Test Equipment Anonymous (TEA) group therapy thread

[vk6zgo]

Yep, shrink tube was around in 1969.

We tried some very large shrink tube back then, to try to hold a cable form together but in those days such sizes were made from a different material to the smaller diameters.
The resultant form turned out to be too stiff to feed through the cable ducts, so we had to revert to lacing the form by hand.

Or it could have been the predecessor to heat-shrink which was a chemical shrinking process. The tubing came immersed in a special chemical and sealed in a can. When the tubing was removed from the can and exposed to air it would shrink down.

It is a product that is now long gone, which is probably a good thing. I expect it used 100% carcinogenic chemicals as was the norm back in those days.

Nope! It worked just like the stuff we use today.
We shrunk it with heat guns.
The big diameter stuff came in a roll & was made from a different material to today's version.
Our application didn't work out, but it was used successfully elsewhere.

The small stuff was around but it was far less common than the large heat shrink.

[AVGresponding]

Back then, rubber sleeving would have been more common. The grey nylon cable tie is also non-contemporary.
Also note the assorted TO-33 heatsinks, with one missing altogether.

[factory]

An all purpose amp has good arguments to be bought.
This one was 30 Euros.
After a first test it seems to work in general.

First look with a IR camera shows the transformer running at 50 C and I'm not sure if that's OK.

And I have a doubt that there has been someone tinkering already, because
- there are scratched writings,
- I'm not sure if there has been shrink tube in 1969,
- there are kind of make shift cooling fins.

The white lens on the power indicator & IEC inlet, were used from around 1970 onwards, give or take a bit for them to use up stocks of older case parts.
And the printed HP logo is found on late units, instead of plastic or engraved logo.

As well as the 1978 datecodes on the T03 part and at least one of the Kemet tantalums also indicate a later unit, I'm guessing it has a prefix code starting 09xx due to the very minor production changes.

David

[Neomys Sapiens]

Sometimes one can have a strike of luck without aquiring something: when I checked today, I discovered that I have one more P6245 active probe than I had registered previously!
 

[factory]

Back then, rubber sleeving would have been more common. The grey nylon cable tie is also non-contemporary.
Also note the assorted TO-33 heatsinks, with one missing altogether.

Now you mention it, it seems odd to have one cable tie, when the rest is laced in that HP 461A. 

Don't know about non-contemporary, as the YHP 4270A I acquired uses grey cable ties all over, the design change prefix is 952, next prefix used was 1017J according to the pdf manual (ex Helmut Singer Elektronik) available on the web.


All cable ties now hidden again, now I've found screws to attach the loose bottom cover, top cover is AWOL, annoyingly it's one of those extra long covers  , not something common like those used on HP 140/141 that appear as bits on ePay, PH163 inlet was replaced by a previous owner/user.


David

[AVGresponding]

Back then, rubber sleeving would have been more common. The grey nylon cable tie is also non-contemporary.
Also note the assorted TO-33 heatsinks, with one missing altogether.

Now you mention it, it seems odd to have one cable tie, when the rest is laced in that HP 461A. 

Don't know about non-contemporary, as the YHP 4270A I acquired uses grey cable ties all over, the design change prefix is 952, next prefix used was 1017J according to the pdf manual (ex Helmut Singer Elektronik) available on the web.


David

I'd consider it extremely unlikely that those cable ties are original, though they are an older design, and it's a very neat job, but I don't think butt-splice crimp wiring is a factory feature.

EDIT: I'd expect lacing on something like this, presumably a technique beyond the skills of whoever bodged the new cables in with the crimps.

[vk6zgo]

Back then, rubber sleeving would have been more common. The grey nylon cable tie is also non-contemporary.
Also note the assorted TO-33 heatsinks, with one missing altogether.

Now you mention it, it seems odd to have one cable tie, when the rest is laced in that HP 461A. 

