J4 is your High/Med/Low Tone switch. Maybe the solder bridge adds an additional capacitor across the top of the Volume Control?
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959 DX GALAXY-NO SOUND
- Thread starter hammer0630
- Start date
J4 is your High/Med/Low Tone switch. Maybe the solder bridge adds an additional capacitor across the top of the Volume Control?
After popping the case on the 959, it too has the exact trace oddity so it seems that it's just the way it's made.
OK now, more testing today and didn't get audio but I'm pretty sure at this point that the cb/pa switch is working as it should if my testing was correct.
With ground led of dvm to a tuning can and probing each pin of j18 at the control panel with the jacks connected I can get continuity readings as I switch from cb to pa. At the ground pin I get a solid ground as it should so the ground is there too.
Went further and was able to test the switch after completely disassembling the front panel pcb to be sure. All assembled with fresh solder.
I get continuity from the Audio ic to j18 at the speaker pa plug end too so where to start next... capacitors, diodes?
OK now, more testing today and didn't get audio but I'm pretty sure at this point that the cb/pa switch is working as it should if my testing was correct.
With ground led of dvm to a tuning can and probing each pin of j18 at the control panel with the jacks connected I can get continuity readings as I switch from cb to pa. At the ground pin I get a solid ground as it should so the ground is there too.
Went further and was able to test the switch after completely disassembling the front panel pcb to be sure. All assembled with fresh solder.
I get continuity from the Audio ic to j18 at the speaker pa plug end too so where to start next... capacitors, diodes?
Which audio IC does it have? The TA7222 or TDA2003? Pin 4 is the input pin on the TA7222, whereas Pin 1 is the input pin to the TDA2003. Did you touch a metal screwdriver (that you are also touching) to the input pin to see if you get a buzz or hum sound from the speaker?
Tda2003 ic, listed readings on those Post #8,9. I tried to be as detailed as possible. Zero audio at all from the speaker in cb,ps, talkback. Absolutely nothing. From a monitor radio it produces audio that coincides with both radio meter and external test meter. Receives per the on board meter from monitor radio. Just no audio of any kind from internal, external or pa in any mode.
I'll regain thoughts and continue tomorrow.
All help is greatly appreciated.
It is my fear that you have a couple of swapped (even Damaged) jumper headers.
Here's why...
See BLUE GREEN YELLOW HEADER?
That is from your SPEAKER GROUND section in the back...
The one that Selects whether to use CB / PA or (combined) RB
You'll need to pull that header from the FRONT PANEL board, and short out the YELLOW and GREEN wires in that header together - and then try and see if you hear a THUNK or a pop from the SPEAKER when you turn it on - now that ground for that speaker has been established.
IF no sound - PHYSICALLY SHORT OUT CB TO CG terminal in the rear - and then if you hear a pop or a thunk - you know you have problems with the front PANEL BOARD and it's HEADER, and it will have to be pulled and inspected.
I have had to replace VOLUME /Talkback pots because of bad caps (C177 or C184 per your MOSFET) either way, the Audio Out cap failed - replaced it, but also took out the Volume control and others like Squelch - so this is not over yet - we're just trying to get speaker physically hooked up - then try and track down receive.
(Which hopefully will return without having to go deeper into this)
Here's why...
See BLUE GREEN YELLOW HEADER?
That is from your SPEAKER GROUND section in the back...
The one that Selects whether to use CB / PA or (combined) RB
You'll need to pull that header from the FRONT PANEL board, and short out the YELLOW and GREEN wires in that header together - and then try and see if you hear a THUNK or a pop from the SPEAKER when you turn it on - now that ground for that speaker has been established.
IF no sound - PHYSICALLY SHORT OUT CB TO CG terminal in the rear - and then if you hear a pop or a thunk - you know you have problems with the front PANEL BOARD and it's HEADER, and it will have to be pulled and inspected.
(Which hopefully will return without having to go deeper into this)
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This could also be from the GNF (General Noise Filter) board that this radio sends audio thru then onto Volume - that's at J5.
But the odd part here is you don't hear any "hiss" or noise from the Audio amp during any of this test - even a simple hum from touching the probe to the audio line in.
You did check to make sure the speaker is 8Ω ohms right? No shorts from its wires to the speaker core to its spyder cage?
Ok, another approach to this...
Areas of Similar Color should also show continuity amongst that color.
VERIFY YELLOW HEADER WIRE IS Connected to BOARD GROUND (Continuity) - if not - then stop and find out why you don't have ground on the MAIN PCB Header that CB/PA/CG - the one in the back by the speaker jacks.
But the odd part here is you don't hear any "hiss" or noise from the Audio amp during any of this test - even a simple hum from touching the probe to the audio line in.
You did check to make sure the speaker is 8Ω ohms right? No shorts from its wires to the speaker core to its spyder cage?
Ok, another approach to this...
Areas of Similar Color should also show continuity amongst that color.
