HP/Agilent 34970A Teardown

[free_electron]

And another bites the dust.
A 34970A switch multiplexer with built in DMM ( 34401 style )

This one had all kinds of problems. The display was all garbled like segments lighting up together , the rotary encoder did not work quite right either and it kept coming up with errors at power up.

The front panel board

The bourns rotary encoder was at the end of its life i gueass. replaced it with a new one. Works fine now. These are mechanical encoders with a cheap plastic axle. i've seen many of these go bad..

The display was another thing... the darn driver logic sits under the glass... luckily it's a single row affair.


I simply bent the display upward. one of the drivers had shorted outputs. these are high voltage 32 bit shift registers made by TI that discontinued them a long time ago . They are now available from a company called SuperTex.  Luckily the local 'surplus parts' dealer had a bin of these so i grabbed a few for a dollar each. PLCC44. since there's only two of these i swapped both. After bending the display back  it works perfectly fine.

Powerup was intermittent. sometimes it would beep and no display , sometimes it would start fine.


THe problem was the semi-rigid flatcable between mainboard and display module. ( left cable above with the blue stripe) these are sincle strand ribbon cables that use a press-fit connector. they are horrible... contacts oxidize over time. so i unplugged it from its connector , pulled the top connector plastic off , put cable back in and soldered each strand to the connector pin. problem solved. works like a champ.

The brains of this thing is a 80196 with the same ASIC found in the 34401 multimeter. Actually this machine is nothing but a 34401 with a scanner front end. The analog section is housed in a plug in module.


Essentially the same guts as a 34401 mulitmeter. LM199 refernce diode and the same multislope asics. the problem with the module was a burned inductor ( left of the relays ) little TDK  choke at the current input. i guess someone must have overloaded it. The module has no fuses in it and relies on the fuses installed in the multiplexer boards... someone had replaced one with a stub of wire... and fried the meters input.


i got 3 multiplexer boards. 20 voltage inputs , 2 current inputs and 2 4 wire ohms inputs. each

the relay counters on some of em read extreme high numbers , like millions of actuations. i ordered these relays from digikey ( they're like 1.25$ each ) i need to swap about 10 in total. the other contact counters are all in the thousands range. these modules have their own CPU and EEPROM that holds the actuation count.

Machine is healthy again and works fine. Another addition to the 'pile'

[andyb]

Just wanted to thank you for posting these, love to look inside equipment like this. Man you run across some great stuff, wish I did!

[nanofrog]

You keep coming up with some wonderful finds. Any tips/tricks you care to share?

[retiredcaps]

Any tips/tricks you care to share?

https://www.eevblog.com/forum/chat/where-do-you-buy-your-equipment/msg141895/#msg141895

[free_electron]

Best tip : move to a high tech area.  That, or ebay. But beware. On ebay there are a lot of companies dealing in iued equipment that think they sit on gold ( they are... They buy that stuff by the pallet from govt surplus for 50$ and then flog it at 500$ on ebay ).

You can find better deals at the local surplus stores or equipment dealers.

If you know what you are doing you may want to buy broken stuff. But you need to know what you are doing. Don't go buying willy-nilly because it will become a money sink. Oh look there's a 8112 pulse generator for 100$ ... Yes indeed, but its got error 12. Grab service manual : first timing stage does not generate pulse .. Suspects are u200... U200 happens to be a custom hybrid that was discontinued 20 years ago... Pure unobtainium. So don't even go after that machine.
Oh , here's another on with error 22... Well that the pulse shaper that is fried.... Same story...

Sometimes broken machines are just beyond repair.

The other thing is your local newspaper. Look for businesses that flunked. That's where you get the real steals

[nanofrog]

Best tip : move to a high tech area.  That, or ebay. But beware. On ebay there are a lot of companies dealing in used equipment that think they sit on gold ( they are... They buy that stuff by the pallet from govt surplus for 50$ and then flog it at 500$ on ebay ).

You can find better deals at the local surplus stores or equipment dealers.

If you know what you are doing you may want to buy broken stuff. But you need to know what you are doing. Don't go buying willy-nilly because it will become a money sink. Oh look there's a 8112 pulse generator for 100$ ... Yes indeed, but its got error 12. Grab service manual : first timing stage does not generate pulse .. Suspects are u200... U200 happens to be a custom hybrid that was discontinued 20 years ago... Pure unobtainium. So don't even go after that machine.
Oh , here's another on with error 22... Well that the pulse shaper that is fried.... Same story...

Sometimes broken machines are just beyond repair.

The other thing is your local newspaper. Look for businesses that flunked. That's where you get the real steals

Thanks for the reply. 

