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Help Restoring A 142 GTL with A 2SC2078 Driver Mod
- Thread starter LeapFrog
- Start date
True, i'm about to install a 2sc2166 and pull the 100 ohm bias "add on" resistor as i didn't find 100ohm near that area on the schematic, no reference to this mod found on the net, although some guys have seen this done before.
I'm just hoping it keys after i swap driver in, and that i can set the bias. Time will tell!
when you are getting the backward swing from the radio are you using the built in power supply or an external power supply. I have seen these old radios have backward swing off the internal power supply. it gets old and weak, the cap in the factory power supply could be getting weak. just a thought since you did not say what power source you are using for your test.
Another cause for backward swing is having the AM dead key set too high.
4w or less dead key for best results.
4w or less dead key for best results.
Internal psu, i need more caps on hand!
And thanks Robb It's at 2-3 d.k. now, just swapped in 2s2166 and removed the "added" resistor, it keys less and reverse swings worse, time to set the bias!
I'd check the driver/final circuit of your radio against the schematic to make sure it is intact. When you go to set the bias, just follow the service manual to the letter. If either the driver or final won't bias after you are sure you have set the radio straight, the first suspects are the VR trimmer pots or the biasing diodes.
I need to pry my meter open, no current found at tp8 or tp7, i suspect a blown fuse.
Right now, no bias found lol!
USB, ch 19, no modulation, radio in tx mode and rx mode, no bias found yet
Just like (link =>) this: found in(link ->) this thread.
Only the "tech" had the wires reversed @ tp7 & tp8, same vcc source i think though so it shouldn't matter if i swap em back around.
Opening meter now.
Bad 500mA 1000v fuse in meter, locating my other meter as i don't have a replacement fuse here.
Meter says .41 mA on driver and 1.49 mA on final, I think it's off by a decimal or two, i am using the larger unfused current range of my dmm
qoute: The POSITIVE lead of the DVM goes to the post and the NEGATIVE lead goes on the wire removed from the post. DVM should be set to mA's. Turn off any mic gain and then key the mic.
If the radio normally works in SSB mode; then you must be doing something wrong with your testing procedure . . . -Robb
Robb that's how i got it.
If the radio normally works in SSB mode; then you must be doing something wrong with your testing procedure . . . -Robb
Robb that's how i got it.
Good point, the mA Jack requires a new fuse, should i just jumper it out while i do this bias adjustment
I should be safe? I'm soldering a jumper on the old ceramic fuse!
Driver should be set at ~25mA; not .41mA.
Final should be set at 50mA; not 1.49mA.
It's the range the meter is being used @ I assume the final bias was way hi (150 mA) I'm about to check it in the proper range after I patch the fuse with a soldered jump lead!
Thanks for your help!
- No one is chatting at the moment.
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@ BJ radionut:list'n 50.125 USB...working in shop...also 2m FM Simplex freq's 6.52...6.46 ... 6.55 etc..
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@ BJ radionut:I was look'n your way Evan...was working on some lighting in the garage...you were just "Thr" but w/ fade...you were gone...so did not fire the heater and call+1
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