Texas Ranger TR696F SSB RX ok, AM TX ok, SBB TX very weak

[nomadradio]

Is the receiver sensitivity up to snuff? If not, maybe there's a hint. And it hears weak signals like it should, this is just a red herring.

73

 

[David Springmire]

Is the receiver sensitivity up to snuff? If not, maybe there's a hint. And it hears weak signals like it should, this is just a red herring.

73

Good evening and thank you. Initially the receive sensitivity was very poor too. I aligned the PLL and the receiver, that got the receive to near spec. Next, went to align transmit and noticed AM RF power was low. I thought that was the only issue but found the mod where they removed the on board AM power pot, disconnected the SWR cal pot from the circuit and put it in place of the on board AM RF power pot. I re-installed the on board AM power pot and left the SWR cal pot disconnected for now. That got AM working but then found the SSB very low and been troubleshooting the cause since then.

 

[nomadradio]

The point in asking about receiver performance is that if both transmit and receive are weak, it's being caused by a resource that both are using. This points to the VCO that controls the receiver and transmit frequency. I don't have the schematic handy, but I think the VCO output is L20. If it won't peak properly, this will hold back both receiver and transmit performance.

73

 

[David Springmire]

Good evening all, I hope I don't offend anyone with the long post but if you'll bear with me at the end of this I do have a question. Just thought you might be interested in the result. I want to thank you all so very much for your quick responses, ideas, feedback and all around encouragement on this "project" I'm sorry for the long delay in responding, was waiting on parts and honestly was so discouraged I didn't want to touch a thing. Through a lot of prayer and encouragement the problem was found! After brandon7861 explained the theory of operation of the SSB APC and the measurement results, then thought to Gman's "other mods" question (I didn't find anymore thank God). I revisited nomadradio's resonance point. I borrowed a friends working Galaxy DX-959 and went back to the TX mixer The 959 isn't exact but "close" (I was able to align the RX sensitivity to near spec so it led me to believe the VCO was OK). This unit uses a TDA6130-5 mixer but the board layout and connections seem to be those of a SO42. I looked at the data sheets for both and emphasize they are not interchangeable at least not in this configuration. I've got a Saturn here too that uses the same TDA6130-5 IC and it's layout is different than both. Using a spectrum analyzer I marched through the mixer making comparative measurements between the DX-959 and Texas Ranger TR-696F SSB and kept coming back to the 10.695 MHz level being low by >20dB. While all the coils did have "peaks" the level into pins #7 and #8 were consistently low. DC voltage measurements were OK. The modulator output was also lower but only marginally D25 was turned on but was seeing that huge drop between FL3 input and output. Finally I pulled L44 and replaced it with L44 from the DX-959 and bingo! that was it. Even though it had a peak I guess it wasn't enough LC to increase the gain of the mixer output. I attached a couple of pictures and would like to ask a couple of questions.

First I want to preface by saying I do this as a hobby, I'm retired and handicapped I don't do it for profit. The person I'm repairing this for says it should do 40W, the manual says 12W, with adjustments at maximum it's doing almost 15W, there have been no mods to the power amplifier I see. So, I don't know where 40W is possible 1). Does anyone know what power it "should" produce? I'm using 30mVrms as audio in from an arbitrary waveform generator. 2). and second most importantly does anyone know where I can get the L44 coil? It's stamped 12255. Thank you again for your kindness and especially wisdom and patience.

 

[David Springmire]

Oh, one other point if you're curious or maybe you all know the answer the NG L44 measured 1.2uH with the slug in the position shown and Z measured about 370 ohms.

 

[nomadradio]

TDA6130 is a new name for an old part, same as the Siemens S042. Siemens got out of the chip business and the new owner of the patent issued a number using their own corporate "TD" prefix and part number. Same chip, new number.

40 Watts from a DX2547? He has it confused with the DX2517 model. I have seen that one show 40 Watt peaks on AM, but not sideband. It has two of the single final transistor found in the 2547. A legal 40-channel radio only has one final transistor. Two of them more-or-less double the transmit power compared to a FCC-legal 40-channel radio. Those radios are typically labeled "10-meter" radios. They have transmit power and frequency coverage well beyond what a legal CB can have. Pretending that it's a ham radio is a ruse to get it through customs.

A 2547 might show 20 Watt peaks tricked out for max, with the power supply voltage turned higher than the 13.5 Volt spec.

Barkett's "goldeneagleradios.com" site lists the 12255 coil.

https://stores.goldeneagleradios.com/if-transformer-ift-12255/

73

 

[David Springmire]

Good morning, thanks so very much! I ordered the 12255 coil. I'd like to get (2) but looked like only (1) available. I emailed on the off chance they may get more in. Thank you too for the output power and mixer information! Now to try and get these mods in order, align it and Good Lord willing finished. I truly appreciate all the help and wisdom. It's a lot of fun to work on these (keeps the mind working) frustrating at times but fun. There's so many nice people on this site. Great to know you're all still out there.

 

[nomadradio]

Great to know you're all still out there.

Yeah, I'm just another dinosaur waiting for the asteroid.

73

 

[HavaV10]

great job on getting it fixed. I just got one of these TR696F for free and seems to work ok. Haven't hooked a watt meter up to it yet but will soon and test it out. So L44 was the problem child? I'll have to remember that if my SSB power output is low.

 

[nomadradio]

Alignment is the first trobleshooting step for low transmit power. And if the only problem is a coil someone randomly "adjusted" way off of its peak setting, you fixed it with that alone.

And if alignment alone doesn't cure a low-power issue, the behavior of those slug-tuned coils becomes a diagnostic point. A coil that won't peak like it should points you to the circuit with the fault.

73

 

[HavaV10]

First things first. Verify you have 13.8v at the power supply G. If you are using a 12v supply, the numbers in the manual will not be possible.
View attachment 74773
Lets talk about SSB. Since this radio has an automatic power control (instead of just a transistor switch saturating the passthrough regulator), transistor Q56 serves to hold the output at 12.5v.

Lets assume you did have 12.5v at TP7 (A). D103 is a triple-junction diode, so assume it drops .65v * 3 = 1.95v of that. 12.5v - 1.95v = 10.55v at point B. The voltage divider R271 and R270 cut that in half and present 5.275v to the emitter of Q56. Point D is .65v higher at 5.925v. VR17, in combination with the RF Power pot form a voltage divider that sets this base voltage at point D and holds it steady.

Think of Q56 as a voltage comparator. With the base held constant, as RF pulls down on the final supply A, Q56 wants to conduct harder, and this pulls down on the darlington pair (Q54 and Q55) to work to raise that final supply back up. It is a constant battle around that loop to hold A at 12.5v.

The two diodes at F serve to isolate this APC bias voltage from the AM carrier voltage, both of which must share the same RF Power control.

Lets stop there and see if you can figure out why you can't reach 12.5v. If this was too hard to follow, take some voltage measurements at all those points in SSB with no modulation.

Brandon were can I find the full view of this schematic for the 696F base. Looking for it online but have had no luck. Need wiring diagram for the 696F base switch panel wiring. Thanks.

 

[TM86]

IF it uses the EPT069610Z main board then this should get you close:

Download Galaxy DX 959 Service Manual | ManualsLib

www.manualslib.com

 

[HavaV10]

IF it uses the EPT069610Z main board then this should get you close:

Download Galaxy DX 959 Service Manual | ManualsLib

www.manualslib.com

thanks I'll keep that one but I need the 696F base schematic. Putting wiring back to stock on the switch pcb board and someone changed it putting in extra frequencies. So I'm needing the wiring diagram to put the switch panel back to stock.