Don't know about non-contemporary, as the YHP 4270A I acquired uses grey cable ties all over, the design change prefix is 952, next prefix used was 1017J according to the pdf manual (ex Helmut Singer Elektronik) available on the web.


David

I'd consider it extremely unlikely that those cable ties are original, though they are an older design, and it's a very neat job, but I don't think butt-splice crimp wiring is a factory feature.

EDIT: I'd expect lacing on something like this, presumably a technique beyond the skills of whoever bodged the new cables in with the crimps.

The instrument is old, it would be naive to assume it had not been subject to rework sometime in its service life.
If a Tech has to fix something, they will use whatever is available to get the device back into service.

Nobody in the late 1960s/early 1970s would have painstakingly re-laced a cable form inside an instrument, when cable ties were ready to hand.
Around that time, those of us that had to cable things sighed with relief that we didn't have to use waxed twine, plastic cabling "cord", or just 1mm plastic tubing to cable wiring anymore.

I don't believe in the "return it to showroom condition" philosophy-----the various repairs, modifications, etc., are an integral part of the instrument's history. (Unless, of course, they are a total "bodge".)

"Form, fit & function" & the foremost of these is function!

[Robert763]

I'm pretty certain those plastic cable ties are original. I've seen them in other HP gear of that era. Don't forget many wiring looms were made off the instrument in batches. There is no reason why one loom in an instrument might have been made with lacing earlier, or even in a different location to the other(s) or final assembly.

Robert.

[factory]

Back then, rubber sleeving would have been more common. The grey nylon cable tie is also non-contemporary.
Also note the assorted TO-33 heatsinks, with one missing altogether.

Now you mention it, it seems odd to have one cable tie, when the rest is laced in that HP 461A. 

Don't know about non-contemporary, as the YHP 4270A I acquired uses grey cable ties all over, the design change prefix is 952, next prefix used was 1017J according to the pdf manual (ex Helmut Singer Elektronik) available on the web.


David

I'd consider it extremely unlikely that those cable ties are original, though they are an older design, and it's a very neat job, but I don't think butt-splice crimp wiring is a factory feature.

EDIT: I'd expect lacing on something like this, presumably a technique beyond the skills of whoever bodged the new cables in with the crimps.

I've also seen those grey cable ties in other HP TE, looking closely they are branded Ty-Rap, which were invented in the late 50s by an employee of Thomas & Betts.

The crimp connections are factory, they are used for the screen connection of the various coax cables.
Here are some close up pictures, of some in a 524x series counter, they were used in lots of older HP TE.





David

[AVGresponding]

I've also seen those grey cable ties in other HP TE, looking closely they are branded Ty-Rap, which were invented in the late 50s by an employee of Thomas & Betts.

The crimp connections are factory, they are used for the screen connection of the various coax cables.
Here are some close up pictures, of some in a 524x series counter, they were used in lots of older HP TE.





David

1958, in fact. I get (mildly) cross when my colleagues refer to all cable ties as Ty-Raps; like calling all vacuum cleaners Hoovers.

Thanks for clearing that up. Bearing in mind, I'm not an RF guy, why all the different colours and sizes of coax in the unit?

[factory]

1958, in fact. I get (mildly) cross when my colleagues refer to all cable ties as Ty-Raps; like calling all vacuum cleaners Hoovers.

Thanks for clearing that up. Bearing in mind, I'm not an RF guy, why all the different colours and sizes of coax in the unit?

I get pissed off everytime I hear Cinch when it's not referring to a brand of connector, those outside the UK probably have no idea what I'm rambling on about.

Back to the 4270A;
They seem to be using them for power as well as signals, a four core screened cable goes to the on/off switch too.

For example the bunch of different colored coax cables at the bottom of the picture, are the secondary windings of the power transformer, the manual mentions both the coax color code and the crimp sleeve color. Also noticed a few very thin coax cables that don't have the crimp sleeves.