I was thinking more in terms of location, or perhaps types of contacts I hadn't thought of (other than HAMB, university, or colleagues). Unfortunately, there's precious little where I'm currently living, so my only real source has been eBay.

As it happens, I've a 2445B on the way, and specifically asked the seller if it had any error messages prior to bidding (stated none), so hopefully, it will be OK (do plan to go through it; clean, check caps, ... sorts of things; seriously considering a fan replacement and a heatsink on U800 as well <gets rather hot & can die from what I've found online>). First time buying a used scope like this (off eBay), so I'm understandably nervous. Given what I've seen broken units going for, even if it's actually repairable, it's usually over priced from what I'm seeing. For example, a few had 04 errors on models that go for the same money as good ones. By the time calibration & shipping get added after replacing the chip (I don't have the equipment for calibration), it seemed too expensive to me.

Boy do I miss living in Orlando at this point (had resources there). 

[free_electron]

that chip needs a heatsink yes. if it dies it's game over.

Hamfests ... mm mixed feelings on those. It's invariably old crap with tubes , or some crufty HAM that thinks he got 'gold' and wants to flog it at exorbitant prices.

best sources are newspaper (flunked companies going in liquidation).

[nanofrog]

that chip needs a heatsink yes. if it dies it's game over.

Hamfests ... mm mixed feelings on those. It's invariably old crap with tubes , or some crufty HAM that thinks he got 'gold' and wants to flog it at exorbitant prices.

best sources are newspaper (flunked companies going in liquidation).

Good to know I need to go ahead and heatsink the U800.  Figured when the fans die, the U800 cooks itself to death (but if the fan is good, there wouldn't be an issue). Either way on the fan, it seems like cheap insurance to keep it running cool enough, so I'll go ahead and get that done. 

BTW, any idea of a good heatsink (no idea how hot it gets to select a decent sink), and should I use thermal epoxy or is the thermal tape sufficient in this case?

TIA. 

Never actually bought anything from a HAMB, so I've never run into that experience (great resources for information though). Never checked out liquidation sales as I never knew where to look, and assumed I'd have to buy lots rather than single pieces (even expected something like this to be closed to the general public without a membership of some sort).

[T4P]

I think if you just look at the size and check up farnell/newark/element14 or just aavid thermalloy you can get roughly what you want
Looking at the heatsink on google it looks pretty much like the heatsinks they used for the intel pentium MMX only less dense
I think you can get the ones meant for southbridges/northbridges if it can fit
And if you want a reliable silent fan get a Sanyo San Ace Silent series or a Delta AFB series

[nanofrog]

I think if you just look at the size and check up farnell/newark/element14 or just aavid thermalloy you can get roughly what you want
Looking at the heatsink on google it looks pretty much like the heatsinks they used for the intel pentium MMX only less dense
I think you can get the ones meant for southbridges/northbridges if it can fit
And if you want a reliable silent fan get a Sanyo San Ace Silent series or a Delta AFB series

Thanks for the reply. 

Don't have the scope yet, so I've not had the chance to actually see anything other than a photo of the U800.

Pic of a U800. http://www.qservice.tv/N_PICS/PICS_TEK_SPARES/ALL_9F/EX_LARGE/DSC09382.JPG
Pic of it mounted on the board. http://www.iowa-industrial.com/Western-Iowa-/Metalworking-and-Production-/Numberically-Controlled-Equipmnent-/Tektronix-2465B-U800-horizontal-amplifier-155-0241-02.cfm

[BravoV]

Don't have the scope yet, so I've not had the chance to actually see anything other than a photo of the U800.

Here in this forum, made a teardown thread on my 2465B which is quite identical to 2445B -> here

[nanofrog]

Don't have the scope yet, so I've not had the chance to actually see anything other than a photo of the U800.

Here in this forum, made a teardown thread on my 2465B which is quite identical to 2445B -> here

Thanks, this helps a lot.  BTW, I'll probably borrow your heatsink idea (looks really nice). 

[Rick]

Don't have the scope yet, so I've not had the chance to actually see anything other than a photo of the U800.

Here in this forum, made a teardown thread on my 2465B which is quite identical to 2445B -> here

On that thread, why don't you shape your heatsink so that it extends up to the bolt because the bolt is in contact with the bottom metal of the IC: http://www.qservice.tv/N_PICS/PICS_TEK_SPARES/ALL_9F/EX_LARGE/DSC09382.JPG
It's better than cooling only the body of the IC through that black body isn't it?
And instead of the bolts you could insert some more metal to elevate the bottom metal to the top level of the black body so that it touches the heatsink...

