Cobra 148GTL_ Taiwan w/ commstat 200

[Smokinone]

I am beginning to work on an early Taiwan 148GTL. It has had a lot of things done to it as far as putting in the Commstat 200 VFO. The receive is great, as all 148's. There is no transmit however. The CB/PA, tone hi/low, and brt/dim switches have been disconnected. ?
I pulled this from my late father in laws collection of goodies. The face plate has some discoloration as I have done a quick polish on it, and as you can see still has the discoloration. The box it was in looked to have been in water at some time.


It also needs to be glued back on or possibly a new one if the project goes well. It also has the chassis board power connector removed? for some reason, and was hard wired with some zip cord with the negative side grounded to the chassis. I removed that, and have a new connector on the way. But I did use the zip to do an initial test to see if it received and transmitted.


I have replaced all the electrolytic caps, and am in the process of removing and applying new heat sink compound or silicone insulators. I also had to replace the clarifier pot as the shaft pulled out of it when removing the knobs, bummer, but I had one in a front mic 148 that is parts/donor.
That brings me to a couple of question concerning the 1306 and 1969 driver and final. I show good on the driver and the 1969 on my Sencore Super Cricket tester. I also used the LCR-T4 type tester.
Results are:

original 1969 and 1306 respectively





I don't see an issue with them although they differ from a new and pulled 1969 and 1306

New 1969


pulled 1306



I'm not going to get too crazy on the troubleshooting until I get the new power connector installed as I tend to be clumsy at times, I already blew one fuse.
I do have questions though on the driver and final. Neither one in the radio seems to be shorted, just different HFE from new, used, pulled. I have seen the 2SC2166 used as the driver with the 2SC1969 final. Is the 2SC2166 able to be swapped with the 2SC1306 without modification or issue? The specs look very similar other than the 2166 seems to be a little beefier. I have new 2166's but not the 1306. Since the original ones in the radio are not shorted,should I use those as I am testing as they don't appear to be shorted?

Here's another little goody, a 5V power supply for the Commstat 200. Uses a 33ohm resistor with the 7805 regulator. I will clean this up and insulate the leads as I go along...again as I tend to be clumsy sometimes.



One last thing, I think this has an NPC mod done to it. I have never put one in, I like to keep things as stock as I can. If someone recognizes the mod, could you let me know? Thanks.



As I progress with this, I'm sure I may need some help if at all possible. I have received a ton of help here in guiding me in the right direction lately, so thanks all for that.

 

[Smokinone]

Been doing a little work that i can do without power.
Technical bulletin 1266 done, I hope a 1w 16V zener will be OK. I think I've used them in the past, been to long since I've done one.

TR24 was missing. I replaced it with a 2SC945P, I didn't have an "A" version. I hope the HFE is OK at 287. I don't know what the "A" version HFE is. I don't know if this effects too much down stream. One mod I have seen wants the R124 and R126 replaced. Mine are stock @10k.

Insulated the leads from the 7805 regulator.

What I think ? is a NPC is D47 lifted and a 100k ohm, resistor in series.

 

[Smokinone]

Scouring the net I have the belief that the 2SC2166 is drop in for the 2SC1306.

I removed the 100K resistor and restored D47 to it's original state. Tied to VR6. This is for the meter evidently.

Replaced a missing and bridged C108. Has to do with the audio. Now back stock.

Installed the insulator on the 7805 with a silpad. The mica insulator was brown, either from heat or age.
I also put a piece of wire behind the loom for the Commstat to keep it from pulling out, I know, tacky blue silicone.



I also noticed C226 on the driver is missing. I need to check and see if this is supposed to be in place. I imagine it is, I certainly don't know why someone would remove it.



I should have the power connector tomorrow, so that's when all the fun will start.

Thanks

 

[Smokinone]

This coffee can "shield" was installed when I initially opened up the radio as well. It's held in place with some banding it looks like. I suppose trying to keep RF out of the 7805 Commstat power? Who knows.

I did put the C226 back in as well.

 

[Smokinone]

I am at the point of where I need a little help here on this 148. Please

I have no transmit, but do have good receive. The transmit and receive LED shows it's switching ie: it turns green and red for rx and tx.

TR41 and TP7/8 switch from 13V to 6V when keyed in AM, stay@ 13V on SSB

I started by checking the voltages of the PLL and the 3756 regulator. They are all where they are supposed to be according to the specs I have.

Checked TR35 which is the TX/RX and I get E=7.5V C=13V B=7V at rest. Keyed up, all the voltages go to 0V

I have put in the original 2SC1306 which tests good, and a new 2SC1969 as the pulled one showed good, but had a low HFE. Not sure if it makes a difference as nothing is working on that end of the radio at this point.



As far as the alignment went, all the test points are right on after some adjustment going through the process. I have 27.185 at the antenna connector, I was initially low on voltage for pin 1 on the PLL but that adjusted out to the 3.5V as needed.