Some more pictures of another 4270A here (from Cubdriver); https://pmanning.smugmug.com/Electronics/HP-4270A-Automatic-Capacitance/i-HzfbK3K

David

[TERRA Operative]

No TE for me at the moment. I just bought a bottle of Fireball whiskey and a bottle of Zubrowka vodka though...

I am waiting on parts for the THS720 scopes, along with custom foam inserts for the soft carry bags to arrive, so machinations are machinating in the background.
And I am in the process of building a range calibrator for my 437B power meter too.


Until then, bottoms up!

[Specmaster]

Yay, I'm off to Mansfield in the morning to pick up my lovely new car and can finally say goodbye to this pile of Japanese crap I've been driving for the last 2 months while I did battle with the insurance companies over getting a more realistic payment for my poor old car was written off for me by some inconsiderate driver on the 3rd April 

[Robert763]

I have a road trip tomorrow too. First part is 90 miles taking the dog to the vet for possible dental surgery. Then a further 50 odd miles either with dog or while she has surgery to pick up some TE.
I did a BIN on a HP 8920A radio communications test set. Collection only It's broken. Allegedly just the PSU. The PSUs on these are a bit odd. They accept mains or DC input with multiple outputs using a single high frequency transformer for both inputs. I've fixed them before. Very little other information on the unit. Only photos of the front. It has a CDMA adaptor attached. No idea of other options. That's the bad news. The good news is that it was only £75. Unless it is completely trashed I can't loose.


Robert.

[Specmaster]

Wow, thats so spooky Robert, your trip adds up to to 140 miles, which I take it will be double that for the return journey, and my trip is going to be 145 miles each way unless I also combine it with a trip to RAF Conningsby for some Typhoon action and possible some BBMF action as well as they practise for the forth coming display season, in which case I'll be doing around 330 miles altogether.

Good luck with the HP 8920A and I hope that the surgery is a success for your dog.

[Robert763]

Road trip complete. Dog has several fewer teeth and bank balance proportionally fewer pounds 

8920A picked up. Looks good. Cal seals are intact so hasn't been robbed or messed with. It also has the high stability reference (050) and Spectrum Analyser / Tracking Generator (102) options. 

Less useful is 007 low power input (4W max) but not a huge problem an external attenuator sorts that. I may actually have the high power option in my stock of bits.
Next is extraction of the PSU and see what the damage is. Report is it was working OK and then went "pop" and emitted smoke.

Robert.

[Robert763]

So an hours dissasembly later... Did I say these things are a pain to work on? The failure mode is obvious. We have a blown RIFA 47nF. Unfortunatly this is not in a filter circuit it's a snubbber. The failure start a chain reaction so we have a blown main switch transistor. Literally bits blown off the encapsulation. Blown driver and two smoked resistors.
Now for some parts identification....

Robert.

[m k]

For the backplane,
I've many times wondered how speed and frequency vs. backplane style is sort of misguiding.
Like when bus terminators are needed and wires are carefully placed on PCB and then the wire wrapped backplane is sort of what ever.

[Robert763]

HP 8920A Radio test set PSU repair update.
On the mains side we have literally blown up IRF 840 main switch MOSFET, ZXT650 driver bipolar, 0.1R 1W, 4.7R 1/4W resistors and 47nF RIFA. Not obvious is 9.1V 1.3W zener short circuit. Replacing those got it running but output voltages ar a bit off and a couple of output electrolytics getting warm 
Most of the output electrolytics were starting to leak physically and electrically. So replaced all those too. Just having a cup of coffee before a final check and putting the PSU back together and plugging in...

Robert.

[Robert763]

So the 8920A PSU didn't work. The OVP crowbar is triggering. Now this is a issue because its hard to tell if the crowbar is faulty or the regulation loop. The unit is densly packed so hard to work on. And of course it's mains powered so can bite. These power supplies are unusal in that they use a transformer to isolate the feedback. It's T2 in the picture.

