148 gtl issue

[kopcicle]

That "should be" PIN #7 (PIN# 8 may work as well) of the SO42P remember that's in AM TX . If the junction of C128 (positive side) and L32 (small choke) near L31 has 6.8V in AM TX then looking at PIN# 7 on the SO42P should give 7.8xx MHz. If not try at the cathode of D53 going into L48 transformer if you have a 10x probe. Its easy to "load" these circuits just by measuring them so double check for 27. 185 MHz TX CH 19 when finished .
Some of the above may differ from the 148GTL as All I had on the phone was the 2000GTL . If you have a schematic or manual you should be able to figure it out.
Remember to do the alignment in order so the 10.240 and 34.xxMHz synthesizer adjustments are done before moving on to the TX Oscillator

 

[kaos513]

This made in china 148 is different.

 

[Robb]

This made in china 148 is different.

I have one too, and it aligns pretty much the same way.

However, I don't align the output osc that way. I key the mic up with the radio running into a dummy load and use a sampler on the radio's output to the freq counter. Set L31 to set AM first w/o any mic gain/dead key carrier only on CH 20; should read 27.205000mhz.

Then USB/LSB using a 1khz audio tone into the mic (mic gain halfway up) to get the proper output freq set. On Ch 20 LSB, tune L30 until the radio's output reads 27.204000mhz. On CH 20 USB adjust CT2 until the radio's output reads 27.206000mhz. That simple.

http://freesound.org/people/klangfabrik/sounds/28636/

 

[kopcicle]

This made in china 148 is different.

Was on the phone and missed that , sry ....

 

[loosecannon]

kaos, i also use the same method that Robb does, and it works well.

i would add a couple of things to the instructions though.

If you are using a freq counter that has a BNC connector on the front (im pretty sure you are) then you do not want to connect its probe to the antenna jack and key the mic into it.

You will want to pull the driver and final bias wires from their test points first.
this will keep the transistors from amplifying but will allow the small signal through.
yes, you can do the SSB tests with them in place, but i find it easier and safer to just pull them while doing this part of the alignment.

the other thing is that you have to be sure that your 1K tone is actually 1000 KHZ, because if the tone is off freq, your radio will be also.

I think Robb linked you to an online tone that you should be able to trust, but if you are using a tone gen that you built, or is built into one of your pieces of test equipment, you will need to measure its freq using your counter before moving on.
If the tone is off, and you can't adjust it; just compensate for it with your final output freq.


on a side note, mike just posted a video showing a cheap device you can buy that will allow your freq counter to read these low level signals so that you can do the alignment by the book. (both methods result in the same level of accuracy if done right)

here is a link:


hope this helps,
LC

 

[kaos513]

Another issue, i have audio and power on lsb,usb. but no modulation on am very low and distorated.

 

[nomadradio]

Does your radio have a metal-tab power transistor mounted to the aluminum rear-panel plate? The one I'm talking about has three wires leading to it from the main pc board. This is your AM modulator transistor. If it's been clobbered, it can cause this symptom.

Do you have a way to test it?

73

 

[kaos513]

No its plastic type or silicone type.

 

[kaos513]

I installed the new part it improved a little but still no modulation in am as it should be.

 

[kaos513]

Does your radio have a metal-tab power transistor mounted to the aluminum rear-panel plate? The one I'm talking about has three wires leading to it from the main pc board. This is your AM modulator transistor. If it's been clobbered, it can cause this symptom.

Do you have a way to test it?

73

Got it to work repalced the part and realigned the radio, but still working on getting power up now.

 

[kaos513]

Meter is now moving after alignment but my volatge on channel 19 is 3.2vdc channel 40 is like 3.7 vdc shouldnt it be like 4.2?

 

[nomadradio]

Lotsa different voltages to measure in that radio.

Which one of them do you mean?

73

 

[kaos513]

I aligned it by putting my volt meter to tp 9 and adjusting L19.

 

[Low_Boy]

Had a vol control do this, hit it with some cleaner and it cleared up.

But it is also possible that a ceramic disc cap has become microphonic. Not likely; but possible.

I would have to say a bad electrolytic capacitor

 

[kaos513]

No was a bad transistor as for the wattage readings i have yet to figure out why so low on channel 40