Kiran,
A sawtooth waveform would point to a bad C1. A waveform of a much higher frequency would be from an oscillation and more superimposed on the DC. As long as you are going to do some soldering anyway, you should just replace the 7805 with the drop-in switcher that you received from Tayloredge. It is MUCH more efficient. You could also replace C1 at the same time since you are already working on it. Saves you the work later if it is deteriorating. Bypass caps are also a good practice for circuits with high frequencies. Many modern board layouts that work with much higher frequencies (probably not in your clock) build-in circuit traces that are engineered to act in the same manner as a bypass but it won't hurt anything in a clock design to add the bypass caps to a power rail. Many years ago, during my time with Texas Instruments, I sold hundreds of thousands of the little 78xx and 79xx series regulators into a lot of different applications. They were a new and novel solution for cheap and dirty regulation and efficiency was not a big deal back them. Today, the small drop-in replacements for the 78xx series are a much more modern and elegant solution when there is a small power budget. Jeff Walton From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On Behalf Of Kiran Otter Sent: Saturday, April 04, 2015 1:52 PM To: neonixie-l@googlegroups.com Subject: [neonixie-l] Re: Need help with a tubehobby clock overheating I should have said if I see oscillation from the 7805 that Jeff mentioned, pointing to a bad C1. I may just replace it regardless. Kiran On Saturday, March 28, 2015 at 7:55:48 AM UTC-4, Kiran Otter wrote: Hi folks, glad to find this group! I've had a Tubehobby clock for several years, the NCV2.1 with the IN-18 tubes. In the past Jonas has helped, and I even shipped him the main board for him to repair, but he hasn't responded to my last request for help, so I thought I would ask here. Recently, I started to notice that other digits in the tubes were partially lighting up, and eventually the fuse blew. My assumption was that the K155ID1 drivers had started to go, so I ordered six of them off eBay, and tried replacing them.. which isn't hard, everything is socketed. Well it didn't help, so I contacted Jonas. Jonas suggested replacing C6, which I did and it appeared to fix the problem. Maybe a month later, I started to notice the left most digit was faintly showing numbers, and seemed to be influenced by the next to right digit. So I thought perhaps the drivers I got from eBay weren't good, so I swapped them around, trying to see if it made any difference. Unfortunately, I trashed the two original driver chips that came with the kit. So far swapping the drivers around among the six I have, hasn't changed anything.. or if it has, the digits lighting that shouldn't be have moved from tube to tube. Well I let the clock run like this for a week or so, and one day I just happened to feel around the voltage regulator U1 (L7805CV).. and it's blazing hot. I put a temp probe on it and it's running at 140F in open air, and when I built the clock, I epoxied a heatsink to it. It never ever used to get this hot. In fact the clock has run for years in a closed enclosure with very little ventilation. It just never produced much heat at all. I swapped both driver chips for two others, and it still gets just as hot. When the clock shuts off the display at night, the temp drops to just above room temperature. So my guess is has to be one of two things I replaced; C6, or the driver chips. I think it's the drivers, and I'd like to get a pair from somewhere reputable so I can at least rule them out as the problem. I've seen some that appear to be ceramic, instead of plastic cased.. claimed to be 'milspec' but I donno if that's BS or what. Any help is appreciated! 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/db144a82-9537-4bb7-9a3b-6f1536af8c65%40googlegroups.com <https://groups.google.com/d/msgid/neonixie-l/db144a82-9537-4bb7-9a3b-6f1536af8c65%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/5520bca5.88196b0a.532c.14fc%40mx.google.com. For more options, visit https://groups.google.com/d/optout.
