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Thread: XTL2500 Died in Transit

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    Default XTL2500 Died in Transit

    Hi all

    Wondering if anyone has ever seen a problem like this before.

    I sold an XTL2500 a few weeks ago, and when the seller got it he reported no power output. I made sure he had the correct setup, and after verifying that he hadn't just accidentally killed the PA by TXing into an open, I accepted a return to take a look at the radio.

    When I got it back, it is indeed putting out no power on TX. Ref Osc is dead-on as it was when I sent it out, but I'm getting about 1mW of power out of the antenna port which would imply that the PA is dead.

    I've got a claim with USPS to reimburse the radio since I'm guessing it somehow got damaged during shipping (even though it was padded to all hell in the box). I'm just curious if anyone else has ever seen a 2500's PA die for seemingly no reason.

    Radio was at full TX power before I packed it up, seller gets it, no power out. Super frustrating to deal with.

    Cheers!


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    Static discharge into the antenna connector as a result of the shipping, rubbing, dragging etc.?

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    Quote Originally Posted by wiredwrx View Post
    Static discharge into the antenna connector as a result of the shipping, rubbing, dragging etc.?
    I vaguely recall there being an FSB about this.

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    Was the radio wrapped in regular bubble wrap? I bought a load of Systems Sabers packed like that and found a bunch with odd failures.

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    It was packed with just standard bubble wrap - I never even considered that ESD would be an issue on a fully-sealed radio. That could definitely be a possibility. I don't think I've ever shipped out or received a radio in anything other than standard bubble wrap so I must've been extremely unlucky this go-around if that's the case.

    From the other thread on here about the XTL5000 PA, I'm guessing that I'm SOL for getting a replacement chip too.

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    Its just bad coincidence. No ESD.

    HPM could do it, but not ESD.

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    I have one that suffered the same issue. Boxed up and shipped working 100%. When I got it: driver power only (high power deck so 20ish watts out). Think the PAs flopped.

    Also have a mid power XTL5000 that is doing exactly your issue as well down to power reading. I thought it was the "antenna switch" but never dug into it.

    Definitely interested to know if I can get either back to life on the bench. I have been hesitant to toss them in a dumpster.

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    "me too". Have an MP VHF that worked before being put into dry storage (my closet). Took it out, powered it up, almost zero power out. No programming was changed. It just lost it's voice. Like a cheerleader without her megaphone. Puts out a few mW (enough to be heard on a portable nearby) but nothing more.
    Your streaming makes me AES-256. Keep it up and you'll soon have nothing to listen to.

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    The even more interesting thing is that this radio was my daily driver for nearly 3 years - and it took plenty of abuse. From 110F down to -30F over the years installed in my vehicle and it never complained.

    I guess it just didn't want to leave.

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    Must be how Motorola does their accelerated life testing.

    3 days with USPS is equivalent to 3 years in your car.

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    X-ray does something? I've had things go fucky before at airport after they out it through the machine. Induced energy? Guessing.

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    Ive found in the couple times i've sold someone a radio (not always Moto), it really helps to wrap them in an ESD bag first (the metalized Mylar not the pink ones) and that'll really help with any ESD from packing peanuts.

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    Quote Originally Posted by Mars View Post
    X-ray does something? I've had things go fucky before at airport after they out it through the machine. Induced energy? Guessing.
    You may be on to something here ... Do these failures only happen after the radios have been shipped by air? A couple of years ago marks the implementation of the latest generation of "x-ray" scanners. These are ones to replace the former bunch that use to wipe out unexposed camera film. I wonder if something in the finals reacts to the radiation kind of like EMP? Maybe a good test would be to take an unwanted-but-known-working radio down to UPS and have them run it through their parcel scanner a couple of times.

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    Quote Originally Posted by PossumCop View Post
    You may be on to something here ... Do these failures only happen after the radios have been shipped by air? A couple of years ago marks the implementation of the latest generation of "x-ray" scanners. These are ones to replace the former bunch that use to wipe out unexposed camera film. I wonder if something in the finals reacts to the radiation kind of like EMP? Maybe a good test would be to take an unwanted-but-known-working radio down to UPS and have them run it through their parcel scanner a couple of times.
    I can't imagine the radiation from a single X-ray machine would be able to induce enough damage, especially through an aluminum chassis. Maybe I'm wrong, who knows?

