Rci 2995dx no tx

[thumper937]

I've got a 2995dx has no tx output rx works fine I also unhooked the amp board completely to rule.that out and hook coax from.s0239 directly to main board. I can't find any voltage info on this radio and the schematic on cb tricks uses bipolar finals so I would assume voltages would be different of there are any on that schematic. here are some voltahes i took.

Rx. Tx
Driver irf520
G.02. 3.71
D 7.72. .08?
S 0. 0
QUESTION MARK ON TX BECAUSE M.M. WON'T STBLEIZE ON THAT PIN MAKES A WEIRD NOISE

FINAL Irf520
G .07. 3.95
D 7.72 7.74
S 0 0

Voltage regulator B827
B 13.12. 12.99
C 7.72. 7.65
E 13.67. 13.66

 

[thumper937]

Even if bias wasn't right I should still have some watts comming out of the radio

 

[nomadradio]

The DC-voltage readings look about right.

First thing to try is to unplug the amplifier-keying plug just to the front of the driver transistor. It's a small plug with two wires, usually brown and black.

If the amplifier has died, you'll get barefoot power once the amplifier's keying wire is unplugged.

73

 

[thumper937]

The DC-voltage readings look about right.

First thing to try is to unplug the amplifier-keying plug just to the front of the driver transistor. It's a small plug with two wires, usually brown and black.

If the amplifier has died, you'll get barefoot power once the amplifier's keying wire is unplugged.

73

The amp is completely unhooked from the radio that's one of the first things I did just in case there was a problem with the amp that would cause it not to let the tx power past the amp.

 

[nomadradio]

Do you have a second radio you can set to the same frequency as the RCI?

Plug a coax jumper into it. The exposed center pin at the far end of the jumper becomes a half-inch long "sniffing" antenna.

If the second radio hears nothing, poke the end of the jumper inisde near the radio's transmit circuits. If you still hear nothing, the RCI's power sections are probably not at fault. If the radio isn't generating the transmit signal to begin with, there's nothing to amplify.

If you can hear the RCI transmit in the second radio, at least you know the radio's transmitter is generating a transmit signal.

How did you jumper the radio circuit board directly to the antenna socket? Seems to me you would need something like a tiny barrel connector to fit the tiny coax plugs inside the radio.

73

 

[thumper937]

Do you have a second radio you can set to the same frequency as the RCI?

Plug a coax jumper into it. The exposed center pin at the far end of the jumper becomes a half-inch long "sniffing" antenna.

If the second radio hears nothing, poke the end of the jumper inisde near the radio's transmit circuits. If you still hear nothing, the RCI's power sections are probably not at fault. If the radio isn't generating the transmit signal to begin with, there's nothing to amplify.

If you can hear the RCI transmit in the second radio, at least you know the radio's transmitter is generating a transmit signal.

How did you jumper the radio circuit board directly to the antenna socket? Seems to me you would need something like a tiny barrel connector to fit the tiny coax plugs inside the radio.

73

I pulled the jumper inside the radio going to the so239 and plugged it into the main board completely bypassing the amp board. Factory jumper is now going from main board to s0239. I have the rci going into a bird 43 then into a dummy load I can hear the rci on another radio that's on my bench it has audio buy barely moves the needle on the bird maybe 1/2 watt at the very most.

 

[nomadradio]

Just re-read your first post, and missed a big clue.

The DC voltage at the Drain (center pin) of the driver IRF520 drops to .08 Volts in transmit mode.

That will sure cripple the RF power. This raises suspicion for L29, the RF choke that should be feeding the same DC voltage as the final transistor's center pin to the driver's center pin.

If L29 has become a high resistance, the next question would be "why?". A blown driver transistor could damage L29.

Do you have a way to test a IRF520? Never have figured out a good way to do this with a simple multi meter. We use the cheap Chinabay testers for this.

But that's the next question to answer. Why is there no supply voltage to the driver's Drain terminal in transmit mode?

73

 

[thumper937]

Just re-read your first post, and missed a big clue.

The DC voltage at the Drain (center pin) of the driver IRF520 drops to .08 Volts in transmit mode.

That will sure cripple the RF power. This raises suspicion for L29, the RF choke that should be feeding the same DC voltage as the final transistor's center pin to the driver's center pin.

If L29 has become a high resistance, the next question would be "why?". A blown driver transistor could damage L29.

Do you have a way to test a IRF520? Never have figured out a good way to do this with a simple multi meter. We use the cheap Chinabay testers for this.

But that's the next question to answer. Why is there no supply voltage to the driver's Drain terminal in transmit mode?

73

Someone did replace the driver before I got the radio. I know this because all the other 520s were stamped 520 this one wasn't. I replaced both the driver and final with brand new 520s to rule that out from the start. How can a guy check L29 for resistance?

 

[nomadradio]

Simple way would be to probe each end while in transmit mode. If you have 7 or 8 Volts DC on one end and not on the other, this means L29 is bad.

And if it drops below 1/10 of a Volt on both ends. it's time to look for a damaged foil trace feeding into L29.

73

 

[thumper937]

Okay I probed it while in rx mode I have 7.71v on both ends tx mode I have 7.62v on one end and 0.08v on the other end