Two VX-3000Us, RX fine but 'burp' and cut out on TX

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oz_com
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Joined: Mon Aug 18, 2008 2:12 pm

Two VX-3000Us, RX fine but 'burp' and cut out on TX

Post by oz_com » Mon Aug 18, 2008 2:37 pm

A few months ago, I bought a couple of VX-3000U's from a large lot on eBay. At the time, I tested them for RX/TX, then put them away until I would have time to play with them.

Now I am finding that receive and tone decode is fine, but they do not transmit, though I remember they did earlier. When I key up, the speaker makes a little 'burping' sound. RF output on the wattmeter is around 1 watt, and the needle shakes in little spurts. I don't have access to a service monitor, but there is no modulation on frequency that can be picked up with another radio.

At one point, on the low-power (5W) setting I had it putting out maybe 2 watts with audio for just a second, then it would drop out. The way it drops out and burps reminds me a lot of a handheld with a battery going dead. However, with a 13.2 VDC power supply connected, the voltage across the leads never drops below 12.9 VDC while the radio is keyed. I can't smell any smoke anywhere, and nothing seems to be getting "hot."

Both radios do this. I swapped out their mikes, and switched their cords end-to-end, and tried each on different power supplies. If I power up the radio with the "monitor" button pressed, there is a beep and if I key up right then, it puts out about 25 Watts for about 1 second. Then there are four beeps and there is no more RF output. I have no idea what power-up with monitor engaged is supposed to do; I'm just grabbing at straws here since I have no programming manual.

The code plugs seem to upload and download just fine using the CE19 software under MS-DOS 5 environment on a 486 machine, plenty slow at 25 MHz. If I had one radio, I'd straight out assume I just have a lemon - bad power supply, or maybe a bad mic. But two radios from the same lot?

The only other thing these radios have in common is that they both were programmed by the seller before shipping. I played with the software, eliminating the Time-Out Timer and reducing the penalty timer from 50s to 5s, but no change.

Can anyone say this resembles a symptom that's been seen on this kind of radio? Or, can you tell me if there are any programming "tricks" and "traps" that must be remembered when programming these radios? I have no sample default programming file to compare with my radios.

Thanks for your attention and your suggestions,

-T.

oz_com
Posts: 6
Joined: Mon Aug 18, 2008 2:12 pm

More symptoms

Post by oz_com » Mon Aug 18, 2008 10:10 pm

OK, so when I got home I just had to play with it, and found something even more interesting.

Once again I keyed up on low power and it sputtered, rapid fire like tat-tat-tat-tat.

Then I realized the noise was also coming from the next room. I looked over and the TV was going nuts, with full screen and audio interference. Since the radio is nowhere near where the 75-ohm TV cable runs, I thought this stuttering must have some serious power to it.

Plus, I could feel an old-fashioned RF buzz coming on.

So I got out my field strength meter and boy, does the needle ever swing when the radio is sputtering.

I don't have a frequency counter and instead use my Uniden BC-92 scanner, which can almost instantly lock on within a few KHz of a carrier. Although it could not identify the frequency, it too would amplify the sputtering noise through its speaker.

This is just getting worse and worse isn't it? :-) Anyone want to venture a guess as to what's fried on my rig?

Thanks,

-T.

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KF4SQB
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Location: Moultrie GA

Re: Two VX-3000Us, RX fine but 'burp' and cut out on TX

Post by KF4SQB » Thu Aug 21, 2008 3:56 pm

Does this radio have it's coax connector "hard-mounted" to the chassis, or on a short coax pigtail? If on a coax pigtail, check the ground of the pigtail. I've had similar problems to yours (but not exact) from that before.
Brett Kitchens
KF4SQB

kf4sqb "at" wetsnet "dot" com

Of all the things I've lost, it's my mind I miss the most.......

oz_com
Posts: 6
Joined: Mon Aug 18, 2008 2:12 pm

Re: Two VX-3000Us, RX fine but 'burp' and cut out on TX

Post by oz_com » Thu Aug 21, 2008 11:34 pm

I got it working. It was a bad connector. Actually, two bad connectors - one on the power supply, one in the car. With both radios acting the same way, I knew it had to be something simple.

The fact it didn't work on the wire currently powering my Motorola SM-50 (which has always worked) threw me for a bit there. That wire must have some resistance or a poor ground that I wasn't aware of. I guess the SM-50 must be more tolerant of the voltage drop.

As far as the voltmeter showing adequate voltage across the leads... I need to remind myself that digital voltmeters, even with auto-range defeated, are not fully responsive to transient changes.

By the way, the VX-3000 does have a pigtail terminated in a SO-239. I'll take your suggestion and keep a close eye on it.

Mind you, I'll still take the pigtail over the crazy little mini-UHF plug that /\/\ puts on its stuff... any day!

-T.

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KF4SQB
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Location: Moultrie GA

Re: Two VX-3000Us, RX fine but 'burp' and cut out on TX

Post by KF4SQB » Fri Aug 22, 2008 10:22 am

oz_com wrote:Mind you, I'll still take the pigtail over the crazy little mini-UHF plug that /\/\ puts on its stuff... any day!
Agreed! I don't know how common the problem I had actually is. It was with a Yaesu FT-212RH 2m FM rig. The center conductor of the coax pigtail was soldered, but the shield was only connected via a mechanical clamp, which also happened to be what secured the pigtail inside the radio. Over time, the screws in the clamp loosened up a little, and I started getting intermittent problems. I tightened the screws back up, then soldered the coax shield to the clamp, and the clamp to the chassis. Problem solved!

BTW, glad to see you got it figured out and working 8) .
Brett Kitchens
KF4SQB

kf4sqb "at" wetsnet "dot" com

Of all the things I've lost, it's my mind I miss the most.......

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