Test Equipment Anonymous (TEA) group therapy thread

[rdenney]

I'm not exactly sure why I bought it, except that I needed a better signal generator, but I have an HP 8904A arriving today....

The 8904A arrived, after several days of battling with Fedex on making the delivery. I have a long gravel driveway, and I set my snowblower high enough to blow snow and not gravel, so there's still an inch or so of white over the gravel that has now frozen in place. UPS USPS, and Amazon have had no trouble driving back to the house, and my wife and I both drive on it every day, but Fedex reported the driveway impassable and refused to make the delivery. Because it was an ebay purchase, they were initially unwilling to allow it to be rerouted to a pickup location, but eventually they accepted that request and I was able to fetch it yesterday.

I went through it last night, though I have not yet taken the covers off of it. It's a plain 8904A--the sticker on the back says Option 006 (which is the 600-ohm transformer-loaded balanced output)--but no Option 001 or 002. I knew I wasn't getting the second output, but I did want all four synthesizers that could be used to feed the main output. The memory hack trick worked perfectly to enable Options 001, 003, and 005. Testing it with summing four frequencies onto the output works perfectly, and I think the unit is working fine.

As is usually the case, the flourescent backlight is very weak, and the display has one missing horizontal line in the upper row of characters. I have ordered a 2x40 LED-backlit display to make the conversion.

Next step is to pull the covers and check the battery, and investigate the FM modulation function to see if I have the newer feature.

Rick "only had a few minutes and forgot to check the serial number" Denney

[factory]

I had no luck repairing these knobs, for the reason stated above that they shrank and the metal core caused them to split.

Furthermore, removing the metal core is no mean feat. The set screws on my 339A were so tight that I couldn't make any headway using the good-quality .050 hex key that would fit them. Once they stripped, I was done. I ended up using a very small diamond burr on a Fordham tool to cut a slot in the metal collar to get it off the shaft. Then, I scrounged on ebay for replacement knobs (long-term patience required). These are expensively made knobs, but they probably couldn't have predicted shrinkage after 3-5 decades.

Rick "thought he might have to machine new knobs from scratch" Denney

I've had good success removing HP knobs by tightening the screw slighty, to crack the threads loose, then they undo much easier.
The Tek ones with a aluminium insert are a PITA, they are almost impossible to remove once rusty/corroded.

I second Dichloromethane. Sold to modellers in the UK as EMA plastic weld.
https://www.amazon.co.uk/Plastic-Cement-Stick-Plastics-Weald/dp/B00QQNNWIW
Works perfectly for these knobs. Apply to the inside (under skirt or top cap) I use a short length of tiny ptfe tube used to insulat component leads. Capillary action will draw the solvent into the crack.

Interestingly Dichloromethane is very hard to get in the UK other than this. It was banned from it's main use, paint stripping.

Robert.

I'm not surprised it's hard to obtain, I read something in the news earlier about a bathroom fitter, using DCM based glue for flooring in a confined space, they died from the fumes after a spray can of the stuff got damaged.

David

[McBryce]

What is the best way to repair a HP knob like this?


https://www.miedema.dyndns.org/co/2025/IMG_4757_Broken_HP_knob-2000pix.jpg

I tried before using epoxy glue (Bison Combi snel/rapide). But that did not work too well. So I am curious what you are using...


This particular knob belongs to a HP 5300A + 5303A counter, made in 1971.
The counter came in my possession with an IC missing. At that time there was no service manual available.


https://www.miedema.dyndns.org/fmpics/Circuits_online/HP5303A/IMG_3565__HP_5303A_missing_IC-2000pix.jpg

This resulted in a nice topic: HP 5303A counter is missing unknown IC... with a lot of (tear down) photos. With some detective work the correct part number was found. A bit later, Dave of Artec found a 5303A manual, and scanned it for me. It confirmed that the found part number was correct.

But now I have to glue the knobs again....

regards, Gertjan.

I've had a similar issue in the past. Can't remember exactly which device it was, but as mentioned above, the plastic had shrunk too much to ever join up again and whatever that plastic is (very hard, brittle, almost like bakelite), it wouldn't stick no matter what I tried. This is definitely a situation where 3Dprinting a new one is really the only solution unless you can find an original spare.

McBryce.

[Gertjan]

What is the best way to repair a HP knob like this?

