B7971 Shorted Segments

[Jim KO5V]

Hello,

I took two spare B7971 tubes out of the cabinet to see if they still worked. These tubes were always questionable, but I hoped I would get lucky. One is DOA - which I expected. The other tube is nice and bright, but the two vertical right-hand segments are shorted together. These are segments 2 and 3, which are pins 5 and 6, and they measure a dead short.

When it is displaying a zero or an 8, it looks almost normal, but those two segments seem a bit brighter to me. The 2, 6 and 3 are screwed up. The microprocessor in the two-digit clock is not happy, and the error is shared by the other tube if the same number is being  displayed on both tubes - this is not something that I'm too concerned about since the error goes away when I swap in a good tube.

Has anyone had any luck "whacking" the tubes in any particular direction to try to relieve this problem (by whacking, I mean slapping it into my palm)? Is there something else that I can try?

Thanks.  Jim

[Jeff Walton]

If you search this group, there are a number of posts with photos of of successful repairs. I've had some success (>50%) but you need to consider that attempted repairs may not be successful and you risk the tube.  

The older style 7971s are more susceptible to being damaged by repair efforts, as they are not internally supported as well.  Older style means tubes with the wired backplane or tubes with the center post.   The PCB style internal construction is better supported in the envelope and stands up better to the hard shock needed to dislodge the overlapping cathodes.   Mechanical overlap failures are generally the ones that are successfully fixed.  Tubes that have been driven too hard with cathodes that are delaminating will generally fail again after operating for a short time.  "Fixing" those tubes tends to be temporary.  

Good luck, it's great to get a win. 

Jeff 

--
You received this message because you are subscribed to the Google Groups "neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+...@googlegroups.com.
To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/03dbd726-23bb-43d3-a070-72430707800an%40googlegroups.com.

[Jim Faulkner]

Thank you Jeff,

 

I'll check the archives and try something. I think it is not an early tube, so maybe I have a chance. It does not have the "pin top"

 

Best regards,

 

Jim

 

You received this message because you are subscribed to a topic in the Google Groups "neonixie-l" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/neonixie-l/vGvyfHH_M6I/unsubscribe.
To unsubscribe from this group and all its topics, send an email to neonixie-l+...@googlegroups.com.
To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/67a8220c.920a0220.258f1e.0d3b%40mx.google.com.