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#1
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MFJ-269 repair (I win)
I just repaired an old MFJ-269 antenna analyzer. This time, the 4
diodes around the RF connector were NOT blown. Instead, it was crappy SMT soldering for the components surrounding the diodes. The solder joints looked ok before I resoldered them, but were obviously a bad connection because several resistors just fell off the board when I touched one end with the soldering iron, indicating the other end was not properly soldered. With the resistor removed, the PCB pad looked like it had never been soldered. If you don't have good soldering tools, a steady hand, and a good microscope, DON'T try this as you'll probably make a mess, as I did before I realized what was happening. Because the various parts on the RF board were not originally making good contact to the PCB pads, the calibration is off. The display reads about 12% too high for impedance and dead on for reactance. I'm debating if it's worth calibrating. http://www.w8ji.com/mfj-259b_calibration.htm Now working on an MFJ-259A, which looks like the usual blown diode problem: http://802.11junk.com/jeffl/MFJ-269-repair/ -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#2
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MFJ-269 repair (I win)
On 11/7/2015 8:25 PM, Jeff Liebermann wrote:
I just repaired an old MFJ-269 antenna analyzer. This time, the 4 diodes around the RF connector were NOT blown. Instead, it was crappy SMT soldering for the components surrounding the diodes. The solder joints looked ok before I resoldered them, but were obviously a bad connection because several resistors just fell off the board when I touched one end with the soldering iron, indicating the other end was not properly soldered. With the resistor removed, the PCB pad looked like it had never been soldered. If you don't have good soldering tools, a steady hand, and a good microscope, DON'T try this as you'll probably make a mess, as I did before I realized what was happening. Because the various parts on the RF board were not originally making good contact to the PCB pads, the calibration is off. The display reads about 12% too high for impedance and dead on for reactance. I'm debating if it's worth calibrating. http://www.w8ji.com/mfj-259b_calibration.htm Now working on an MFJ-259A, which looks like the usual blown diode problem: http://802.11junk.com/jeffl/MFJ-269-repair/ That's how I got my MFJ-259B, about 15 years ago, Someone at the local ham club had a defective one, gave it to a fellow ham to fix, he returned it saying that he couldn't fix it. I told the owner, let me have a shot at it, if I can fix it I'll buy it from you. It was "the usual blown diode problem:" I shocked the owner when I gave him $60.00 for the repaired unit. I don't think he expected me to contact him again. Mikek |
#3
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MFJ-269 repair (I win)
On 11/9/2015 11:18 AM, amdx wrote:
On 11/7/2015 8:25 PM, Jeff Liebermann wrote: I just repaired an old MFJ-269 antenna analyzer. This time, the 4 diodes around the RF connector were NOT blown. Instead, it was crappy SMT soldering for the components surrounding the diodes. The solder joints looked ok before I resoldered them, but were obviously a bad connection because several resistors just fell off the board when I touched one end with the soldering iron, indicating the other end was not properly soldered. With the resistor removed, the PCB pad looked like it had never been soldered. If you don't have good soldering tools, a steady hand, and a good microscope, DON'T try this as you'll probably make a mess, as I did before I realized what was happening. Because the various parts on the RF board were not originally making good contact to the PCB pads, the calibration is off. The display reads about 12% too high for impedance and dead on for reactance. I'm debating if it's worth calibrating. http://www.w8ji.com/mfj-259b_calibration.htm Now working on an MFJ-259A, which looks like the usual blown diode problem: http://802.11junk.com/jeffl/MFJ-269-repair/ That's how I got my MFJ-259B, about 15 years ago, Someone at the local ham club had a defective one, gave it to a fellow ham to fix, he returned it saying that he couldn't fix it. I told the owner, let me have a shot at it, if I can fix it I'll buy it from you. It was "the usual blown diode problem:" I shocked the owner when I gave him $60.00 for the repaired unit. I don't think he expected me to contact him again. Mikek Good for you Mike, I once came across an Ameritron ALS-600 with analogue power supply and a couple of vhf-uhf transceivers in a junk box at a garage sale. I asked how much for the whole box. I was told 60 bucks. I assumed the stuff was probably defective. However, the person selling it was a woman who had lost her ham husband. I wrote her a check for $500. That is what I figured a defective ALS-600 might be worth. She was shocked. I did not do this to be generous. I did it because I knew that if I really screwed her on that deal, I would feel guilty every time I used that amplifier. It turned out that the amplifier actually worked but introduced a bit of distortion. I sent it to MFJ and they rebalanced the output transistors. It has very good fidelity now. The trip to MFJ cost about 200 dollars. I had to buy one of their shipping boxes. Those are not cheap. Still, 700 dollars for an ALS-600 is a bargain. I liked that design so well that I bought an ALS-1300 which is just two ALS-600s in a box. So, I have the 600 as a backup amp. That 1300 has been such a good work horse. Tom at MFJ and others who worked on that amp design did a fine job. Originally there was a defect in the switching supply that they bought for it. Mine has been updated to protect the 12 volt supply. |
#4
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MFJ-269 repair (I win)
In article ,
