Ray –

The 1A1A4 Power supply module has two switching regulators +5 volt and +10 volt. If you are not getting any 10 volt output, likely Q1 2N3720 and possibly Q2 2N2907 may be defective. Also please be aware that the 10 volt supply had a fast acting protective Zener diode CR5 1N759 which will short if the regulator goes above 10 volts in order to protect the downstream circuits.

Yes, you will have to remove the metal shields. I recommend solder wick with rosin flux to soak up the solder beads. The good news is that for service testing you can operate the board without its shields. (I would recommend that you replace the shields when you have solved the problem as the switching regulator noise may degrade the noise floor of the receiver.)

73,

Jim

Jim Karlow

KA8TUR

4907 Oakwood Court

Commerce Township, Mi 48382

E-Mail: [email protected]

Tel/Cell: 248-961-2034

From: [email protected] <[email protected]> On Behalf Of Ray Fantini
Sent: Monday, November 21, 2022 1:37 PM
To: [email protected]; MRCA <[email protected]>
Subject: [MMRCG] AN/PRC-70 continued pt.3

Part 3, radios diagnosed while you wait!

X mode connector was installed. Armed with the new TM checked out what’s happening in DC distribution back as far as the A4 DC power supply. It has +24 on its input but no +10 volt output, the +5 volt output is there but not the +10

Next step will be to look and see if there is anyway the +5 volt supply can be working but the +10 would not, that will determine if the issue is in that module or not. If it is in that module will have to figure a way to take a can opener to it.

Had to come back to work so will have to do that tonight.

Ray F/KA3EKH

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