Thank you all for sharing your experiences!

The Dichloromethane gets the most votes. I ordered a bottle EMA plastic weld.
It seems the best solution to weld the plastic together. But it needs good fitting surfaces, and will not attach to the brass core (for extra strength).

In the past I had bad experiences with super-glue. But maybe I didn't use it right, and it seems that there has been a lot of development in super-glues.
Advantage is that it will also work if the crack is not super clean, and it also glues the plastic to the brass core. I also ordered the Loctite 401 superglue.


I removed the knob from the counter, to have a good look with my stereo microscope. (For a change, it was easy to loosen the grub screws with a good fitting Allan key )

This is the crack I originally glued with epoxy glue (maybe 10 years ago) :


IMG_4763__HP_knob_old_crack_outside-2000pix.jpg

The epoxy just did not attach very well to the plastic. This make me think that this plastic is ABS, as it is known that epoxy does not work very well with ABS.

But I also noticed e few new cracks. The largest can be seen in the background

The same old crack from the inside:


IMG_4759__HP_knob_old_crack_inside-2000pix.jpg

When I originally tried to glue with epoxy, I also tried to glue the plastic to the brass core. But this also came loose...

The biggest of the new cracks:


IMG_4761__HP_knob_new_crack_inside-2000pix.jpg

The new cracks are very clean. so I think these are good candidates to glue with the Dichloromethane.

But I doubt if I can get the old crack cleaned op enough, with both surfaces fitting perfectly for using the Dichloromethane.
So I will try to glue that with the super glue.

Sounds like a complicated approach, but I hope to improve my skills a bit in this department

regards & thanks, Gertjan.

[squadchannel]

Pull out the brass core inside, fill the syringe fully with dichloromethane, inject it, then secure the knob with masking tape. That should do the trick.
One drop is enough to penetrate. the key is to fill the syringe completely because it's highly volatile. Otherwise, the heat from your hand will cause the liquid to evaporate and ruin everything.

problem is whether you can put the pulled-out brass core back in. it might be break.

[TERRA Operative]

I might run down to my local Viva Home or Joyful Honda to grab some of that stuff.

[Black Phoenix]

Well, the family increases:

- Fluke 289;
- Fluke 87V;
- Fluke 107;

And today the Fluke 787 was added to the collection. A NOS unit, for way less than I was expecting: 1500HKD.

[Gertjan]

Pull out the brass core inside, fill the syringe fully with dichloromethane, inject it, then secure the knob with masking tape. That should do the trick.
One drop is enough to penetrate. the key is to fill the syringe completely because it's highly volatile. Otherwise, the heat from your hand will cause the liquid to evaporate and ruin everything.

problem is whether you can put the pulled-out brass core back in. it might be break.

Thanks for the tips!

I tried, and with a bit of pushing, I can easily close the gaps of the cracks. (with the brass insert still inside)
So I will try gluing with the brass core in place, and then clamping the knob in something like a drill-press. (Using the method described by Robert763)

regards, Gertjan.

[squadchannel]

I forgot to mention. if it splashes, it'll be a real mess. all melt. I messed up once and left a mark on the 5335A screen.
it's prone to splashing until the syringe is completely full. Be careful.
If it gets on your hands, it's no big deal. It feels a bit cool, but it evaporates in less than a second. (99.9% dichloromethane)

[Gertjan]

Thanks again squadchannel.

It will be some time before I get round to gluing the knob. I had to order the EMA plastic weld from the UK, with an estimated delivery date between the 20th and 25th of February. Dichloromethane is nowhere to be found in The Netherlands these days...

regards, Gertjan.

[rdenney]

8904A report:

This is not the same unit the seller pictured, which is a good thing. 1.) It came with feet, including the tilt stands, which weren’t shown in the pictures. 2.) It’s much newer: the serial number is 3633Axxxx, indicating a 1996 production date. This fits the date codes on the IC’s. The pictured unit was ten years older. 3.) The battery is the newer (and readily available) Panasonic BR-2/3A, with a date code that is probably 1995 (the code shows the year but not the decade). The battery measures 3.32 V, and the data sheet shows that all voltages at 50% discharge should be below 3 V—I don’t think I’m going to stress about it for now. 4.) The FM tuner feature is available now that I have option 001 enabled.

