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I'm hard-pressed to see that you missed anything. But I do remember RCI telling me about ten years ago to set MOSFET idle current to 10 mA. per final/driver. This was in response to 2995DX radios blowing up IRF520s a week or two after replacement. Just how that advice might apply here is...

There should be a crystal that's been added to provide the added frequency coverage. It will be wired to the switch along with the big,fat crystal that's just inboard from the MB8719 PLL chip. The extra-channel switch will select one or the other crystal. I recommend setting it on frequency...

The old saw goes "Measure once cut twice. Measure twice, cut once." Lost track of how many times I advised someone to check the base voltage feeding to a new replacement final before soldering that lead to the pc board. Shoulda taken my own advice. Customer states no transmit from his Cobra...

Plug it into an outlet and plug an incandescent bulb into its other end. If the bulb flashes, that's what this thing does. 73

That relay is normally mounted with a saddle that slides down over the ceramic end and clamps the flange to the rim of the hole in the chassis deck. The saddle has a screwhole on either side, like the mounting plate for a twist-lock filter cap. Seems to me the last vacuum relay I used that...

Have you tried turning down the mike gain to see if this stops the screech? If it doesn't, that's important. And if it does stop the screech, the cause is upstream from the mike gain control. 73

Q67 is a surface-mount power transistor. It's a pain to remove safely with no damage to foil traces. We use a workaround that bolts a plastic-body TO-220 style transistor to the heat sink and three wires connect to the pc board, taking the place of the failed surface-mount part altogether. I...

Not to put too fine a point on it, but there are literally more than a dozen radios that say "Cobra 29", each with different suffix letter. Over the 50-plus years since the first 23-channel '29' was sold the internal design has evolved considerably. So just which 29 is having this problem? 73

Just tell him you posted pics of the carnage on line. It doesn't need to be repaired. It needs to be built. Assuming, of course, that the pc board hasn't been damaged too badly. Might be able to keep the ferrite transformers. More than once I have quoted a repair estimate that was double the...

First thing we do with this kind of base amp is power the amplifier side from a bench power supply. If that part of it works, the old transformer comes out. A switchmode brick just fits. There is *NO* point to repairing the original voltage regulator. It's just accident prone, and lacks decent...

Has to be a trimpot somewhere for each pair of transistors. I'd say the gate voltage should be set for about 200 mA idle current, keyed with no drive. The low gate-voltage reading is more likely a trimpot that's broken or set too low. And if there's only one trimpot, a burned resistor on the...

You pop the colored lens off the front of the button. A tool to reach the bulb inside is a problem. Best bet is a short length of rubber tubing with the inside diameter just a little smaller than the bulb's diameter. 73

Pretty sure D2 and D3 rectify the plus and minus 15-Volt rails. Don't see which one is for the postive side and which is negative. Looks like they were replaced with type 1N4007. Should be perfectly okay for that circuit. Current drain won't strain the 4007's 1-Amp rating. 73

I remember reading about LCD driver chips long ago. They stressed that the drive waveforms had to have a perfect 50 percent duty cycle, to prevent any DC offset. They said display life would be shortened if that spec was not perfect. Even a tiny net DC component would degrade the display...

The "170" number was used by more than one supplier, each with a different letter prefix. The Motorola "HEP" or Workman "WEP", or "R170". Or International Components Corporation "ICC170". It's a 2.5-Amp rated 1000-Volt rectifier. They're not so common now. We use the generic 1N5408 3-Amp...

The switches most likely served to expand the frequency coverage above and below the legal 40 channels. To get the normal 40 you probably need connections that were being made through those switches. I'll see if I can find pics of what that section of a PC409 radio should look like before that...

Holy moley! I guess one accurate measurement really is worth a thousand (wrong) expert opinions. 73

I would unplug it, discharge the HV and power the relay circuit from an external 12-Volt DC supply. A small supply with a current limit around 1 Amp is a sort of swiss-army knife tool for this kind of troubleshooting. Gator clip it to the standby switch to power the relay alone. Keying it with...

Hey, you're welcome. That's what we do here. 73

We could back up a step and have a look at the radio's printed circuit board ID number. I haven't seen this model in a long while, don't remember that detail. Ranger recycles the internal design of radios, using the same set of guts for a dozen or more brands and models. This one may be the...