Repair worklog : Old rusty HP 3458A

[TiN]

Thanks.
I got idea now that PAL is working.
Traced signal path of transmit...Signal after U700 ok, signal after U100F - ok, Signal on cap C104 - ok, Signal on CR104 anode - ok, singal on J102 optical transmitter - stuck high...
Loose my temper and shorted anode of CR101 to U302 pin 9 input on A3 A/D board. Guess what, it booted and let me to UI.
It does not sample anything except FREQ and PERIOD, but it could be just set on some hold or trigger manual mode, never used HP DMM before...

It does lit up ERR with next errors:

202,"HARDWARE FAILURE -- SLAVE TEST: CONVERGENCE"
110,"CALIBRATION REQUIRED -- ACAL"

Nothing else.

If I try run ACAL ALL, it says 205,"HARDWARE FAILURE -- CAL VALUE OUT OF RANGE: 72"

Update, it's TARM command, now it's sampling...

Update 2: Doh, interface of 3458A definately not for bench use from front panel, user unfriendly  Yah, I got spoilt with Keithley dual-screen display and menu system...

[TiN]

LA capture:



Photo of dodgy test setup: Note ground and white TX line from A6 to A3.



UI photos:




Time to go bed, 3:57 AM, again. But got some direction, that's hope. ADC working, digital A5 working, now fix optical issues (transmitter/receivers are easy to buy from Digikey) and will be time to debug A1 DCV board.

[OldSchoolTechCorner]

Did just get mines today and did come with voltage reference board. Here a quick inside look before restoration, already found couple issues.










Corrosion on leads







Claim to be defective, will check later, is open, or shorted windings, before assuming. As could just be a power supply issue.







Not as bad as I was expecting, sure clean up nicely







Looks like one issue.

[Vgkid]

Looking forward to the flood of 3458a repairs...

[TheSteve]

Looking forward to the flood of 3458a repairs...

Hmmm, "flood" - no pun intended?

[Dr. Frank]

To both of you, TiN and OldSchoolTechCorner,

I'll keep my fingers crossed, that you both succeed in repairing your 3458As.

What you are doing, is really a tough job, nearly like building it from the scratch..

If any comparison to a working unit is needed, just raise your hand..

Frank

[Vgkid]

Looking forward to the flood of 3458a repairs...

Hmmm, "flood" - no pun intended?

pun intended
:hide
 

[TiN]

Yeah! Congrats on your toy arrival, it does indeed look like less cleaning required

 Those burnt zeners are likely indication of dead xfrmr, as they sit straight on output winding. I added detail and measurement results comparison on my xfrmrs in article.

Your A5 board newer, wonder why there is X on ROM chip.
But same as mine , A5 date codes not matching analog boards, so likely was swapped.

 Drop me your address in PM, i'll send you some capacitors for A6 and zeners for A4.

Dr. Frank

Thanks! All of people posting here motivate us to do all this stuff. Best community, ever. Hey, i spent almost 3 years from time to time, reversing Keithley's 4 layer analog brd, this is piece of cake

We just hope for easy repair, like replace diode and 7815 and everything ok , lol. But not the case, this units take some sweat, that's for sure.

I bet seller reading all this and having great fun too. Join the forum, reveal yourself. We can help sell rest of rusty 3458A inventory in no time

[OldSchoolTechCorner]

Yeah! Congrats on your toy arrival, it does indeed look like less cleaning required

 Those burnt zeners are likely indication of dead xfrmr, as they sit straight on output winding. I added detail and measurement results comparison on my xfrmrs in article.

Your A5 board newer, wonder why there is X on ROM chip.
But same as mine , A5 date codes not matching analog boards, so likely was swapped.

Going to pull it later, looking at burnt zeners, output winding more likely overheated in the process and is more likely shot measure it later once finish with other project. I was wondering about the X marking, will soon enough find out

[Macbeth]

Yeah! Congrats on your toy arrival, it does indeed look like less cleaning required

 Those burnt zeners are likely indication of dead xfrmr, as they sit straight on output winding. I added detail and measurement results comparison on my xfrmrs in article.

Your A5 board newer, wonder why there is X on ROM chip.
But same as mine , A5 date codes not matching analog boards, so likely was swapped.

Going to pull it later, looking at burnt zeners, output winding more likely overheated in the process and is more likely shot measure it later once finish with other project. I was wondering about the X marking, will soon enough find out

It looks like yours is in better nick than TiN's was. You got a ref board at least (with insulating cap - have you checked what version of LTZ1000/A you have in there?)

TiN has a very nice VFD while yours is unknown at this point. I hope it's a goodun 

[TiN]

Seems like A3,A1 boards are much older on O's unit, datecodes 1988 (!).

There is interesting difference, on A3 A/D board, his board have U213 populated, while mine and photos on web of newer A3 boards show no chip there and a jumpwire from pin 8 to 10.
Chip location near 20MHz oscillator in center of board..

Swapped receivers on A3 board (used external trigger one ) - now optical interface works fine. It was a receiver U301 dodgy..

[ManateeMafia]

I have seen the same missing part. It is not noted in the CLIP IIRC. It doesn't seem to have an effect on the board and its removal may be part of a service note from HP. They mentioned having to swap out A3 boards for issues with the rundown conversion here ... http://cp.literature.agilent.com/litweb/pdf/3458A-07B.pdf

[TiN]

Yes, I saw it, as well as all other service notes

Yesterday was first time I ran out of hooks for LA... :



And that's correct. Only hardcore, only oldschool, using by bodge to generate UV for UVEPROM erase, so I can flash latest 9.2 firmware.