    Regardless if I've got time in the next few weeks I might crack the unit open for some troubleshooting. Buyer got his money back but I'd really like to not be out a few hundred bucks.

    Looks like the PA FET is a somewhat standard package. The OEM amplifier is NLA but it might be possible to bodge in a new aftermarket one with a little fussing around.

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    Probably shock and vibration. Nothing to do with shipping by air or X-rays, just shipping in general.

    The radio has a latent mechanical weakness somewhere that never presented itself while the radio was sitting on your desk or crusing up and down the freeway in your vehicle. But after being kicked around a bit by USPS, it finally breaks.

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    Quote Originally Posted by axel View Post
    Looks like the PA FET is a somewhat standard package. The OEM amplifier is NLA but it might be possible to bodge in a new aftermarket one with a little fussing around.
    I'd definitely be interested to know. If we can reverse engineer a working FET to find it's bias range and such it shouldn't be too difficult... But I don't have one to spare to do myself.

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    Did some more digging this weekend since I'm not busy. Busted out the service manual and started probing. Right now, initial testing is getting somewhere.

    I've been going down the TX power troubleshooting chart and found what could be a smoking gun. TP0958 reads 4.35V when I'm in TX mode. According to the troubleshooting flowchart, it needs to be >4.5V. Interesting failure, and could be a red herring, but it's somewhere to start.

    txpwr-chart.PNG

    Sadly, as expected, U3550 is proving difficult to identify. The Motorola P/N is 5185130C65, which comes up as NLA pretty much everywhere I've checked. However, as luck would have it it's not a Motorola custom IC.

    u3550-circuit.jpg

    As far as I can tell, that's the old Freescale logo on the chip, but H015MUZ doesn't yield me any results on google. It looks like it's some kind of RF pre-amp, and the DSM calls it "VHF/UHF/800 MHZ LDM" which I'm guessing stands for "LDMOS."

    u3550.PNG

    Anyone who has any ideas, feel free to throw them out there. I'll probably ask around a couple electronics forums to see if anyone can help in the search.

    EDIT

    Oh yeah, and as a bonus, for anyone looking for a replacement P/N for the VHF main PA FET, it's an NXP/Freescale MRF1550FNT1. It's EOL from NXP but you can find it for $35 in qty 1 from a couple distributors.

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    That is such a small voltage error. What happens if you follow the tree to YES and measure RF level at pin 16 of U3550?

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    Quote Originally Posted by RFI-EMI-GUY View Post
    That is such a small voltage error. What happens if you follow the tree to YES and measure RF level at pin 16 of U3550?
    That was another suspicion of mine, because you're right that 4.3V is almost 4.5V. I don't own a high-impedance RF probe so I can't easily get an accurate measurement at that pin. It's definitely next on the list of things to check out though.

    The radio does draw the expected current when it's put into TX mode though. That makes me think that it's not the main PA FET that's bad, and that it's just something further up the drive chain that's died and is blocking the TX signal. Another thing pointing to your suggestion I suppose.

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    Quote Originally Posted by axel View Post
    That was another suspicion of mine, because you're right that 4.3V is almost 4.5V. I don't own a high-impedance RF probe so I can't easily get an accurate measurement at that pin. It's definitely next on the list of things to check out though.

    The radio does draw the expected current when it's put into TX mode though. That makes me think that it's not the main PA FET that's bad, and that it's just something further up the drive chain that's died and is blocking the TX signal. Another thing pointing to your suggestion I suppose.
    Whats the rx sensitivity? Many times when the pin diode in the front end goes bad in an antenna switch it will have poorer than normal rf sensitivity.. Normal tx current says the pa device is ok and your problem is further down. Could you have sheared the mini uhf connector center pin off the board???

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    I'll have to check that. Good call. You're right that if I'm drawing full TX current that means the FET is getting at least some signal. Bias current alone would not be pulling 5A from the power supply.

    It would be nice if it was something as simple as the PIN diode. I'll see about checking that this evening when I get home.