The 18V regulator is still not directly replaceable with an LT1581 which has an inadequate voltage rating. Replacing either of the 2N1701's with a more modern transistor may well lead to oscillations due to the much higher ft of the replacement transistor.
Bruce Adrian wrote: > Re-read Jim's posts. > > To me it seems clear that he is talking about the 2N1701 Q3 in the > upper right corner of fig. 5-12. > He mentioned that +18 measures high, around 26V. > So, the problem is NOT in the battery charger circuit. > > The purpose of that Q3 is to generate +17.4V (and +7V) from +26V, with > the base being connected to +18V, thus the emitter voltage of Q3 is > +18V - 0.6 to - 0.7V. > > The +18V regulator circuit is on the lower left of fig 5-8, A1A4 Outer > Oven Controller. For a circuit description see 4-40 to 4-44. > > The +18V feed the AC amplifier (A1A2), the +15V through R14 (might be > cooked if run at 26V for extended time) and CR2 on the same board, the > power amplifier (A1A3), the outer oven temperature control circuit > (decoupled +18V), and the inner oven control cuircuit A1A5. > The 17.4V that are derived from +18V feed the dividers. > > Any adjustments make sense only after fixing the +18V supply. > > Actually, Q3 might as well be shorted. I would first remove it from > the circuit to see if the +18V are then correct. > If not, check the voltages at Q9 and Q7 of A1A4. Q9 is mounted on the > oven housing cover. > > Regards, > Adrian > > Bruce Griffiths schrieb: >> christopher hoover wrote: >> >>>> The 2N1701 is a general purpose transistor rated at 60V, 2.5A. >>>> >>> I've mentioned this before, but it bears repeating. >>> >>> If you are having trouble with an old school linear power supply, in >>> many cases you can replace the TO-220 PNP pass transistor *and* the >>> reguatlor circuit (based on a 723 or whatever) with a modern >>> integrated regulator in TO-220 such as an LT1581. Strip the regular >>> board of everything except for the the input and output caps (if they >>> are still good) and wire up a pair of resistors to set the voltage. >>> Add a couple of jumpers to complete the circuit. And then you are >>> good to go. >>> >>> -ch >>> >>> >> That probably wont work in this case. >> The supply is actually an NPN discrete darlington buffered 32V zener >> with a current limit transistor to set the battery charging current to >> one of 2 values. >> With the battery removed the supply output should rise to 32V - 2Vbe - a >> diode drop, ie about 29.8V or so. >> The series diode is required to isolate the battery from the regulator >> output when the main fails. >> It should be much quicker and easier to just find suitable transistors. >> >> Bruce >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
