Oscillo-Clock - 3BP1 CRT problem [SOLVED]

[Gixy]

Hi all,
I just finished an "oscillo-clock" based on the the Dutchtronix board and a 3BP1 CRT. It works, but there seems to be a bad contact in the basement of the tube, a plastic part where the contacts are going out of the glass tube. After a variable time, from few seconds to several hours, the heater shuts off and I have to shake, press, turn the tube in order to recover. I don't know if it is possible to separate this plastic sockett from the tube to try to fix the problem, knowing that it moves a little.
I'm sure that our CRT gurus will have ideas to direct my repair process.
Thanks in advance,
Denis

[tronde]

I don't know if it is possible to separate this plastic sockett from the tube to try to fix the problem, knowing that it moves a little.

A close-up picture of the socket would be useful.

[T3sl4co1l]

The base is soldered on -- thin wires soldered into the regular sized pins mounted in the plastic part.

Sounds like one of them is loose or broken?

Tim

[oldway]

Try to reflow the solder of pins 1 and 14. (NB: at your own risk !)

[chris_leyson]

I've successfully done this repair on a shorter 3 inch CRT, un-solder the wires (solder pump or wick or both) straighten out the wires and remove the base. Solder thin wire tails onto the existing wires and thread them back through the hollow pins, Apply some epoxy put the base back on, wait for epoxy to set then remove the wire tails and re-solder the wires to the pins. Also done it on a few octal valves that had loose bases as well. All depends on how easy it is to remove the solder. That reminds me, I've got a small 1 inch DH3-91 CRT somewhere that would make for a nice project, anybody know where I can get a socket for it ?

[Gixy]

Thanks a lot to all for your prompt answers!
@Tim: that's what I think too, the question being now how removing the plastic part to reflow the solder Inside the pins
@Chris: how do you unsolder the wires as they're not visible? See a close-up view of the socket here below.
@oldway: if I heat pins 1 and 14 to reflow the inner solder, you mean there is a risk to break the tube?

[oldway]

Thanks a lot to all for your prompt answers!
@Tim: that's what I think too, the question being now how removing the plastic part to reflow the solder Inside the pins
@Chris: how do you unsolder the wires as they're not visible? See a close-up view of the socket here below.
@oldway: if I heat pins 1 and 14 to reflow the inner solder, you mean there is a risk to break the tube?

There is no risk at all to break the tube.
But if the wire is broken, it will not make contact even when the tube is cold.
You will have then to dessolder all the socket and repair the broken wire.

[tronde]

Inside the central cylider of the socket you will find the glass tube used to evacuate it when manufactured. This is the most fragile spot of the entire tube. Take care not to wiggle the plastic part too much if you need to remove it.

[chris_leyson]

Hi, sorry I remember one tube base where the wires had been bent over the top of the pin and then trimmed so they kept the tube base in place even when the solder was removed, I think with most wired tube bases they just cut the wire flush with the end of the pin. From your photo I can see solder on the ends of the pins and as tronde said, if you have to remove the base don't wiggle or rock it sideways too much just in case you break the glass sealing pip. Good luck with your repair.

[setq]

Wear safety glasses when handling CRTs . These old tubes go pop rather spectacularly.

[Gixy]

Again thank you all for your excellent advices. I'll keep you in touch with my repair attempts.

[richnormand]

When I was servicing TVs in the 70s I did come across that type of CRT problem a couple of times.

Removing the base was always the last attempt and a last ditch effort (unless the base was already loose).
As mentioned before, the glass nipple is very fragile and will break easily. Also, previously mentioned, is the risk of implosion (I remember a 27" CRT that imploded when movers tipped a TV hard on its back and the protective dome caved in. The whole insides were destroyed with shards of glass. The front screen was intact. Complete write off, although most of the time the tube would remain intact. You cant tell ahead of time)

Most repairs were successful by heating the pin slightly until too hot to put your finger on it. Then massaging some rosin flux inside the pin if it was not occluded. Then, heating fully with the soldering iron until you could hear bubbling and see the flux fumes, then using 0.030" solder fed inside from the back of the pin until "full" (Surface tension nearly filling the inside of the pin but not overflowing. You don't want to short the other pins)

Good luck with it.

[chris_leyson]

Good point richnormand, I just read the OPs post again, if it's on the heater pins then it's probably dry joints because the heater pins on most modern CRTs are going to run hot and that will eventually lead to a dry joint. Reflow the heater pins with a bit of Tin/Lead solder Damn, I was thinking of solid steel pins coming straight out of the glass envelope as they do on modern CRTs but as the base pins are connected via thin wires then over heating and dry joints may not be the issue.

[setq]

I've got a 3JP1 which is similar and the pins (also 1, 14) run less than 50oC even after a couple of hours. That shouldn't affect the joints.

