Help alignment with 148 gtl

[kaos513]

It is sometimes hard to be sure if a variable inductor is bad or not. You can test to see if it is open or shorted, and it is very difficult to test for a core to coil short without special equipment and good specs, but in my experience with radios, the most common problem with them is the core is cracked/broken due to people using metal or ceramic screwdrivers to adjust them. The ferrite core is very brittle, and will crack very easily, and sometimes it will be difficult to tell without removing the core.

If you suspect the inductor to be bad, disconnect one of the leads and check for continuity, and a fairly small resistance, such as 2-3 ohms. No continuity is a bad inductor. If you have continuity, it is most likely something wrong with the core. If you can still turn the core, turn it until it comes out, and see if there is a crack in the core. If you pull it out, and the core is cracked, you can sometimes pull the core out, remove the broken portion, and insert it in backwards and it will still work to get the output you want. If you can't turn the core from the top, you have to remove the inductor and screw it out from the bottom.

If removing the broken portion and reinserting the core upside down doesn't work, you will likely have to replace the inductor, unless you have spare cores, which is unlikely unless you work on radios and remove the cores from the parts chassis you have.

Anyway, there is more to it than that, but that would cover 95% of all inductor faults.

core is in great condition

 

[PoDuck]

Could this be a inexpensiv meter and loading the circuit.

Good call. It's been so long since I have seen a low impedance meter that I don't think about the impedance of the leads much.

 

[PoDuck]

core is in great condition

If that is true, it is unlikely that it is the inductor. First, see if you can find the impedance of the meter, because as low_boy said, you could be loading the circuit with a cheap meter.

Have you checked the voltages on the legs for the VCO? Specifically pins 8, 9 and 10. They should be 8V, 7.3V, and 4.02V respectively. TP9 is connected to pin 5, so don't worry about that one. Keep in mind though, I don't have the schematic for your specific radio. The one I am looking at still uses the MB3756 regulator. Therefore, the voltages might be different, but they should be relatively close. Especially if it still uses the UHC-007 VCO module.

 

[kaos513]

I will test all pins later and post results.

 

[kaos513]

got it to work had bad solder joint by the pll chip all is good now,the way i found it was i bought a cheap 14 dollar endoscope from ebay and hooked it up to my tablet worked very well on looking for bad solder joints.

 

[Low_Boy]

Kaos513 Neat I never knew there was such a thing. Kind of like a USB magnifier but you can yuse it with your phone it looks like.

 

[kaos513]

yes its a mini microscope they call it

 

[kaos513]

https://m.ebay.com/itm/500-1000X-8-...hash=item1ca6151379:m:m-Gie04hZZo6U5h61ofcNbw

 

[Robb]

Nomadradio had this very subject just within the last week BTW. He pointed out that if the voltage setting on the coil was with the core all of the way to the top; then internal fixed capacitor in that coil has gone open.

But what you've described above as a problem is something I've seen a few times before. When the loop osc circuit has an open condition between it and VCO, it will spike the VCO voltage. Diagnosis: bad solder joint, open trace, or open component. Well; that is my best guess anyway.

 

[sonoma]

Kaos , I am glad you found the problem. a bad solder joint is a normal problem now days on so many radios with poor quality control at the facility building radios today.
that little scope you used is what I went to using about 4 or 5 years ago. you can look at solder joints and cracked traces with this unit and it brings them up so big and clear on your computer it is hard to miss the bad area. I use mine with my laptop most of the time. would not be with out it now, and so cheap to buy also.