Next steps:

A1 DC board debug.

Symptoms:

DCV (any range) reading as near zero, but should be bouncing around on 10VDC and lower as it's >10GOhm impedance. So something somewhere cause too low impedance/short.
Ohms reading near zero for 10K and higher ranges, but OVLD for lower.
Current reading something microamps

ACAL gives error - out of range for constant 72, which is dcv gain 10V

Also how do I disable pesky BEEPs on every keypress? If I enter BEEP OFF and press enter, it just beeps once, go back to measurement and nothing changes, still beeping. 

[ManateeMafia]

I think I have seen you use that light before 

Service note 18A mentions short term drift correction. Maybe a 10V cal needs to be performed so it knows what the new reference voltage is? I would think it would be happy then.

I don't know if the beeps can be disabled without running some wire and a toggle switch....

Do you still have a missing jumper from header P100 next to the reference board. I was looking at your pictures and it looks like a jumper is missing. I have a jumper installed between Normal pins 2&5. It is also there on my burnt A1. Schematic shows it as signal DC_AD from J2.6

[Zucca]

I wonder if that plastic brush will create some dangerous ESD crap...mmm probably not in water... for a few dollars I got an ESD brush... don´t know if it was necessary but better to be safe than sorry.

Anyway, another TiN masterpiece. It is like watching some alpinist climbing the Everest.

[TiN]

 

TiN -> Doh!



Next time I come by Florida, I'll buy you any drink you want 
I mean, there is not zero chance that I could spent days of debugging instead of popping that jumper in, as I'd rather think about some complicated problem on component level, instead of checking multiple photos of other 3458A boards I saved on drive all these years...

Measuring +10.0006 VDC from SMU:





Ohms mode





DCI ranges 10nA, 100nA, 1uA, 10uA, 100uA showin zero, no matter what current supplied into meter. So those ranges are broken. That cause self-test fail on value 95 as well.
DCI ranges 1mA and up are fine.

True people say - one set of eyes is good, but fresh eye always better 
So happy now.

Video with Self-test, ACAL attempt and some tests.



Firmware 9.2 is in the unit.

Current range should be relatively easy fix from now on. I'll leave it for tomorrow...

P.S. As much as 3458A awesome in terms of performance, I think that's much it's HORRID in front-panel operation. I used it for two days, but already hate it.
I mean really, it's hard to remember all those paths and combinations. I understand the target group of 9500$USD multimeter, but still. Now I completely understand why instrument like Keithley 7510 would be much better choice for bench use, if one does not need performance of 3458A.

[TheSteve]

Top work TiN - nice to see there is a pulse and it is almost fully back to life.

[macboy]

Very nice work 
Are you still hard-wiring to bypass the fiber optic isolation?

[HighVoltage]

I understand the target group of 9500$USD multimeter, but still.

May be more .... What is wrong with this dude, asking US $15,600.00
http://www.ebay.com/itm/Keysight-Agilent-3458A-001-002-Digital-Multimeter-8-Digit-/141587046591?hash=item20f73ee0bf

It is really nice watching you in fixing this great instrument.

[Jwalling]

I understand the target group of 9500$USD multimeter, but still.

May be more .... What is wrong with this dude, asking US $15,600.00
http://www.ebay.com/itm/Keysight-Agilent-3458A-001-002-Digital-Multimeter-8-Digit-/141587046591?hash=item20f73ee0bf

Same thing that's wrong with this guy:
http://www.ebay.com/itm/Tektronix-TDS784D-2M-2C-4C-/401003605849?hash=item5d5dad6f59

Or

http://www.ebay.com/itm/MAKE-OFFER-Tektronix-TDS644A-WARRANTY-WILL-CONSIDER-ANY-OFFERS-/221180496032?hash=item337f6288a0

"Testequipmentexperts" should know that that scope is crap anyway... leaky caps etc.

Jay

[TiN]

macboy

No, I stolen receiver from external trigger optical link. Will put new back in after order replacement from Digikey. For now it's ok.

[soren]

And that's correct. Only hardcore, only oldschool, using by bodge to generate UV for UVEPROM erase, so I can flash latest 9.2 firmware.

I like to use Winbond W27C512 EEPROM pulls, which are available for next to nothing on ebay/aliexpress. No need for improvised tanning beds :-)

[TiN]

Buying W27C512 : days of waiting
UV erase and program : 15 min
You choose

[TiN]

Since ranges 1mA and more working ok, we can rule out R210,R211,R212,R213 current shunt path, as well as input relays K201,K202,K203.



It is not likely that issue to be damaged JFET switches Q201-Q205 for low-current shunts R209-R206, as it’s less probable that all of them died.
So I will test control circuitry first, which consists of U204 and U205 LM339 comparator for level shifting, U203 4094 shift register and RP200 generic resistor network and CR205 zener.
One thing we know from initial inspection – resistor network RP200 was resoldered by previous owner. I have bought RP200 replacement before, just in case, so it could come handy.

I think the most difficult in this repair would be finding DIP-packaged LM339 and LM393  I did not used DIP parts for many years, and resist urge of bodging in SO-versions in there 
I do have MC14094BCP replacement, left from Keithley 2001 repair project, in case I would need one.



HP's CLIP listed LM339 comparator as SELECTED, what would they select in it? Offset voltage?

[pelule]

LM339 comparator offers Open Collector outputs.
As far as I could figure out, the HPs are selected for minimum level of "OFF" output leakage and a minimum "ON" voltage (Vce).
I had so far no isues with "general" LM339, thus I believe, this was a "for security" request.
Last but not least the custom chip marking (HP number).