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Low RX volume on dx 44v

ok, man the schematic on cbtricks is a bit confusing, as the transistor voltage chart shows TR39 to be a CW switch, but the schematic shows it to be in the echo supply voltage circuit.


i believe your problem is D77 is leaky or otherwise bad.
this "diode" is actually a varistor, which is a diode that acts like a variable resistor.
part number is MA27T-A. not sure of a cross reference.

i believe that you can test D77 by removing it from the chassis, and testing it with an ohmmeter set to Rx1K scale.
the resistance should show almost infinite, if not "open".
if the resistance is low, replace it.

if that is not your problem, TR36, TR37, TR38, and D76 (5.1v zener) are the parts to remove and check.

i really believe that one of those parts will prove to be the culprit.

i remember fixing a galaxy 959 about a year ago and having to order a 5.1v zener and a 2SA1282 transistor from maycomm, but i cant remember what the initial problem was.
could have been this same issue, but i am very bad at taking notes during a repair.

let us know what you find,
LC
 
IIRC, a MA27T-A is the same as two 1N4148 diodes in series. IIRC, I asked one of the Galaxy techs about this part. He said that they will work as this diode is used just to drop the voltage; so two 1N4148's will sub. Could be wrong; but if you need the part you can call up Galaxy Parts and order one. Otherwise, it is impossible to find on the net.

Think I would replace the electrolytic caps in that circuit first - just for giggles . . .
 
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Yes, the schematic on CB Tricks is confusing. On my board, TR30 is located where the PCB layout says TR39 should be. Either way, the voltages on this transistor are out of whack too.

The base voltage on TR38 is very very close to TX voltage levels, so the radio is definitely trying to switch into TX mode, just not all the way. The TX/RX LED is still green.

I was actually looking at D77 as well, but haven't pulled it yet because it's hard to get to without removing the mic jack.

I can pull D77 from the old junk parts radio, along with the other TX/RX transistors and that D76 zener.

It's getting late again, so I'll pick this back up tomorrow and let you know the results. So close to getting this solved, and don't want to make a stupid mistake because I'm too tired.

Thanks to all for the help again! I'll keep you posted with tomorrow's results.
 
D77 was the culprit! Replaced it with a part from the junk radio and now I have full RX volume!

All the other symptoms appear to have gone away as well, except for the S-Meter jumping up in PA mode. Not overly concerned with that as I don't ever use the PA function.

Next project on this radio will be to perform the 2sc2999 RX upgrade with the 1N6263 Schottky Barrier Diodes.

Thanks again to all for your help and support on this!
 
right on Theta, glad you found it.

there really is nothing like the feeling of actually finding a bad component, replacing it, and seeing your radio spring back to life.

truly a zen moment. LOL

with the 2999 upgrade, its really all about the diodes.
the 2999 may make a bit of difference, but ive never seen it make a big one.

the kits are cheap on ebay so why not buy it anyway, but if you are ordering parts from mouser or some other parts supplier, dont worry about finding a 2sc2999e.

as for the diodes. 1n6263, 1n5711, NTE583, and BAT85 diodes will all work equally well.

best of luck,
LC
 

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