM101AH then (o;Is there a place where people can post/lookup what faults were discovered and how it was fixed per model?

author: FrankenPC
author_rank: Unknown
timestamp: June 25, 2014, 07:50:48 pm
content: Quote from: davorin on June 25, 2014, 05:56:22 pmNot that I know of. But that doesn't necessarily mean anything. I did get some REALLY useful tips in this thread:https://www.eevblog.com/forum/testgear/hp3456a-service-notes-for-owners-info!/msg144820/#msg144820There is an attachment in the top post which has a bundle of service notes that may help.

author: TonyGreene
author_rank: Contributor
timestamp: June 25, 2014, 09:08:18 pm
content: If you can narrow it down to the bad board, I may be able to help. I have a parts unit I keep, that the A20 Input/Switching board is bad. All the rest of it is OK.

author: davorin
author_rank: Unknown
timestamp: June 25, 2014, 09:40:12 pm
content: Hi TonyI probably didn't understand you correctly....you have a 3456A to sell also with a non working A20 board?

author: davorin
author_rank: Unknown
timestamp: June 26, 2014, 05:51:14 pm
content: Hmm..replacing the rivets with screws hasn't brought the success I hoped....still displays overload sometimes....Started resoldering the analogue board now...or the AC converter...as it displays error "-9" when pressing TEST.Must be some interconnect missing from the logic to analogue board as I saw few times that no input relay was switched on at all...leaving the ADC floating....

author: davorin
author_rank: Unknown
timestamp: June 26, 2014, 06:07:04 pm
content: But much better now...lifting each side 5cm and let it drop on the table it doesn't show "OL" again...Only error "-9.00000" is constant now....some AC offset error apparently...

author: MadTux
author_rank: Frequent Contributor
timestamp: June 26, 2014, 09:23:36 pm
content: BTW, you can get the value of the error:get into 6 digit mode by: '6'; 'store'; '9'-ndigits (not important for this test)Goto test mode and press 'test number' in this case 9, 'store' and then '5'Good value for test '9' is +0.005One of my meters has that fault too, but it can miraculously eliminated by switching to the rear input, somhow only affects the front input.

author: davorin
author_rank: Unknown
timestamp: June 27, 2014, 05:31:08 pm
content: Shows "+14.25" for me....seems too bad (o;And what's even worse...still haven't found the cause for the "OL" error....I let it run during the night....and in the morning it had the "OL" error again....Lifting and dropping the 3456A doesn't produce the error....Guess I need to resolder all affected boards now...

author: davorin
author_rank: Unknown
timestamp: June 29, 2014, 10:15:01 am
content: Resoldered the whole analogue board now..and seems to stable so far (o;Interestingly the AC self test shows also different values for front and rear panel...Front: +9.979Back: +0.020Selftest runs successfully when choosing the rear panel (o;

author: davorin
author_rank: Unknown
timestamp: June 29, 2014, 01:56:06 pm
content: Hmmm..driving me nuts this 3456A (o;Putting all together and installed the metal covers...now again error "-4.00000"This time no "OL" display....just some floating voltage displayed...and hear no relay clicking...Ordered some Intel 8243 peripheral extender which drives the relay transistors....

author: davorin
author_rank: Unknown
timestamp: June 30, 2014, 09:02:12 am
content: Seems my last post was lost yesterday...Finally found the bugger as I investigated why sometimes the relays are not switched between 10V and 100/1000V mode...First I suspected the Intel 8243 peripheral extender, but found out the the PROG pin was floating from time to time.I could then track it down to the red and bad IC socket for U13 on the A30 board as pin 25 of the 8048 microcontroller didn't made contact.Just need to figure out why the selftest reports "-9.00000" when the front panel is active, but not when I switch to back panel connectors (o;