Texas Star 696 Base (Galaxy 959 single final) no transmit, no reading at TP5 during alignment

[Lkaskel]

Good Afternoon Men,
So I have entered the deep end of the pool with this radio. I am navigating way beyond my knowlege but I somehow think I'm close. I have this Texas Star 696 base that has the EPT069610Z board in it. For a schematic I am using the Galaxy DX-959 from 1997 (attached) and it seems to line up perfectly. I am also using an RCI 2950 V3 radio as a reference. The 2950 is not exactly the same as it is surface mount but the layout/logic seems similar enough.

The issue is no transmit. The driver and final are fine. As a troubleshooting tool I went thhrough the alignment with the 959 alignment instructions (attached) and when I got to the TX mixer stage I had no 10.695MHz at TP5 with the radio in AM and in TX with the shorting board removed. I started to troubleshoot this issue and was able to find 10.695 at the emitter of Q46 (output of the 10.6975 crystal). I followed that to the input of IC6 (AM612) pin 3. I have it at C147 (see below) on the crystal side but not on the IC6 side. I did pull C147 and verify it is good (it was) and I replaced it as well. The voltage on the crystal side of C146 is 2.42vdc and 3.7 on the IC side. I compared this to the 2950 in the same scenario. On the 2950 I do have 10.695 at pin 3. The voltage is 2.07vdc in the crystal side and 7vdc on the IC side.

I am trying to determine what I do not have RF on the IC side of C147 and aqm wondering if the lower voltage has anything to do with it. Should I pull IC6 and check without it in place? Also, I have no idea what my next step should be. Any help would be appreciated.

 

[brandon7861]

I have seen the 612 fail, got 3 dead ones in a jar. I've even killed one with a slip of a probe tip.

 

[Lkaskel]

I have seen the 612 fail, got 3 dead ones in a jar. I've even killed one with a slip of a probe tip.

Really? WOW!!! That is good feedback!! The only access I have right now is the one on the 2950. I can do a swap as a test. Where did you get your replacements and feel good about the supplier?

Thanks!!

 

[Cable Guy]

I just bought a 5 pack on Amazon, from China, but I guess it was the last as they now say unavailable. I hope they work. Following thread for any proven suppliers.

 

[Lkaskel]

I have seen the 612 fail, got 3 dead ones in a jar. I've even killed one with a slip of a probe tip.

Ok, So I replaed the 612 with a known good one. It did not fix the issue. Does anyone think that something is loading the circuit down and that is why the voltage going into pin 3 of IC6 is only 3.7vdc? Are there any other thoughts as to why I do not get 10.695 at TP5 when I do have it at C147?

Thanks as always everyone!!!

 

[brandon7861]

I got my replacement of a radio that was butchered and given to me for parts. I will look at the schematic in a little while and see if I notice anything that can do that

 

[brandon7861]

What voltage do you get across pins 4 and 6?

 

[Lkaskel]

What voltage do you get across pins 4 and 6?

Hi Brandon,
With the radio on CH20, AM, shorting Bar removed, in TX I get 7.9vdc across pin's 4 and 6.

Thanks!!

 

[brandon7861]

Ok, So I replaed the 612 with a known good one. It did not fix the issue. Does anyone think that something is loading the circuit down and that is why the voltage going into pin 3 of IC6 is only 3.7vdc? Are there any other thoughts as to why I do not get 10.695 at TP5 when I do have it at C147?

Thanks as always everyone!!!

Forgive me for asking, but are you sure you are on the right pin? When I probe pin 3 on my DX2547, I get 8.8v, but pin 5 has 3.56v. Counting from the wrong end could explain the 3.7v you see.

 

[Lkaskel]

Forgive me for asking, but are you sure you are on the right pin? When I probe pin 3 on my DX2547, I get 8.8v, but pin 5 has 3.56v. Counting from the wrong end could explain the 3.7v you see.

Very fair question!!! I am sure though.

Pin 2 - 3.24vdc
Pin 3 - 3.44vdc
Pin 5 - 6.14vdc
Pin 6 - 7.9vdc

All of the measurements were taken in AM and TX.

Attached is a pic of the bottom of the board with my measurements and notes. So sorry if it is a little confusing.

 

[brandon7861]

Its odd that you would have such a different voltage at pin 3 if it is a known working 612. They didn't note the internal resistance values on the 612 datasheet. Maybe D56 is bad. That diode shunts the 612's output to ground during RX. Maybe something is keeping the RX line too high or that diode shorted.

May as well check C150, I doubt it, but who knows.

 

[brandon7861]

Wait a minute... Pin 5 can affect all those voltages. Check to see if that balanced modulator pot is good. VR6

 

[Lkaskel]

Forgive me for asking, but are you sure you are on the right pin? When I probe pin 3 on my DX2547, I get 8.8v, but pin 5 has 3.56v. Counting from the wrong end could explain the 3.7v you see.

Hi Brandon,
If possible, can you tell me what voltage you get on the non-IC side of C147?

 

[Lkaskel]

Wait a minute... Pin 5 can affect all those voltages. Check to see if that balanced modulator pot is good. VR6

I checked the cap and diode as well as the VR. All tested good.... The mystery continues....

 

[brandon7861]

Hi Brandon,
If possible, can you tell me what voltage you get on the non-IC side of C147?

I will when I get home around 5am.