A small ferrite toriod with 3 windings. Two on the mains side, one on the low voltage side. One mains winding drive the gate of the MOSFET. Not totally clear how it works but looks like the LV side causes the core to saturate and terninate the drive to MOSFET. Anyway, one of the primary windings was open circuit. Hard to find in circuit because it is shunted by low value resistors.
Fortunately I was able to dig the fused end of the winding out and repair it.
PSU fixed 
[ Specified attachment is not available ]
Don't worry about the failure message, the input module isn't connected. I was not going to put it all back together for a PSU test. Not putting it back together tonight. It's been a long day and I don't want to malke a mistake.

Robert.

[tautech]

Anyway, one of the primary windings was open circuit.

Had the glue corroded the winding ?

[factory]

HP 8920A Radio test set PSU repair update.
On the mains side we have literally blown up IRF 840 main switch MOSFET, ZXT650 driver bipolar, 0.1R 1W, 4.7R 1/4W resistors and 47nF RIFA. Not obvious is 9.1V 1.3W zener short circuit. Replacing those got it running but output voltages ar a bit off and a couple of output electrolytics getting warm 
Most of the output electrolytics were starting to leak physically and electrically. So replaced all those too. Just having a cup of coffee before a final check and putting the PSU back together and plugging in...

Robert.

Having read your repair, I'm glad I replaced the RIFA madness snubber cap, in the HP 54615B* scope when I acquired it, seems to also use a Computer Products PSU, but not the same one.

Are you going to name & shame the peeing capacitors?

*Seems Scottrade has a basket case 54615B, described as missing the power socket, nope missing the whole PSU more like.    eBay auction: #325678748332

David

[Robert763]

Anyway, one of the primary windings was open circuit.

Had the glue corroded the winding ?

No. When the MOSFET when short due to the snubber failure the main (300V DC) filter capacitor discharge path included the winding and it fused.

[Robert763]

HP 8920A Radio test set PSU repair update.
On the mains side we have literally blown up IRF 840 main switch MOSFET, ZXT650 driver bipolar, 0.1R 1W, 4.7R 1/4W resistors and 47nF RIFA. Not obvious is 9.1V 1.3W zener short circuit. Replacing those got it running but output voltages ar a bit off and a couple of output electrolytics getting warm 
Most of the output electrolytics were starting to leak physically and electrically. So replaced all those too. Just having a cup of coffee before a final check and putting the PSU back together and plugging in...

Robert.

Having read your repair, I'm glad I replaced the RIFA madness snubber cap, in the HP 54615B* scope when I acquired it, seems to also use a Computer Products PSU, but not the same one.

Are you going to name & shame the peeing capacitors?

*Seems Scottrade has a basket case 54615B, described as missing the power socket, nope missing the whole PSU more like.    eBay auction: #325678748332

David

The Failed parts. Not much left of the ZTX650. he fuse just did it's job.
[ Specified attachment is not available ]

[factory]

HP 8920A Radio test set PSU repair update.
On the mains side we have literally blown up IRF 840 main switch MOSFET, ZXT650 driver bipolar, 0.1R 1W, 4.7R 1/4W resistors and 47nF RIFA. Not obvious is 9.1V 1.3W zener short circuit. Replacing those got it running but output voltages ar a bit off and a couple of output electrolytics getting warm 
Most of the output electrolytics were starting to leak physically and electrically. So replaced all those too. Just having a cup of coffee before a final check and putting the PSU back together and plugging in...

Robert.

Having read your repair, I'm glad I replaced the RIFA madness snubber cap, in the HP 54615B* scope when I acquired it, seems to also use a Computer Products PSU, but not the same one.

Are you going to name & shame the peeing capacitors?

*Seems Scottrade has a basket case 54615B, described as missing the power socket, nope missing the whole PSU more like.    eBay auction: #325678748332

David

The Failed parts. Not much left of the ZTX650. he fuse just did it's job.
(Attachment Link)

Thanks, will have to take a closer look at the PSU next time I work on it, seems to mostly have Nippon Chemi Con LXF, with some Rubycon, but lots of glue hiding the details.



David