Repair worklog : Old rusty HP 3458A

[TiN]

I will have full article on my site with summary on both money and time spent.

If have some ideas what to cover more, let me know

At this moment waiting for parts to arrive to continue.

[plesa]

Thanks Tin for this interesting story :-)
I will also replace all input relays, it does not looks like meter from metrology lab.

[Dr. Frank]

I see someone reading, great job

It does look like HP do overvoltage fan, unless they using 7815 in uncommon way by having low input voltage, perhaps?
I will definately take a measurement after new transformer installation.

TiN,

for a solution for that puzzle, simply look on the sticker of the fan!

As usual for fans, 12V DC is the nominal voltage only.

This Papst fan is rated for 6 - 15V DC!
Therefore, 15V is no over voltage.

So it will spin a little bit faster and will provide more air flow than at 12V, this will also be specified in the datasheet.
Also, HP has taken that into account, when they tested for proper cooling.
Don't change this 15V supply, when you buy the new fan!

Frank

[BravoV]

Regarding the 60mm x 25mm DC fan, I got tons of NOS "quality" fans laying around collecting dust, namely Panaflo and Sanyo Denki (all made in "Japan") not those Chinese crap.

Although not 15 Volt, all are 12 Volt rated, not sure if this rating is suitable for your need.

Here part of my stock to give you the idea what I have, its free if you still have trouble sourcing quality fan of that size.

PM if you're interested.

[Theboel]

I do not understand why a multimeter need an "overvoltage" run fan is the heat generated inside of 3458A is so high ?
in case the fan use for regulated the temperature inside the 3458A why they do not use a variable speed ?

[TiN]

Thanks for offer, but I already ordered NMB fan of same size and spec from Digikey

Dr.Frank

Just unusual to me to see powering fan from +15VDC. Not intended to change anything yet.

[TiN]

While typhoon DUJUAN unleashes it's wraith on Taiwan, I spend few more exciting hours scrubbing chassis from rust.



Aluminum inner frame have date code marks too, MAY 04 1995 and May 23 1995, confirming theory that all meter boards, except A5 outguard controller are ~1995 year, while A5 is was swapped out to older 1990 board.



IEC mains socket was fixed to chassis with rivets, I'll use suitable screws instead with new socket.



Was using sandpaper grit 200 first, then 400, then 600A. Few spots around nuts and corners still need some attention, will do it later before assembly.



Cleaned front panel from pesky stickers. It's almost mint now, satisfied with front face condition.



Cleaned keypad as well, who knows whose dirty fingers pressed teh buttons



So far spent ~2 hours on cleaning.

[LINACboy]

Had to replace the fan in my unit, too. The bearing was worn out and the balls were producing this painful grinding sound that instinctively makes you cross your legs...

My replacement fan is a Pabst Type 614 NGM (24V rated). It produces subjectively equal air flow (wet finger test) when powered by the DMM.

[TiN]

I wonder where did OldSchoolTechCorner disappear? He should get his rusty 3458A already, I believe. 

[ManateeMafia]

Great job on the cleaning. I like the idea of removing any trace of the previous users. It makes me feel like I am the original owner of a used car.

I had to replace a fan in a 3458A. It was old enough to be made in West Germany. I believe the replacement was a Papst 622L. Ebm-Papst had no records of my fan, they must have cleaned house a few decades ago.

[TiN]

My Digikey box just shipped. Let's see how quick it will come. 

[OldSchoolTechCorner]

Still around, just working on another project,"New workbench".

[robrenz]

Very nice restore work there TiN  keep it coming

[TiN]

OldSchoolTechCorner, I can't wait to see what's inside your unit.

While waiting for parts, I now took a close look on analog boards.

A1 board

This board also have mark "X" around reference header, also paper tape sticker "X" in center of board near RP7 resistor network. Visual inspection shows ugly soldering and flux around parts U300, U305, U301, RP300, U304, U306, RP301, U303, RP302, RP303, R308, R307, R310, RP200 and around all relays (K1, K2, K3, K4, K5, K6, K7, K9, K200, K201, K202, K203, K204). Relays have datecodes from 1997, while rest of the board IC's dated 1995-1996. Previous owner tried to fix board by replacing relays?

Looking not good, if you ask me. Those COTO relays, HP resistor network RP300 are unobtanium. U300 OPA111BM is rather expensive too, 50 USD a pop on Digikey.

I claim world-record highest resolution photos of 3458A stuff ever,  That's what happening, when photo-nut comes to volt-nuttery...

98MP, front side.



96MP back side.