[BravoV]

On that thread, why don't you shape your heatsink so that it extends up to the bolt because the bolt is in contact with the bottom metal of the IC: http://www.qservice.tv/N_PICS/PICS_TEK_SPARES/ALL_9F/EX_LARGE/DSC09382.JPG
It's better than cooling only the body of the IC through that black body isn't it?
And instead of the bolts you could insert some more metal to elevate the bottom metal to the top level of the black body so that it touches the heatsink...

Rick, thanks for the suggestion, yes, I'm aware of optimizing the heat path, totally agree on metal beats plastic when it comes to heat conduction.

Actually that is only temporary solution, I'm planning to desolder the whole U800 IC and put a custom cut copper to cool it directly from below and I already have an idea how to proceed next, yes, I have the photo how that U800 ic bottom looks like. Too bad its just I travel a lot, just don't have time and commitment to do a major big surgery on that big ass A1 board yet. 

Geezz.. this is becoming off topic from this original thread's subject, sorry Vincent  , and if you want to proceed this discussion on improving U800 cooling, I will be really glad if we could continue this interesting subject in that thread of mine, and I will post the photo of U800's bottom as well to get possibly better idea to cool it better.

[KJR]

Found this post while trying to resurrect a 34970A with "all segments showing on front panel" issues.  What you posted is/was incredibly useful, thanks much for the effort to document your work.

FYI anyone else going down this rabbit hole, the equiv part that's readily available (for those of us without nearby bins of parts for $1 each) is the Allegro System A6818; I found a couple of vendors with Min Order Quantity of 1 at $5 each + reasonable shipping + 2 weeks wait on Ebay. 

Regards,

Kurt

[PTR_1275]

Hi guys,

I have recently bought a 34970 and the front encoder is a bit intermittent. When it works it is picking up every second click. As this is my first 34970 I am not sure if this is normal or not.

I dissasembled and checked the encoder, it has been replaced at some point as the soldering hadn't been cleaned after being re-worked. I looked in the service manual and the part number is ECL0J-C24-SE002. The only reference that I can find on Bourns' site is that it has been replaced with a ROHS version with a L at the end of the part number.

The encoder that is currently in the unit is a ECW1J-B24-AC0024L
I haven't ever worked with encoders nor can I find a breakdown of what the part numbers actually mean, are any of you with more experience able to comment on your thoughts? Are they only meant to pick up every second click? Is there a way for me to test this encoder and get something legible out of the results? What is the difference between the Agilent listed part number and what you have used for your repairs?

Thanks in advance

-Chris

[GNU_Ninja]

This data sheet ought to help. http://www.farnell.com/datasheets/1695367.pdf

[PTR_1275]

Thank you,

That makes a lot more sense. I put the encoder on the scope just after posting just to see what I could see, I am getting signals on both pins with each detent.

From the data sheet I am making assumptions (If they follow a similar naming convention across their encoders) that the factory encoder doesn't have any detents. If this is the case the user wouldn't know that the unit is waiting for 2 signals from the encoder to increase or decrease, but because this has detents I can tell.

That is of course if the units didn't originally come with detended encoders.

Cheers
-Chris

[TiN]

Semi-rigid flatcable between mainboard and display module.

Just reminded me, had same problem before in 33120A, those cable connectors are nasty.

P.S. oops, necrothread... 

[SteveyG]

Hi free_electron,

I don't suppose you recall the part number for the encoder? I want to replace mine as it's playing up, but want to disassemble, repair and reassemble in one go...

[coldframe]

Thanks,  free_electron!
Now, one question.
Please take a look at the attached photo.
It's probably 34902A 16-Channel Multiplexer
I'm not sure what to do about it.
What's this do?

coldFrame.

[free_electron]

that is a structure to test the capacitive coupling between layers. there is one of these on every layer. the top two testpoints are top layer, the next are inner 1 and so on.

they used this to find out how much cross coupling there is  between signals.

[coldframe]

It come to me about Humidity Sensor 
BTW thanks for letting me know.

[PTR_1275]

that is a structure to test the capacitive coupling between layers. there is one of these on every layer. the top two testpoints are top layer, the next are inner 1 and so on.

they used this to find out how much cross coupling there is  between signals.

I had seen this on my cards, but not given much thought as to what it is or why it's there. Makes sense once it's explained. Thanks

[DoricLoon]

Hi free_electron,

I've just purchased a Keysight 34970a. Was listed as parts on ebay with error 625. Should be arriving in the next day or two. I have seen one thread where low battery voltage was being linked to this error? (I should be so lucky) Just wondered if you have had any dealings with this particular error?  Service manual tells me lack of communication between main processor and outguard processor. I'm hoping for faulty 5V earth reference supply, reset or opto isolator problems. If it is the outguard processor will I be able to obtain a replacement? or have I spent £140 on a door stop?

Thanks in advance
Jim