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
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