Soldering "job"



Some people just don't know what they are doing in terms of repairs . That's why buying gear "after repair" sucks, often it's worse as than getting unknown, never serviced gear.

Rest of boards seem to be OK looking

A2 PCBA:



Rest of details on this board:



That piece of wire looks interesting, funky low-capacitance capacitor, perhaps?















A3 ADC PCBA:



Rest of details on this board:









Also another thing I noticed, guard traces are covered with soldermask. Isn't that defeat purpose of guard trace? Or it was an issue to manufacture with open copper in 90's?

[MadTux]

That flux residue usually dissolves easily in ethanol or isopropanol. Maybe resolder the questionable joints and then dump the board into a bucket/dish filled with EtOH or IprOH.

Are you using image stitching like hugin btw? That MC14094 shows some artifacs 
I usually use scanners to make board photos, they have more resolution and cost far less than good camera. My trashpicked Microtek Scanmaster i900 can do these resolutions in one shot.

[TiN]

I would approach zone area cleaning for such analog board, there are signals and isolation requirements, which are not forgiving treatment style "dump and wash all together", usual for popular digital stuff.
And I need get few bottles of clean IPA first.

[TiN]

Yes, just stitched together in photoeditor manually, 10 minutes for a set (4 photos each, 36Mp each, shot with Sigma Macro 150mm lens).
Scanners have crappy depth of field and unusable for shiny parts, like metal cans.  And they are bulky and obsolete 

[Macbeth]

Fantastic photos. Why I think I could even clone a 3458A from scratch, etching my own double sided PCB's from them 

Now those little blue "solder pots" buried in the PCB and the little white standoffs with solder posts on and the holes drilled all around them are especially intriguing. That stuff is total voodoo to me.

[ManateeMafia]

I'll trade you.... 

I bought this for future salvaging. The cables, relays, and resistors would cost a lot more than what I paid for it. Unfortunately, someone let out the magic smoke.

I have grabbed a few boards for the 3458A's. If you need a part or two, we can arrange something.

[TiN]

Should not be very hard, as all boards are dual-sided thru-hole only, unlike Keithley's boards 

Standoffs and leg-leg posts are due PCB surface is too leaky for those sensitive circuits. Even few nanoamps of parasitic current could easily upset operation, causing error in measurement and all random issues. That's why touching such with fingers circuits is a big no-no, as skin oil will cause unwanted current flows around. Teflon and air are much better insulators than FR4 PCB, so that's common practice for high-impedance circuit design.

ManateeMafia

Lol, I was looking on that one, wondering who snagged it. No wonder, who.
Hold it till I get solid test results and data on my gear. Work cancelled tomorrow as well due to typhoon, so no packages with parts tomorrow

[TiN]

More cleaning, this time outer covers.

This is what we had to deal with:



After a hour of scrubbing with scotchbrite, here's the result:



Few marks left in corners, will deal with that later before final assembly.



It start to take shape. I'd say improved condition from level 3-- to somewhat level 4.

Tomorrow should get some goodies from post. Can't wait!

[ManateeMafia]

It is good to see you made it through the typhoon.

I typically use Simple Green first and follow with alcohol. It looks like some of the plastic skin is peeling away from the edges. Do you think that the aluminum is corroded under the plastic? My calibrated 3458A has no plastic, somewhere before me someone stripped it off and painted the bare aluminum with an epoxy paint.

I asked the folks at Loveland about customizing the covers and they told me that they get some every once in a while. I think they said they got one that was painted red. I had another set of covers that were permanently stained from a sharpie, so I used Krylon Fusion paint. The color matches my old Fluke gear and made a huge difference in how it looked.

[TiN]

I'd love to see that. Graffiti 3458A anyone?  Gives +5 to precision feel. So folks on calibration lab don't usually give a dam about looks, as far as box works? That's nice of them.

Alu covers seem okay, it was just mechanical damage on corner, seems like.

Here's bonus for today. Exploded view of 3458A parts (except A9 reference board, so shown my LTZ ref instead as placeholder )



Better to view full-size on click.

[ManateeMafia]

 

This would make a good desktop background to replace one of my 3458A pics. Too bad one of my monitors just died this morning.... It looks like my to-do list just got bigger.

[Macbeth]

After a hour of scrubbing with scotchbrite, here's the result:

Ahh, yes, when tackling mundane cleaning tasks like this it's always good to have a bottle of beer or two to help relieve the monotony.

Now that Taiwanese beer in the top left corner of your pics, 95% alcohol  That's some mighty stuff!