NO TX Audio EPT690010Z board radio

[Low_Boy]

Connex 4800 DXL EPT690010Z board. This board is used in.(Galaxy DX2517, Ranger RG66, RG99, Cobra 148F GTL DX+, Texas Ranger, TR6900, TR6900
Some history on the radio how I got it. It was plugged in backwards Two finals were blown. I do not the two problems happened together. The radio now has 2 new finals and a new driver installed. All traces look good. TR50 and TR51 check good. The radio has great receive and very loud. But I have no transmit audio on side band and AM. Tracing with a oscilloscope I see a little movement all the way up to TR51 and. TR50 also shows a little movement on the scope. Not quite sure if I am going about this in the right way or where to go next.

 

[999]

It's not the 959 board, but the 2517 board.

 

[999]

Here are some links to the 2517 information.

http://www.cbtricks.com/radios/galaxy/dx2517/index.htm

http://www.cbtricks.com/radios/galaxy/dx2517/graphics/dx2517_block_dia.pdf

http://www.cbtricks.com/radios/galaxy/dx2517/graphics/Dx2517sch.pdf

http://www.cbtricks.com/radios/galaxy/dx2517/graphics/dx2517_6900-10z.gif

 

[Low_Boy]

Here are some links to the 2517 information.

http://www.cbtricks.com/radios/galaxy/dx2517/index.htm

http://www.cbtricks.com/radios/galaxy/dx2517/graphics/dx2517_block_dia.pdf

http://www.cbtricks.com/radios/galaxy/dx2517/graphics/Dx2517sch.pdf

http://www.cbtricks.com/radios/galaxy/dx2517/graphics/dx2517_6900-10z.gif

Thank You. I got some wrong info on the Net. I did not have a 959 or any of the above radios to take the covers off and look in. Thanks.

 

[Robalo]

I have no transmit audio on side band and AM

Q53,Q54 OR Q56

 

[Low_Boy]

Q53,Q54 OR Q56

Did not check those will tomorrow
Thanks
Edit. Yes they were checked and Q54 is new.

 

[Robalo]

then fake transistors it happened to me

 

[nomadradio]

Probe the 'scope to pin 1 of IC7. This is the mike amplifier. Your transmit audio branches off three ways for AM, FM and SSB from this point.

If you don't have at least 2 or 3 Volts peak-to-peak mike audio at this spot, your problem is with IC7, or more likely upstream from it. This chip almost never goes bad.

73

 

[Low_Boy]

No fake parts. Most come from reputable sources.

 

[Low_Boy]

Probe the 'scope to pin 1 of IC7. This is the mike amplifier. Your transmit audio branches off three ways for AM, FM and SSB from this point.

If you don't have at least 2 or 3 Volts peak-to-peak mike audio at this spot, your problem is with IC7, or more likely upstream from it. This chip almost never goes bad.

73

I once bought a bunch of Mic amps just in case and have not hat to use one once. I did probe IC7 in the beginning of this project and if I am correct I think the wave looked more like a check mark than a wave. Pretty much looked like that on most everything I probed. I will look at all that again. Thanks Nomad.

 

[Low_Boy]

IC7 is good. I can not get a good clean wave though and the wave is bigger and cleaner on pin 2 of the Mic jack. I will probably look someplace between pin 2 of the mic jack and pin 1 of the mic amp.

 

[nomadradio]

Q39 is the audio attenuator transistor on this board. It's controlled by the AM modulation limiter, sideband ALC and the mike-amp chip's 'compression' circuit.

If there is a fault in the transmit/receive switching circuit the 8-Volt receive-only voltage (collector Q30) may not fall all the way to zero when you key the mike. If it doesn't, this will cause Q39 to shut down mike audio.

If someone has clipped the wrong resistor trying to boost the modulation, it can cause Q39 to kill all the transmit audio. Unsolder the center pin (collector) of Q39 and isolate it from the foil pad. If this restores modulation, it suggests you have voltage on the base leg of Q39 when you shouldn't.

And if isolating the collector of Q39 doesn't help, C153, a 1uf electrolytic is the next suspect that comes to mind. If it fails as an open circuit, mike gain gets clobbered.

73

 

[Handy Andy]

I've got some old stuff but I also wanted to let you know - check for shorts!

The Mic amp pin 3 needs power - it gets that from the 8V feed to the chip.

So make sure you have a "trickle" voltage present to POWER the input of Pin 3 of the 4558 chip it's the Mic amp - if the power supply feed is blown or not working you'd have no audio - it'd act dead - I've seen the Feed resistor R175 and R178 blown on one form or another - cracked - from people trying to extract more out of this little chip.

​

 

[Low_Boy]

Great Andy and Nomad. Some of this I did not know. I fortunately worked the last two days so tomorrow I have some new ammo to go at this with. I will update tomorrow
BIG THANKs.

 

[Low_Boy]

And again Nomad you are the man. First isolated the collector of Q39 no difference and it was getting 8+ volts. I pulled C153 and tested it it was way low. Replaced it and modulation is back. Looking at Andy's schematic I see how that would have a big effect but I may not have no figured that particular cap.
Thanks guys.