It’s an Option 6 unit (also not consistent with the sale pics but fine with me for audio use), and the 600-ohm output transformer is installed. I believe from the instructions that this only applies when using the differential output, and it’s still 50-ohm when just using the single-ended high referenced to the shield. The output voltage is adjusted to reflect the expectation of loading, I gather, and displays 1 volt when a scope, DVM, or other hi-Z device measures 2. A 600-ohm through terminator corrects that.

Accuracy: 1000 Hz programmed reads 999.9992 Hz on my OCXO 5334b, and .99999 KHz on the 8903b distortion analyzer. Which, by the way, reports a SINAD of 78 dB, bang on spec for the standard model, slightly better than spec for the Option 006 model. 1.000 V displayed output reads 2.003 V on hi-Z devices.

The only flaw is a missing pixel row on the upper display line, but I have a replacement display on the way.

Rick “lucky again” Denney

[Mr. Scram]

In the past I had bad experiences with super-glue. But maybe I didn't use it right, and it seems that there has been a lot of development in super-glues.
Advantage is that it will also work if the crack is not super clean, and it also glues the plastic to the brass core. I also ordered the Loctite 401 superglue.

Superglue is amazing stuff in the right application, but it often gets used in places it struggles. When gluing plastics, there often are other, much better solutions. If you can find a substance that chemically welds your plastic, that's usually the best option. If there are gaps to fill, you can sometimes make a slurry with excess bits of the plastic and/or an additional small particle filler.

Though I second the suggestion to look into a printed replacement. Even if you manage to stick this knob together, it seems it would be a compromised solution.

[zepto]

Found this at the local electronics surplus store. I'm not really a Tektronix fanatic, but I do love bridges and this thing was way too cool looking. The test equipment at the store is usually really expensive, but sometimes niche items can be had for a decent price. I tried testing it and it did not seem to be functional, but then I found this page https://w140.com/tekwiki/wiki/067-0543-99 where they say the error signal is AC (for a DC voltage bridge?!)

[Robert763]

The output is AC because the design uses a chopper to turn the input to AC.

[Gertjan]

What is the best way to repair a HP knob like this?


https://www.miedema.dyndns.org/co/2025/IMG_4757_Broken_HP_knob-2000pix.jpg

I tried before using epoxy glue (Bison Combi snel/rapide). But that did not work too well. So I am curious what you are using...

Today I glued this knob.
It had an old crack that I had previously tried to glue with epoxy, and a fresh crack.

When I tried to remove the old epoxy, the knob broke into two halves:


IMG_4786__HP_knob_broken_into_2_halves-2000pix.jpg

This was actually a good thing, because it was now much easier to scrape the old epoxy glue off.
I was surprised how bad the bonding of the epoxy with the plastic of the knob was. Epoxy and ABS is certainly not a good combination. (Or maybe I did not clean the surfaces well enough before glueing?)

After scraping away as much epoxy as I could, the surfaces of this old crack were still not perfectly matching. so I decided to glue this crack wit the Loctite 401 superglue:


HP_knob_glued_with_Locktite_401-2000pix.jpg

I used just a tiny bit of glue to avoid spilling it over the outside of the knob, and that worked out very well.  Also, I was afraid that the superglue would harden before I got the parts in position, but this was no problem at all.  I let the glue dry for 2 minutes while I pressed the two halves together with my fingers, and then clamped the knob as in the photo.


The other (new) crack had very clean, well fitting surfaces. So I decided to try the EMA plastic weld (Dichloromethane).
I did not have a glass syringe, and was afraid a plastic one would be dissolved by the glue. So I followed the tips of Robert763, and used a a short length of tiny PTFE tube.
I think the idea is  to fill the tube with Dichloromethane, put your finger on top of the tube, and let it go when in position near the crack.
This worked, but the tube also functioned as just a stick, when dipped into a liquid, some drops will stick to it. 

What ever, it worked fabulously:


IMG_4788__HP_knob_glued_with_EMA_plastic_weld-2000pix.jpg

With the knob clamped as in the photo, I applied a few drops on the inside of the crack. The water-thin fluid wicked between the plastic and the brass, and into the crack. Like magic, and very easy to do.
For good measure, I turned the knob over, and also applied a few drops into the other side of the crack.