VERIFY YELLOW HEADER WIRE IS Connected to BOARD GROUND (Continuity) - if not - then stop and find out why you don't have ground on the MAIN PCB Header that CB/PA/CG - the one in the back by the speaker jacks.
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Receive audio and transmit audio on any of these Galaxy/Connex/Mirage/(even Uniden PC122) are totally separate from each other. You can have perfectly good transmit audio and no receive audio, as in your case, or the other way around, too (RX ok, no TX audio). Did you check or change the capacitors around the speaker audio amp (TDA2003) ? How about the transistor that "mutes" it when in transmit ? The schematics on CBTricks only shows the TA7222 variation, not the newer TDA. Is it an add-on board that retrofits the TDA to fit the TA designed main board, or did they redesign the speaker audio section of the main board for the TDA?
So, I pulled up the schematics for a radio that uses a TDA, a Magnum S980, there is a transistor that "shorts out" the audio input pin of the TDA when in TX (Mute), there might be a similar transistor on your radio, check to see if this transistor is there, and if it is bad.
So, I pulled up the schematics for a radio that uses a TDA, a Magnum S980, there is a transistor that "shorts out" the audio input pin of the TDA when in TX (Mute), there might be a similar transistor on your radio, check to see if this transistor is there, and if it is bad.
Thank you again for the pointers. Andy, will taking a shot at your testing methods to double check again. Maybe I misses something.
NZ8N, I'm adding your advice to this as well and according to the schematic (pictured below)for the 939 I'll be looking at the areas around IC8 also
Can't thank you fellas enough, being this far into it I don't want to turn back now.
NZ8N, I'm adding your advice to this as well and according to the schematic (pictured below)for the 939 I'll be looking at the areas around IC8 also
Can't thank you fellas enough, being this far into it I don't want to turn back now.
Attachments
This is from the DX939, see if there is a voltage on Pin 2 of the TDA, they appear to be "biasing" this pin to mute the TDA by applying +8v TX through R216 (10k) and D75 to Pin 2. Check C178 (47uf @ 25v) too.
this may be a bit of a crazy idea, but since you have both a working 959 and a non working 939, there is a test you can do that will at least point us in the right direction.
look at J5.
that is the connector that connects your volume and squelch pots to the PC board.
first thing to do is just check and make sure it's fully seated. disconnect it and make sure that no pins are bent or pushed back like they made a mistake at the factory.
J5 OK?
yes?
moving on...
you can disconnect J5 in both of your radios and swap them.
it might be a bit tricky or even somewhat impossible to get the radios oriented in a way that the 959's J5 can be plugged in to the 939's socket, but if you can, try it.
like this:
both radios powered up, volume up, squelch down, speaker connected etc...
pull both J5 connectors from their PC board sockets.
plug the J5 from the 959 in to the PC board socket for the 939.
did anything change?
if so, then your volume control, squelch control, or the connections to them are bad in the 939.
no change?
try it the other way and post the results.
IDK this may be too wacky but who knows...
LC
look at J5.
that is the connector that connects your volume and squelch pots to the PC board.
first thing to do is just check and make sure it's fully seated. disconnect it and make sure that no pins are bent or pushed back like they made a mistake at the factory.
J5 OK?
yes?
moving on...
you can disconnect J5 in both of your radios and swap them.
it might be a bit tricky or even somewhat impossible to get the radios oriented in a way that the 959's J5 can be plugged in to the 939's socket, but if you can, try it.
like this:
both radios powered up, volume up, squelch down, speaker connected etc...
pull both J5 connectors from their PC board sockets.
plug the J5 from the 959 in to the PC board socket for the 939.
did anything change?
if so, then your volume control, squelch control, or the connections to them are bad in the 939.
no change?
try it the other way and post the results.
IDK this may be too wacky but who knows...
LC
Good evening gents and thank you all again for your help.
I'm pretty confident in saying the front panel switches, jumpers to main pcb are all good after thorough testing. Moving on.....
So here's what we have at ic8 and others mentioned by nz8n
Pin 2 - .82
D75 - .82 on the cathode side and nothing on the anode side
R216 - nothing
Figured I'd move next to chasing the Audio trail to and from the Audio ic.
I followed Pin 2 output from ic8 all the way back to j18 checking caps jumpers etc, found a dead C177 electrolytic. 330uF and will have to see if I've got one tomorrow.
Finally, at least found something!
You fellas are awesome for offering to help a not so competent guy.
L.C.
That's a great idea, thought about it throughout the day while at work and couldn't wrap my head completely around it haha. That's on the to try list if the current path goes nowhere..
Thank you sir
I think what he meant was, if you could pull the button/switch/pot assembly for the Volume/Squelch/etc... from the known good radio, if it is a similar hookup, temporarily transplant it into the place of the defective radio to test. Not necessarily the whole faceplate switch assembly, just the Vol/Sq part.
all it would do is point toward the problem.
if swapping the jumpers solved the problem, then you would know that the problem is somewhere after the volume control.
if swapping the jumpers did nothing, then it points to a problem before the volume control.
LC