Kiran,
If you get your scope running, check the output of U1 (7805 regulator) and look for a very flat DC. If you see any type of sawtooth or superimposed oscillation, replace C1. You can use a any higher value than 10uF as long as it physically fits and has a high enough voltage rating. Any visible oscillation superimposed on the output pin could cause the overheating and also could cause the phantom digit illumination as well as other issues. Just as was mentioned in a previous post regarding C6, C1 could also have dried out and a heated board in the same area will accelerate the dryout of any nearby electrolytic caps. C2 is also filtering the input to the 7805 and in the direct vicinity of your hot board. If it is dried out, it will also cause unwanted behavior. Jeff Walton From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On Behalf Of Kiran Otter Sent: Sunday, March 29, 2015 12:56 PM To: neonixie-l@googlegroups.com Subject: [neonixie-l] Re: Need help with a tubehobby clock overheating Something I want to note about how I used a heatsink; I epoxied it to the tops of the cases of M1 & U1; traditionally you'd bolt it to the back of the component but at the time I couldn't figure out a better way, and I had heatsink epoxy, so I just plastered it to the tops of the two components. It's been like that ever since I built the clock, and never did it get so hot that you couldn't touch it. Warm, yes. I don't know how it could have become conductive across the cases of M1 & U1.. if it did, that's a neat trick. But removing it certainly seems to have made some difference. Using a laser temperature probe, M1 seems fine.. but U1 definitely seems cranky.. and it's heating the board up all around that entire end to ~110F. Again, I never noticed it getting this hot. To answer Johnk's question; the heatsink and epoxy weren't touching anything metallic, and I originally added it because I thought M1 & U1 were getting pretty warm from the start when I built it, and figured it wouldn't hurt to add it. But maybe over time.. it started to conduct between them somehow. I don't know. Jon; thanks for that info. I'll try one of the 7805 alternatives you mentioned. Nick; I'll drag out my scope and see if it even still works, and see if I can't check the 7805 with it. I might have a question or two on using the scope. :D So far, right now with a little fan blowing over the M1/U1 area.. the whole thing is keeping cool. Barely running above 90F anywhere I check. If I turn off the fan, it shoots up past 120F. I turned the fan back on at that point. Niek; I re-enabled the leading zero, and still see the same thing. In fact when going through the settings, I was able to catch the attached pic of the right most tube showing what was in the next-to-left tube. So it seems to go both ways. Kiran -- 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+unsubscr...@googlegroups.com. To post to this group, send email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/508e5b80-f513-4cfb-9d71-8a46ab09022e%40googlegroups.com <https://groups.google.com/d/msgid/neonixie-l/508e5b80-f513-4cfb-9d71-8a46ab09022e%40googlegroups.com?utm_medium=email&utm_source=footer> . For more options, visit https://groups.google.com/d/optout. -- 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+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/55185807.07976b0a.7b4a.ffffe5b5%40mx.google.com. For more options, visit https://groups.google.com/d/optout.