TR39 shows RX 0V and on TX C=8V E=1.2V B=.5V

TR36 driver is C on TX 13V RX 6V, E on TX = .6 RX .2... shows same on the TR38 driver.

When I adjust the driver bias, TP8 still connected, TP with ammeter, I get no adjustment and it is @ 15ma

Adjusting the final bias, I can get it adjusted to 50ma with TP7 off and meter in line with TP8.

Checked the MV1Y with a diode tester and it shows good, the MV13YH tests as an unknown part. When I check across the MV13YH in my Cobra 2000, it shows as a 474uf capacitor. Am I looking at a bad MV13YH in the 148?

I still have no RF output. AM or SSB


That is where I'm at so far. Any pointers would be greatly appreciated.

Thanks.

 

[Smokinone]

I put a new 2166 driver in. I get no adjustment, as with the 1306, on USB for driver bias adjustment. I get the 15ma on AM position which is not according to the manual.

Thanks

 

[Smokinone]

OK, poking around the driver area and VR9 with the VOM, I found a bad solder connection. Actually looked open. I hadn't been in that area of the board with anything I have done so it most likely was the issue with the output when I started on it. So I now have about 2 watts on Am and showing 4 whistling in to the mic on SSB...more adjustments to be made.

Wish my eyes worked better, even with my big light it's sometimes hard to see things...I'll blame the glare from the bulbs

 

[Smokinone]

OK, poking around the driver area and VR9 with the VOM, I found a bad solder connection. Actually looked open. I hadn't been in that area of the board with anything I have done so it most likely was the issue with the output when I started on it. So I now have about 2 watts on Am and showing 4 whistling in to the mic on SSB...more adjustments to be made.

Wish my eyes worked better, even with my big light it's sometimes hard to see things...I'll blame the glare from the bulbs

View attachment 49578

The 2 watts AM and 4 watts SSB are all I can get out of this. Pots are adjusted to the max so I still have issues somewhere.
Thanks

 

[NZ8N]

2SC1969 is/should be an NPN. The 2SC1306 and 2SC2166 drivers should also be.
Have you set the bias on the Driver and Final?
The power being low, could be 1 or more of the transformers in/around the SO42P TX mixer IC, may need realignment.
On what frequency are you transmitting on, center or towards the band edges?

 

[Smokinone]

2SC1969 is/should be an NPN. The 2SC1306 and 2SC2166 drivers should also be.
Have you set the bias on the Driver and Final?
The power being low, could be 1 or more of the transformers in/around the SO42P TX mixer IC, may need realignment.
On what frequency are you transmitting on, center or towards the band edges?

Thanks for the input. I didn't catch the NPN PNP change-up.

That was some kind of goofy reading on that 1969. I had a new TC7 meter charging, so when I tested it again it was correct.

I went through the alignment process in the SAMS, the VCO transmit alignment on the frequencies specified. I was on 19 for most of the alignment, except in one area that wanted me to be on 40. With this Commstat maybe I should have tuned at 40?

I came back to this after dinner and put the original 1306 and 1969 that I had replaced with what I thought were new and correct components. I have a couple of bags marked RF Parts that had the new 2166 and 1969's in them These were what I had found in my late father in laws stash. I Assumed they were originals when I put them in. I know he hadn't messed with radios for probably 15-20 years ago, so I thought they were NOS. Evidently these were the ones they were going around that were fakes. Not that RF Parts sells fakes, it's just what the bags were marked. I have personally bought several components from RF Parts without issue.

Onward and upward. After installing the 1306 and 1969 I originally pulled, I set my bias once again, and it did look better as far as adjustments when setting the bias.
Now I am getting about 4W on AM, and 14W on SSB with some swing.

Thanks again.

 

[Smokinone]

I should amend the title as I found out the Channel unit is a Commscan, not a Commstat as I have been saying. I'm afraid to clean any more off as the lettering disappearing as it is now.

Thanks for looking in, and the help. I just wanted to correct this confusion.

One other tid bit. Evidently this Commscan has issues with static. I had noticed it changing channels or when I went to move, or even touch the controls, the unit would change the frequency. I found CBTricks manual and in the instruction set it mentioned the unit doing this, and just turn the unit off to reset. Then they say something like, nothing wrong if it does this.

The clarifier is out of control touchy, I will look at a 10 turn Bourns to cure it. I haven't checked the swing on it yet, but will.

Thanks

 

[cbdoodler915]

That's a lot of time on the 148gtl oldie radio.
Oldest versions yes got 2sc1306 & 2sc1307 as other bases.
I could never get a 2SC1307 to work when replacing it with 2SC1969
something differ about them 2 parts 1307 & 1969 .
But at 4 watt am and 14watt SSB be glad.

 

[Holydvr]

They are indeed worth the time….