[MRCA] [MMRCG] AN/PRC-70 continued pt.3

[jkarlow at comcast.net]

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:  <mailto:jkarlow at comcast.net> jkarlow at comcast.net

Tel/Cell: 248-961-2034

 

 

 

From: MMRCG at groups.io <MMRCG at groups.io> On Behalf Of Ray Fantini
Sent: Monday, November 21, 2022 1:37 PM
To: MMRCG at groups.io; MRCA <mrca at mailman.qth.net>
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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[jkarlow at comcast.net]

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