I picked up an MFJ 868B and have an issue

[Unit 75]

Also the board is mfg for both TO-92 and SOT-23 packages. You can do your measurements on the empty holes (TO-92) so you don't short anything.
The above voltages were taken with a 9v battery and the unit turned on but not hooked to anything.
-75


added... ok, here is a MFJ-868B I opened up for above measurements. AGAIN..the green orange and brown wires for forward/reverse going to the rear board where the SO-239's are mounted were Not soldered in. Just pushed through the holes and bent over some. I tacked them in and then snipped off the excess. Quality Control done by JB/17. Also, look at the RED wire used as a ground instead of a black wire. Very professional for a commercial item. So I thought I would check the calibration of the meter as compared to one of my Bird 43's and my Peak Reading meter. On the 20W scale the pot would not adjust high enough to read the proper wattage. As found (with the pot cranked to max was 40% out of tolerance. That's huge!! 200W and 2KW scale were out 18% but were adjustable to reflect the correct readings.

 

[Crambone]

Ok... with your 9v battery installed and the red on/off button on, I want you to take some voltage measurements for me. I installed a 9v in one here and took some measurements for you. See if you get something close as battery voltage will differ some. Let me know how you make out.

Q1 (2n3904) collector voltage should be around .672v
Q4 (2n3906) emitter= 14.7v base= 15.4v collector= .7v
Q5 (mpsa13) collector= 15.3v

So I seen this a bit late but my 9Vdc isnt getting past Q4 and my 12Vdc goes past it in all directions. I tok my measurements in 12Vdc today and put them on the drawing.
Note that with 12Vdc supplied I anm getting 12Vdc to Collector of Q1 keyed but thats it.

 

[Crambone]

View attachment 30853 View attachment 30854 View attachment 30855 Also the board is mfg for both TO-92 and SOT-23 packages. You can do your measurements on the empty holes (TO-92) so you don't short anything.
The above voltages were taken with a 9v battery and the unit turned on but not hooked to anything.
-75


added... ok, here is a MFJ-868B I opened up for above measurements. AGAIN..the green orange and brown wires for forward/reverse going to the rear board where the SO-239's are mounted were Not soldered in. Just pushed through the holes and bent over some. I tacked them in and then snipped off the excess. Quality Control done by JB/17. Also, look at the RED wire used as a ground instead of a black wire. Very professional for a commercial item. So I thought I would check the calibration of the meter as compared to one of my Bird 43's and my Peak Reading meter. On the 20W scale the pot would not adjust high enough to read the proper wattage. As found (with the pot cranked to max was 40% out of tolerance. That's huge!! 200W and 2KW scale were out 18% but were adjustable to reflect the correct readings.View attachment 30851 View attachment 30852

I will take these readings later after the grandkids leave cant do ANYTHING that involves thought with them around!

 

[Unit 75]

I understand. Family comes first

 

[Crambone]

I understand. Family comes first

Thank you for your help I’m new to this but learning!

 

[Crambone]

Ok... with your 9v battery installed and the red on/off button on, I want you to take some voltage measurements for me. I installed a 9v in one here and took some measurements for you. See if you get something close as battery voltage will differ some. Let me know how you make out.

Q1 (2n3904) collector voltage should be around .672v
Q4 (2n3906) emitter= 14.7v base= 15.4v collector= .7v
Q5 (mpsa13) collector= 15.3v

Ok I am getting the following with 9vdc batter and meter turned on.
Q1 (2n3904) collector voltage .867
Q4 (2n3906) emitter= 9.1v base= .87v collector= .87
Q5 (mpsa13) collector= 1.1v

 

[Crambone]

View attachment 30853 View attachment 30854 View attachment 30855 Also the board is mfg for both TO-92 and SOT-23 packages. You can do your measurements on the empty holes (TO-92) so you don't short anything.
The above voltages were taken with a 9v battery and the unit turned on but not hooked to anything.
-75


added... ok, here is a MFJ-868B I opened up for above measurements. AGAIN..the green orange and brown wires for forward/reverse going to the rear board where the SO-239's are mounted were Not soldered in. Just pushed through the holes and bent over some. I tacked them in and then snipped off the excess. Quality Control done by JB/17. Also, look at the RED wire used as a ground instead of a black wire. Very professional for a commercial item. So I thought I would check the calibration of the meter as compared to one of my Bird 43's and my Peak Reading meter. On the 20W scale the pot would not adjust high enough to read the proper wattage. As found (with the pot cranked to max was 40% out of tolerance. That's huge!! 200W and 2KW scale were out 18% but were adjustable to reflect the correct readings.View attachment 30851 View attachment 30852

 

[Unit 75]

Q5 looks bad. You should have approx. 9V on the collector using the battery and approx. 13-14v on the collector using the wall plug.

also check the voltage on pin4 of the TLC2274 IC.

 

[Crambone]

Pin 4 is showing

Q5 looks bad. You should have approx. 9V on the collector using the battery and approx. 13-14v on the collector using the wall plug.

also check the voltage on pin4 of the TLC2274 IC.

Ok thank you I tested TLC2274 with 12Vdc and I’m getting 12Vdc on pin 4.

 

[Unit 75]

Good. Replace Q5. I would use a TO-92 case MPSA13. It will probably be easier for you to solder in than the surface mount version. The holes in the board are there for you.

 

[Crambone]

Great thank you. Ya my eyesight isn’t that good!

 

[Crambone]

OK I replaced Q5 and still the same. I also replaced Q1 and Q4. I had ordered the TLC2274 just incase so I installed a socket and the new TLC2274 but still the same. So I decided to take a look at the pentameter for 20 watts and believe it to be bad as Im only getting 5.3k ohms from it not the 25k it shows in the schematic. It also is a different type from the other two that are 500k. Picture included. Could this be causing my not being able to adjust the meter properly. As Im new at this stuff so Im really just guessing. on the 2 500k they say 500k the one that should be 25k only has 10E on the top

 

[Unit 75]

Nope. It's the same in mine and that scale will not adjust properly. I think a smaller value pot will give it a bit more adjustment but not much.

 

[Unit 75]

I also find when I want to check the SWR,,,, the calibrate knob will not adjust all the way to the top. hehehehe

 

[Crambone]

I also find when I want to check the SWR,,,, the calibrate knob will not adjust all the way to the top. hehehehe

I’m baffled now. I hit every solder joint over in the radio. I put 8 watts dead key verified on my Bird and I can’t adjust the 20w potentiometer past 4 watts. The SWR is doing the same thing.