[TenTec] Orion A9 board operational thory
dukeshifi at comcast.net
Tue Sep 10 23:09:55 EDT 2019
I have an Orion A9 board that has gone must.
All of the electrolytic are new so not there.
The issue is that, even though I replaced the defective 4.85 volt Zener diode in the base of Q5, the output voltage is stuck at 6.7 volts.
When I look at the bases of Q4 and Q5, there is a strong 25 KHz “square” wave. As near as I can figure, this design applies this signal intentionally to the bases of Q4 and Q5 in hope that the in-phase signals at the bases will cancel out since Q4 is PNP and Q5 is NPN.
That’s the only reason I can see for this design over a simple 7805 regulator for the 5 volt line…
In any case, I replaced both the transistors in the amplifier, Q1 and Q2, and also Q4 and Q5.
Since I had one, I also replaced the -20 volt inverter chip.
I am running out of parts to replace.
Does anyone actually understand this circuit?
If so, some assistance would be appreciated.
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