22-04-2012, 09:36 PM
(22-04-2012, 07:53 PM)Joe Wrote: I've thought about the current-limiting thing myself, and indeed have one I use for charging batteries, but have never known what to set it to plus I've never understood how current can be limited without cutting the voltage.
Ah - when the current limit is reached, the output voltage does indeed fall. Sometimes like a stone! But that's the point - better that than let the smoke out
Quote:I'm trying to be philosophical about it and think that at least it's a chance to play about with alternative transistors. The current arrangement works but obviously wouldn't for long so I need to find some that can handle more power.
That's the spirit
Actually, once you've sorted the quiescent current, the BC327/337 would probably be OK. If you leave things as they are, but simply put bigger transistors in there, then all you'll do is eat batteries...
One thing to check; with at least 2 examples that I've looked at, the biasing arrangements around T3 were different to the manual. Rather than the NPN AC127, there was a PNP something or other... As a result, R13 was connected to a different part of the circuit. Anyway, it's worth checking - what was the T3 that you removed - an AC127 or something else?
Quote:Edit: Thanks, Lawrence I've added the circuit to my earlier post from this afternoon. I'm not for giving up by any means - I've said before that you learn far more from your failures than your successes. I'm loath to shell out for new 'Correct' transistors as, as Mark says, the actual problem remains un-diagnosed.
These transistors are getting harder to find, so it's a wise idea to experiment with others...
Out of interest, how do you know the originals failed? I must admit that I'm not sure how T3 could...
Also, don't forget that AC127s et al aren't totally immune to the "tin whisker" disease...
BTW, I know I sound like a clever-clogs all the time, but if it's any consolation, I'm struggling with what should be a simple fault that I've fixed many times in the past. I get more than my fair share of difficult things here! And the trouble is, it's easy to forget the countless easy jobs that sailed through when these things are getting you down!
Cheers,
Mark
