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I have never tried to analyze this computer board. The presence of the EEROM puzzles me. The factory service folks told us in 1995 that the cap was good to retain data for a week. If the EE were used for that, it wouldn't matter if the capacitor ran down. I think the "update EE while the cap...

The GNF is the electronic equivalent to taking the cardboard tube from a roll of paper towels and covering your ear with one end of it. It's an audio band pass filter. The sound of the thing doesn't seem to appeal to anyone I have found yet. 73

Post Script: You wouldn't take a 5-Amp mobile radio and power it from a 30-Amp power supply with no fuse protection, would you? Sure enough this is what the factory sold you. Or sold the original owner. But the mobile-radio circuit board at the heart of this base station has no separate...

First encountered Tom Kneitel in Popular Electronics. His column included reader questions. At the time LSD was new and in the news. A reader wrote in asking if there was any electronic way create a psychedelic experience. Tom told him to find LSD (Large Silicon Diode) with a wire attached to...

14 Volts DC. This is a little like "how many horsepower can I get from my 2-liter 4-banger?" Depends on how long you want it to last before it croaks. Higher supply voltage will goose the wattmeter a bit, but never enough for anyone at the other end of the conversation to tell any...

Look beneath connector CN604. It's peeking out from under the row of header plugs. 73

Now if only someone (else) would come up with a generic bit-mapped LCD or (gasp) OLED display, decode the data stream feeding the factory screen, cobble up sprites to mimic the original screen's dedicated symbols and hack the code to mimic a factory display to the radio's CPU. Sounds like more...

Older transformers would have a separate breakdown-voltage rating for the center tap. Blew up a few old military transformers that were meant to be used in a full-wave circuit with the center tap grounded, or close to ground voltage. I wired them to a full-wave bridge and the secondary winding...

The schematic makes it appear that C4 does this job in the DX radio's computer board. Capacitance is 220uf. Should be the biggest one on the board. Never have figured out just why they stick with this method. The board has a 93LC46 chip. It's a non-volatile EEROM chip. Seemed to me this would...

It's a darn good thing somebody wants new radios, or the industry would collapse. 73

Turns out Amazon has a chinesium version. https://www.amazon.com/Eliminator-Aluminum-Canceller-X%E2%80%91Phase-Receiver/dp/B09CM9F247/?tag=worradfor-20 Lots cheaper than what's being quoted for the MFJ. 73

This transformer was probably not the only thing that burned up. Don't quite see how to get less than 1200 Volts from it judging by the markings. D&A used the same transformer in all their sweep-tube base amplifiers. The HV secondary should be around 650 Volts depending on your local line...

Used to hear a south african beacon on 10 meters 3 solar cycles ago. Almost never heard any hams from that region. Haven't conventional beacons been superseded by WSPR and such? Been out of the DX loop long enough to not really know. Makes me wonder if your noise is a point source that could...

When I'm confronted with a symptom I can't explain, the place to look first is the power supply. This radio has two switched regulated 9-Volt power sources. This crop of the circuit board parts-placement diagram shows two bare jumper wires near the center of the crop. J26, the one towards...

Found the pic. If your preamp relay looks like this one, you can totally avoid removing the printed circuit board from the amplifier this way. Won't have a preamp any more, but the flaky preamp-relay problem will be a thing of the past. The wires are fairly thin. Removing a strand from a thin...

Here's a problem with miniature toggle switches I had to discover the hard way. They're made two different ways. The outer two terminal lugs sticking out the rear of the switch each have the contact point on the other end inside the switch housing. The center lug connects to the "seesaw" common...

The part number printed on the relay is your only hope of getting a drop-in replacement. Relays that size don't always have the same pin assignment. The specs for the original part will define what can drop in and replace it. Just need that number to find the specs. And if you just don't need...

Try to find a car without a LCD display. Gotta wonder how long those will turn out to last? Not as long as my 1999 Ranger, most likely. 73

Just don't drive them hard enough to break the spot weld on a grid wire. The loose wire end is less a hazard in a base amplifier. If the loose end of a grid wire gets jostled and touches either the plate or grid, bad news for the other two tubes. Maybe. Far likelier in a mobile. 73

Holy Moley! A typo. In a file decades old. Oops. Yeah, D52, not 32. Been doing that job mostly from memory long enough to totally miss that error. And once we show the procedure to a new tech, they can find the components by sight without squinting at the screen-print callouts. Thanks for...