GrindingThud Posted January 9 Report Posted January 9 Update after listening all day with it closed up - temps in the base of the heatsinks are at least 77°C, current is 14.2 mA. Yep, it’s hot. The batteries crapped out in my IR thermometer, so I used a high end contact meat thermometer between the fins, lol 🥩. The heat sinks are not in contact with the case…I may try the aluminum bar mod if it gets too hot.
judo Posted January 9 Report Posted January 9 (edited) 21 hours ago, GrindingThud said: Congrats! 21 hours ago, GrindingThud said: That front panel light is a bit bright…may need to tone that down a bit… 🤓 I have changed it too and now I can not see it in daylight so I plan to change it again for a couple of years 😞 Edited January 9 by judo 1
Pars Posted 5 hours ago Report Posted 5 hours ago (edited) Question time: One of the people I built a mini dynalo for sent it back to me for repair. They apparently had something stacked on top of it with it on for a day. When they turned it on the next day, no workee. When I got it, the first thing I noticed as only 2 of the 4 pcb leds were on, and sure enough, the positive reg (amb) had bit it. I went ahead and removed that and ordered another reg. While waiting for that, I powered it using my bench supply and didn't find anything wrong that I could find. DC offset was fine, bias was fine. Did a diode test on all of the output transistors with no problem. When the replacement reg got here, I went ahead and put it in after seeing no issues on the bench supply, and it turned on fine. This weekend, I was going to get it finished up to return the amp, and went ahead and let it run for an hour or so with the heatsinks on, but much of the case missing. When I went back down to check on it, the offset was around -900mV and then I noticed that 2 of the leds were off. Positive reg bit it again. I went down tonight and measured the +/- rail currents at +288mA and -278mA after running for quite awhile on the bench supply. These regs are supposed to handle up to 1A each, and have thermal protection. I took a heat gun and noticed the current was going up pretty fast when I was heating the output section; up to over 350mA after a short time and climbing. I did not wait to see how far it might go. I have no idea how hot one of these could get with something sitting on top of it, but I'm guessing quite hot. I know the regs current capability will vary with heat and how much voltage they are dropping, which in the case of these is 4V(24V in, 20V out). I'm injecting the bench power on the electrolytic 100uf caps. There are (4) 100uf tantalum polymer caps following the electros, which may not like heat much? I don't know. Amb's regs are up to $30 ea. with $10 shipping, so I don't want to keep burning these up. Just looking for ideas on where to look next? Edited 5 hours ago by Pars
ang728 Posted 1 hour ago Report Posted 1 hour ago did the old regs still working individually after removed from mini dynalo? 4V difference looks fine even a bit too much for amb σ78/79 , I would check the DC voltage ,also check output waveform on scope to see if it's oscillating when symptom occurs
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