Hi Ray –

I’m glad to hear you were able to get the PRC-70 working!

Regarding the auto tune for transmit, start with using a 50 ohm dummy load/wattmeter with a BNC cable to the BNC antenna jack on the radio. Turn the radio on to LO PWR and select an HF frequency such as 3.885 MHZ. Set mode to AM. Squelch should be off and volume should be Mid-Range. Momentarily press the PTT on the H250 handset and check for a power output reading on the wattmeter of somewhere between 1 and 3 watts. This shows that the transmitter is producing the low power signal which will be needed for antenna tuning. If OK. Release the PTT on the handset. Now turn the Power switch to TUNE and release it. The tune mode should start and last for about 3 to 7 seconds. When the tune sequence stops, turn the switch back to LO PWR and momentarily depress the PTT switch. You should see about 3 watts RF on the wattmeter and you should not hear the beeping tone. If the power output is seen and no beeping is heard with actuation of the PTT, the tuning sequence working. Move the switch to HI PWR and depress the PTT. You should now see somewhere between 9 and 15 watts of AM carrier, indicating that the HI PWR mode is also working. (Remember that in the HI PWR mode, the radio may draw as much as 8 amps). Now you are ready to try the radio out on other antenna configurations as shown in the operators manual.

Regarding replacing the “sardine can” around the supply, you can try it both ways and make up your own mind. As the A4 has switching power supplies, I have found that in many radios you will have increased noise on receive, particularly around 10.000 MHz and some of the 40 and 75 meter frequencies, particularly with weak received signals. I have been replacing the shields after making repairs and finding that, in many cases, it does make a difference.

If you are interested, once the radio is operational, I can send you instructions to do the conversions, if adding LSB, transmit below 30 Mhz and Low Input Voltage shutdown are desired enhancements.

Best of 73’s

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: Friday, November 25, 2022 4:38 PM
To: [email protected]; MMRCG <[email protected]>; [email protected]
Subject: [MMRCG] PRC-70 progress

End result of the RT-1133/PRC-70, thanks for all the help from everyone. After learning what the test points on the motherboard were discovered that the 1A1A4 +10 and +5 regulator were only supplying +5 and not +10. It did have its +24 volts from the filter and -5 volt card. Checking the test point discovered that the +10 volt bus was grounded and after removing the 1A1A4 card the short went away. After way too much time spent removing the tin work from the regulator discovered that C4, a 47 uf capacitor was shorted and dragging down the bus, replaced that cap and now the radio is working. Looks like I may have to read the operators manual to figure out the auto tune deal, is it completed when it beeps three times? Or will the tone go away? Next quest is do I have to reinstall the sardine can around the supply or not?

Ray F/KA3EKH

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