This EMA plastic weld is really nice stuff!
It is not as highly volatile squadchannel warned me for. I had the time to carefully put the drops in the right place, without evaporating in front of my eyes. But then this is not pure Dichloromethane, it is plastic weld containing Dichloromethane. So I suppose the stuff is optimised for the job in hand.


The result, the cleaned and glued knob:


IMG_4791__HP_knob_glued_with_EMA_plastic_weld-2000pix.jpg

This is the crack, glued with the Dichloromethane. With the naked eye it is nearly invisible.
The crack glued with the Locktite 401 it a bit more visible, because the less good matching surfaces. Still, with the naked eye hardly visible.

I am happy . And I learned a bit more about gluing plastic. I will use both glues more often. So thank you all!!

regards, Gertjan.

[Addicted2AnalogTek]

I have a questionable habit of scoring nice deals on things I do not need more of and not investing into the things that my bench would greatly benefit from. With that said, I couldn't resist and arrived home today to unload a stack of goodies which I promptly stuffed under the workbench before the wife got home. Among said TEAS City goodies are:

-HP 4145B with fixture & triax, but missing the disk.
-Keithley 619 Electrometer/Multimeter 2x6194 & 6193 Modules
-Deuterium Lamp Power Supply
-Lakeshore 330 Temperature Controller
-EG&G 1201 Lockin Amplifier
-Ol' Crusty HP 8405A Vector Voltmeter
-Tekprobe 1103
-Cute little HP 6217A Power Supply
-Tektronix CSA803A, SD-24, SD-42 with only 92 powerups and 66.8 hours

I did it all for the SD-24 module, and I'm not ashamed.

[TERRA Operative]

The 4145B responds well to a hxc slim floppy disk emulator.
https://lotharek.pl/productdetail.php?id=38

I am building a carrier kit for my 4145A and 4145B that will consist of a mounting board and a 3D printed blanking panel for the hole in the front panel.

[Addicted2AnalogTek]

Nice! I'll check into that emulator. I also need to find some of the test fixture jumpers, as I only have two pin to grabber cables for it. I did do a quick search and found replacement 3.5" floppy disk purchase options (slim to none), the USB floppy emulator fix, as well as a quick mention on a document I've since lost that read "....unlike the 4145B which can write it's own program disk". I assume that just means you can use the 4145B itself to write backup disks once it has booted up off of the currently available copy, because that would just be way too convenient.

[wkb]

Gertjan, PB to you failed. I might have a knib for you here, depends on the diameter it needs to fit on.

Wilko

[TERRA Operative]

Nice! I'll check into that emulator. I also need to find some of the test fixture jumpers, as I only have two pin to grabber cables for it. I did do a quick search and found replacement 3.5" floppy disk purchase options (slim to none), the USB floppy emulator fix, as well as a quick mention on a document I've since lost that read "....unlike the 4145B which can write it's own program disk". I assume that just means you can use the 4145B itself to write backup disks once it has booted up off of the currently available copy, because that would just be way too convenient.

I have a spare working boot disk, and if I get the floppy drive working again I can make some copies for you (I also have new-old-stock DD disks).
Let me tinker a bit, see what I can dig up.
Or if you can wait, I'll have some spare parts for the floppy emulator mod once I get it finished. Gotta buy a minimum of 5 PCB's (that I'm using to mount the HxC floppy emulator into the instrument) so I'll have a few spare.

I also figured out the parts to make new jumpers, and made a batch, I'll dig out those notes and give you part numbers. IIRC, I bought the plugs from RS Components.

Pull out the brass core inside, fill the syringe fully with dichloromethane, inject it, then secure the knob with masking tape. That should do the trick.
One drop is enough to penetrate. the key is to fill the syringe completely because it's highly volatile. Otherwise, the heat from your hand will cause the liquid to evaporate and ruin everything.

problem is whether you can put the pulled-out brass core back in. it might be break.

(Attachment Link)

I just bought some of this today, the exact same bottle from my local home center.

It worked brilliantly to repair the broken screw standoffs in a HP 3468A.
I officially really like this stuff and I think I'll use it much more often for repairing cracked plastics instead of superglue from now on.

[Gertjan]

Gertjan, PB to you failed. I might have a knib for you here, depends on the diameter it needs to fit on.

