Hi all,

I recently picked up a HP 8648C Sig Gen and am trying to figure out exactly what it is...
It had the serial and option stickers removed (A semi-common thing here in Japan when companies liquidate old gear, because reasons) so I'm trying to figure out just what this unit is fitted out with.
Luckily the instrument stores the serial number in its memory, so I was able to use GPIB to read it out: 3426A00711

The three plug-in modules inside are a little strange when checking their part numbers... The part numbers don't seem to exist in the service manuals I have found, but they do exist when checking the Keysight Parts Finder website.

Details as follows:

A4: 'OPT REFERENCE' P/N: 08647-61046 ->?Described in Keysight Parts Finder as 'Replaced by 08648-60042', which is 'MOD Assembly REF - 1E5' so I guess I scored the option 1E5, high stability time base.

A5: 'SIG GEN SYNTH' P/N: 08647-61050 -> Described in Keysight Parts Finder as as 'RF Synthe Assembly For 8648B' (I assume the B designation isn't exclusive to the B model as there are many parts shared between B, C, and D models?)

A6: 'RF OUTPUT' P/N: 08648-60116 -> Described in Keysight Parts Finder as as 'MOD AY-OUTPUT'.


Does anyone know why these part numbers are different to the manuals (Both Agilent and HP branded manuals)? Maybe I have an older unit and they are just older part numbers?
Also, does anyone know what 'Mod AY' is?


Thanks!
Jared

I only have a guess, but the one output-related option I'm aware of is for higher power (20dBm, if memory serves). Perhaps that's what "MOD AY" is. Try setting the output power to around that value and see if the instrument accepts it.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

I'll have to wait until I reassemble the instrument to try...
I'm currently dealing with a fresh-popped Rifa capacitor (the first Rifa that popped on my bench! So exciting, and stinky... :D ) and a few other repairs here and there.
Shouldn't take much longer than Mouser takes to deliver a couple parts.

If anyone happens to have a scanned copy of the earlier service manual they can upload, or can scan their paper copy, that might reveal some info. Manual part number 08648-90001


Thanks,
Jared

On 11/29/23 20:40, Jared Cabot via groups.io wrote:

I'm currently dealing with a fresh-popped Rifa capacitor (the first Rifa that popped on my bench! So exciting, and stinky... :D ) and a few other repairs here and there.

Mmmmm, love that Rifa smell. NOT. ;)

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

Hmm. 240VAC mains? I'm aware of this problem but never experienced it. (Thank the magic smoke gods!) When I would check, they all used the sealed EMI filter modules. Fingers crossed!

A lot of the HP gear will report (via HP-IB) the installed options. I did NOT see that command in the User Manual but it might be there. Something like OP? or similar.

Step One: GET IT WORKING!
Step Two: Don't worry about it that much. You will figure it out.

Cheers!

On Thu, Nov 30, 2023 at 11:21 AM, Mark Bielman wrote:

Hmm. 240VAC mains? I'm aware of this problem but never experienced it. (Thank the magic smoke gods!) When I would check, they all used the sealed EMI filter modules. Fingers crossed!

A lot of the HP gear will report (via HP-IB) the installed options. I did NOT see that command in the User Manual but it might be there. Something like OP? or similar.

Step One: GET IT WORKING!
Step Two: Don't worry about it that much. You will figure it out.

Cheers!

This Rifa popped on only 100V (Japan)! So it must have really been in a bad way.....
Once I get a new backup battery from Akihabara tomorrow, and a new contrast pot from Mouser next week, I'll have it all back together again.
It was running until the Rifa madness, so it should be all good to go again if I don't break anything else in the mean time.



On Thu, Nov 30, 2023 at 01:19 PM, Tom Haynes wrote:

Hi Jared,

?

You will need to do a little choose-your-own-adventure hunt through the manual.

?

Your device is 3426A.

?

The manual on keysight's site is for 4037A/U and doesn't contain errata or a back dating reference.

?

XDEVs has a manual for 3847A/U. It mentions your known replacements but not originals. It also doesn't have back dating.

?

Rensselaer Polytechnic Institute Has a manual for 3816A. Newer part numbers and no back dating.

?

And that is the oldest I can find. Your unit is 4 years older. Those modules have a lot of changes over a short time so it makes sense yours are earlier. For the most part these revisions are minor schematic changes. Sometimes reducing part numbers, replacing out of production parts, safety or stability fixes. The newer schematic are probably fairly close to originals.

?

You can check out my 8662A notes for an idea on how assembly history works.

Thanks for the info! The only manuals I have found around the place for my serial number so far are paper ones on ebay that will cost me US$60 to get into my hands.
Not too much really, but a download is free... :D I'll just have to justify it to myself for a few minutes before I can hit that buy button. haha. If I do buy one, It'll be scanned and uploaded for others to use too.