[Gixy]

As you can see on this picture, it seems to be some sort of snap rings at the bottom of the pins. May be a way to disassemble the base? I'll first try to heat the pins hoping that this will reflow the solder Inside, ans if not try to disassemble...

[Ian.M]

No snap rings - just a ridge round the hollow pin, so it resists being pushed into the base to handle the socket insertion forces.  The pin will have been formed from sheet metal - probably brass - with those ridges, and was probably swaged into the base insulator before assembly. There's certainly something other than solder holding the pins into the base as they have to withstand the pulling force of removing the tube from its socket. 

The ONLY way it can be dismantled is desolder every pin, check each wire can be wobbled entirely freely then attempt to separate the base from the tube.  This is an absolute last resort, if the alternative is scrapping the tube.

When working on it, if you attempt to remove the base, wrap the whole tube apart from the base in cloth and securely tape it in place, with the absolute minimum length of neck exposed in case anything does go wrong.

[Gixy]

You must be right Ian, these are not snap rings. How do you think I can desolder the pins, just heating them with iron or hot air?
And thanks also to warn me about implosion risk.

[Ian.M]

You'll need a good desoldering gun with powered vacuum.  You *MIGHT* get there with an ordinary solder sucker and a high power iron to heat the pin from the side right at the tip,  but it increases the risk of cracking the tube considerably.    If that's all you've got and reflowing the heater pins doesn't fix it, you are probably FUBARed.

Desoldering it will go a lot easier if you can find some polished stainless microbore tubing (e.g. a large hypodermic needle) that will slip over the wires but still fit within the pins.
First clear as much solder as possible.  Lightly oil the needle, slip it over the wire end and use it to ease the wire away from the pin wall while reheating the pin.

[albert22]

Once you desolder the pins you might have to heat the base to soften the glue that keeps the base fixed to the glass.
good luck

[N2IXK]

Back "in the day" there was a special tool available to repair these type of problems with poorly soldered CRT pin connections.  It was a crimper that would fit over the offending pin and then press a "dimple" into the side of the pin to attempt to restore the connection.  It was specially designed NOT to distort the OD of the pin, so the socket would still make good contact.  Here's an ad for one from 1959:

http://www.americanradiohistory.com/hd2/IDX-Service-&-Sales-IDX/Archive-PF-IDX/IDX/50s/PF-Reporter-1959-09-OCR-Page-0070.pdf

Good luck finding one of these guys today, though! These style CRT pins went largely obsolete by the mid 1950s, being replaced by hard wire pins sealed directly into the glass.

The wire in the pin is a special material called "Dumet", which is a copper clad nickel/iron alloy. If the copper cladding is thin or corroded, getting solder to wet the connection is a real pain.  I would suggest heating the pin and using a vacuum desoldering tool to remove as much of the old solder as you can, then using fresh solder with a few drops of liquid rosin flux applied INSIDE the pin to make the repair.  Be sure not to build up so much solder on the outside of the pin that the socket won't fit anymore.

Removing the entire base to make the repair is DEFINITELY a last resort, especially if the base is still firmly attached to the glass.  Rethreading all the leads through the base pins is no fun, and that's assuming that you don't break any of the brittle wires off or crack the glass envelope when removing the base. The base cement is a thermoset resin, and heating it won't do too much to soften it, but may crack the glass from thermal stress. A replacement base harvested from a dud tube is a big help here, so you can carefully remove the bad one piece by piece and desolder the pins one at a time.

[Gixy]

Excellent! I'll try to work on it tomorrow. See what I found relative to this "pin crimper": definitelly hard to find today!

[richnormand]

Excellent! I'll try to work on it tomorrow. See what I found relative to this "pin crimper": definitelly hard to find today!

Well that brings back memories.

We had one of those at my shop in the 70s. We stopped using it altogether in favour of the resin flux and solder method I described earlier.
Seems the trouble would come back about a 6 months to a year later with just the crimp. Since we had a fleet of nearly 100 rental TVs we had good service records and data dating back to the early 60s (Yes that was a thing in those days).
Mind you nothing compared to bad contact troubles on the mechanical RF coil-banks strips on the tuners.

[Gixy]

Hi guys,
Yesterday night I couldn't wait and proceeded as richnorman wrote:
- removing the solder with my Pace desoldering iron. It has a tip with exactly the right diameter. Solder entirely removed in 2 seconds. Thank you Mr Pace!
- then put some liquid rosin flux into the pins
- finally put 0,03" solder and reflow from outside with my soldering iron
- remove traces of solder outside the pins and reconnect...
- tada! It works : I let it all the night long switched on and this morning it's still alive.
You're the best. My very best thanks for your help, I appreciate a lot. EEVBlog is the place!
Sincerelly yours,
Denis

[tronde]

Nice

Can you give us some more pictures of the complete clock?

[Gixy]

Yes I will when I'm back home on Tuesday. By