Thank you for the offer Wilco!  But I am good:


IMG_4803__HP_5303A_knobs_repaired-2000pix.jpg

I found some more opportunities to practice gluing with the EMA plastic weld.
When looking at the other knobs with my stereo microscope, I noticed more cracks around the top of the knobs.

Now I used a bit wider piece of PTFE tube. And indeed is was very easy to dip this in the bottle, close the top of the tube with a finger, and thus pickup a bit of fluid in the tube. Release the finger when the tube is in right position for the glue, et voila...

Also, now I glued in 2 stages. First drip a little bit of glue on the crack. It will seep into the crack. When dry, apply a bigger drop of glue over the crack. The top surface will melt, and after drying the crack will be invisible.

So, as usual, practice makes perfect.

In retro-respect, I think that the new caps on the knobs were the cause of the cracks. Although they were the right size (for 10mm inner diameter), they pushed a bit to much the old plastic apart. I cut a bit from the edges of the caps, and now all is fine.

(When I got this counter, not only an IC was missing, but also a knob and all knob caps. I decided not to try to make the counter original, but went for for a new look, using parts that were obtainable. Knobs for 1/4" and 1/8" shafts are not easy to find in The Netherlands...)

regards, Gertjan.

[TERRA Operative]

I like those dot matrix displays.

[Addicted2AnalogTek]

I have a spare working boot disk, and if I get the floppy drive working again I can make some copies for you (I also have new-old-stock DD disks).
Let me tinker a bit, see what I can dig up.
Or if you can wait, I'll have some spare parts for the floppy emulator mod once I get it finished. Gotta buy a minimum of 5 PCB's (that I'm using to mount the HxC floppy emulator into the instrument) so I'll have a few spare.

I also figured out the parts to make new jumpers, and made a batch, I'll dig out those notes and give you part numbers. IIRC, I bought the plugs from RS Components.

That'd all be greatly appreciated!
In an ideal world, I'd get my hands on a cheap copy of the boot disk to make sure all is well first and then invest into the emulator. However, I'll just have to work with whatever comes first and assume that this machine will be fully operational again. Considering its current condition and where it came from, I expect it has low hours and will be functional.

Count me in for one of those PCB's and whatever else you're able to provide for the kit (I don't own a 3d printer just yet....). Of course, I'm happy to pay you for it.

[TERRA Operative]

I have spare 3D printed blanking plates.

I'll work on the disk first as that's the easiest thing to start with, and it'll get my instrument open to finish the conversion kit too.

[Vince]

I have a questionable habit of scoring nice deals on things I do not need more of and not investing into the things that my bench would greatly benefit from.

Oh yeah I know that problem too well !! 

This realisation allowed me to heal from my TE accumulation illness.

I decided that stacking 45+ scopes, makes little sense when at the same time I don't even have space or money to buy very basic tools and supplies to equip my lab.
So in the past year I used that reasoning as a motivation to help me find the mental strength required to get rid of some TE, in exchange for new tools that actually add new capabilities to the lab.

So, I have managed to reduce my scope collection from 45+ down to (I just counted them) "only" 38. I am hoping by the end of the year I can get that down to 32, a nice round number, well, in terms of powers of two that is.

This strategy is now starting to pay : I just treated myself with a new toy for the lab, a desoldering iron, to help me make even more space, by getting rid of my 5 large plastic boxes full of scrap boards. I already junked 3 of them. I kept only the boards that carry some components I care enough to salvage, general purpose stuff that actually might stand a chance of actually being used in my life time. Maybe.

I spent a few hours playing with it on a large 4 layer (I think) old digital board, where every single component has all of its pins soldered on both sides of the board, freaking hell. A perfect testing ground I thought.

It's a motherboard from an old GOULD 1604 scope. At first I was very disappointed by that iron, thought it was achieving nothing and was a waste of money, a scam... but after some practice and fine tuning my technique, it actually delivered results which, though not magical, are well worth the investment. So no regrets. One more useful tool added to the lab.  One big motivator for buying this thing was that processing tons of old boards for components, is EXTREMELY expensive in terms of flux and solder wick, these things cost a fortune. The desoldering gun allows to drastically reduce my needs of flux and braid, in the long term. I now reserve them for jobs where they actually are the best option, whereas before the desoldering gun, I had to waste lots of those precious supplies because it's all I had to do the job.