Also, if anyone has a rear foot/handle or two (P/N 08647-40003) and a front panel (I just need the frame not the buttons and display etc) they can sell, I'm interested.
I drew up the rear foot handle in CAD, so I can get some machined in China from aluminium and anodized for a half decent price anyway.




Jared

Here are some photos I took of the inside of my unit. Maybe these will help. The pulse option (1E6) is the gold block next to the reverse power protection unit. The modulation option (1E2) is a board mounted underneath the RPP/Pulse sub-chassis. I can’t find a description of where the high power option (1EA) is from the manual but I assume maybe it’s integral to the A10 board? The manual doesn’t have anything that jumps out at me about it, though I’ve only given it a cursory overview.?

The B/C/D units have the A10 frequency extension board which is on the far side of the card cage and encased in a cast aluminum housing (the first photo showing the barcode). I don’t think the A10 is used for the A models.

Thanks for the photos!

I can confirm that I do not have options 1E2 or 1E6 as the parts don't exist in my unit. They aren't options I need anyway so no problems there.

The 1EA high power option is intriguing me though. With no reference to special parts in the 'Replaceable Parts' section of the service manuals I have found online, I'm wondering how a repair technician is to ensure that the option still works if the mysterious critical part is inadvertently replaced? How to ensure the part is not replaced with a non option part if there is no differentiation in the manual?

Which has me thinking further, is it just a software option? Maybe it changes the gain settings on the amplifier or attenuator settings to allow more upper range?

I wonder if just using the adjustment software etc to tell the instrument that it has the option installed will enable it?

Worth digging deeper I think, that high power option is a useful one...



Jared.

Hello Jared,

I don't know if someone has suggested this already, but did you check the 8920A CLIP??? It has some similarities to modules in the 8648. See:



Tom

Thanks for the info. :)


I ended up buying an earlier manual to suit my serial number (Which doesn't seem to be available online), so one it arrives I'll scan it in and upload it here and there.
Maybe it'll have some info that I seek...


Jared

And I got a little carried away again...

I drew up the rear handle/foot (08647-40003) to replace the missing part on mine and uploaded the file to thingiverse in case someone else needs one.


And also drew up the front frame too which I'll get made in aluminium in China if I can't find a replacement from a scrapped instrument for a decent price.
I'm 99% confident that it will fit perfectly, but that means it probably won't first time and will need a tweak. :D







Jared

On 12/3/23 11:16, Jared Cabot via groups.io wrote:

And also drew up the front frame too which I'll get made in aluminium in China if

Wow! Are you for hire if I need an electronics enclosure designed? Which CAD do you use? I've done some with FreeCAD...
--
John Griessen -- building lab gear for biologists
Albuquerque NM blog.kitmatic.com

Ha ha, I've been using Rhinoceros 3D for about 20 years now. I'd consider myself 'ok-ish' at it. Just hobby use but I can usually get done what I need with it.

I might be open to helping design some small stuff. I already do a little electronics product design work on the side, so I'm sure I can handle a little bit more here and there.



Jared

开云体育

Hmm, that front panel model is impressive! Perhaps I should revisit Rhino, I looked at it many years ago (>14) but just couldn't seem to get my head around using it as a 'parametric' 3D CAD, somehow I couldn't engage with the process/workflow back then. Anyway 'someone else' was paying for my SolidWorks dongle back then too!

Like John, I've been using FreeCAD a lot for the last 2-3 years and it is pretty capable *but* for the well known 'TNP' or Topological Naming Problem' issue which causes models and assemblies to self destruct before your very eyes, seemingly at random at first, while not insurmountable it drives most people - me included - totally nuts and can double or triple the time taken to develop both individual models and assemblies, especially when one is in the iterative stages of developing a new product!

For producing a model of a totally defined part such as that panel, TNP is not really a problem once you (finally!) get to grips with how to avoid it biting you.

There is hope however, a solution to TNP based (I think?) on the 'RealThunder' branch of FreeCAD is being actively incorporated in the main release but I believe it's still a little way off.

I have only briefly dabbled in FreeCAD a few years ago, but barely even used it. My muscle memory in Rhino is too strong. :D


As for the front panel, it looks like the part is rather expensive to get made even in China due to its size..


So, if anyone has a front panel to suit the LCD type display, I'm interested! I don't actually need the dials, LCD, PCB, Buttons etc so you can keep them for your own spare parts, I just need the aluminium frame itself.
I think any of B/C/D models will be fine. (A version has different text on the output jack), as long as it's from the LCD display version as the window in the mylar overlay is a different size.