Jeff Liebermann wrote: Now working on an MFJ-259A, which looks like the usual blown diode problem: http://802.11junk.com/jeffl/MFJ-269-repair/ "Of course, when I got it back together (for the 2nd time), I found the reading to be erratic and intermittent. It took a while to discover that the owner had somehow spread the gold center contact leafs in the type-N connector and my adapter wasn't making contact." My repeater cohort and I have seen quite a few N connectors which were damaged in precisely this fashion. One cause: some N-connector adapters floating around out there have center pins which are either too large in diameter, improperly tapered, or which protrude too far "forwards". I suspect that male N connectors, if improperly installed, can have the same problem (the pin is pushed too far into the connector). In either case, (over)tightening such an N-male connector onto an N-female will cause it to make excellent contact... once... as the pin splays the female connector's contacts outwards. Subsequent connection attempts with a properly-configured N male won't make good contact. In a pinch, you can try pinching the contact fingers back in, but it's nigh-on impossible to restore them properly. Better to remove the damaged female connector and replace it. Then, check all of your male N connectors to make sure the center pin has the proper taper and is in the proper position. A center pin with a rounded blunt end (rather than a properly-tapered point) is Trouble. This turned out to be all that was wrong with a defective TK-981 I picked up at the De Anza ham flea market last year. Cut off the N connector, solder-and-crimp a new one onto the pigtail, and it checks out fine. |
#5
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MFJ-269 repair (I win)
Dave Platt wrote:
One cause: some N-connector adapters floating around out there have center pins which are either too large in diameter, improperly tapered, or which protrude too far "forwards". I suspect that male N connectors, if improperly installed, can have the same problem (the pin is pushed too far into the connector). With some types of cable, there is a tendency for the inner conductor to "lengthen" relative to the outer shield when the cable is repeatedly wound and unwound in a small radius. This can sometimes push out the connector pin a little. |
#6
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MFJ-269 repair (I win)
On Mon, 9 Nov 2015 11:18:20 -0600, amdx wrote:
That's how I got my MFJ-259B, about 15 years ago, Someone at the local ham club had a defective one, gave it to a fellow ham to fix, he returned it saying that he couldn't fix it. I told the owner, let me have a shot at it, if I can fix it I'll buy it from you. It was "the usual blown diode problem:" I shocked the owner when I gave him $60.00 for the repaired unit. I don't think he expected me to contact him again. Mikek Yep. I'm working on an MFJ-259B which might have blown diodes. It's very easy to do. I'm considering adding a 1M resistor from the center pin to ground to bleed off any static buildup. Beware of ungrounded antennas. BTW, I paid $100 for mine. Grumble... I'm also working with another ham that has an old MFJ-269 with some very strange problems. I can't conjur a theory except that his has the same problem as mine with the crappy soldering on the RF PCB. I've recommended reflowing all the SMT parts around the coax connector. That should either fix it, or destroy it. Drivel: I'm trying to find a replacement LCD 1602 display with backlighting. Plenty on eBay, but all the wrong size. Argh. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#8
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MFJ-269 repair (I win)
"Dave Platt" wrote in message
... In article , Jeff Liebermann wrote: Now working on an MFJ-259A, which looks like the usual blown diode problem: http://802.11junk.com/jeffl/MFJ-269-repair/ "Of course, when I got it back together (for the 2nd time), I found the reading to be erratic and intermittent. It took a while to discover that the owner had somehow spread the gold center contact leafs in the type-N connector and my adapter wasn't making contact." My repeater cohort and I have seen quite a few N connectors which were damaged in precisely this fashion. The N connector is so-called because there are N different ways to assemble it, and all of them wrong :-) |
#9
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MFJ-269 repair (I win)
On 11/7/2015 8:25 PM, Jeff Liebermann wrote:
I just repaired an old MFJ-269 antenna analyzer. This time, the 4 diodes around the RF connector were NOT blown. Instead, it was crappy SMT soldering for the components surrounding the diodes. The solder joints looked ok before I resoldered them, but were obviously a bad connection because several resistors just fell off the board when I touched one end with the soldering iron, indicating the other end was not properly soldered. With the resistor removed, the PCB pad looked like it had never been soldered. If you don't have good soldering tools, a steady hand, and a good microscope, DON'T try this as you'll probably make a mess, as I did before I realized what was happening. Because the various parts on the RF board were not originally making good contact to the PCB pads, the calibration is off. The display reads about 12% too high for impedance and dead on for reactance. I'm debating if it's worth calibrating. http://www.w8ji.com/mfj-259b_calibration.htm Now working on an MFJ-259A, which looks like the usual blown diode problem: http://802.11junk.com/jeffl/MFJ-269-repair/ I've generally found MFJ stuff has decent design and rather good components, but terrible wave soldering on the PC boards (and sometimes hand soldering on components off the board like chassis mounted connectors). On my 259B, it worked well for almost a year, and then became erratic. When I saw how many soldered joints weren't, I decided not to try to figure out which ones were bad: I just went around and resoldered everything on the board. Since then it has worked perfectly. Wave soldering is a marginal thing, I think it is amazing how many times it does work. Think about how it goes: Basically the PC board is suspended just above a vat of molten solder, and a wave is caused to run across the vat. The wave, we hope, just reaches up to the connections on the board and solders them. Too high and it makes solder bridges. Too low and it either misses connections or at least does not stay on them long enough. And it is not long on a connection at best, so does it get it hot enough? It is not just fairly inexpensive things like my MFJ analyzer that have had problems. I did the "resolder the whole board" thing on my Phase Linear preamp many years ago also, and that was by no means low end! Bob Wilson |
#10
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MFJ-269 repair (I win)
I have a number of MFJ items that I picked up in non-working
conditions and fixed up. They include MFJ-259B, MFJ-931, MFJ-949E and others. Other than the 259B which involved cleaning leaky battery residue and replacing the input diodes. most of the work involved resoldering and/or replacing blown meters, and in once case a bandswitch. Once repaired, everything has remained totally reliable and functional. I've never had problems ordering parts from them to fix the stuff. The 'Mighty Fine Junk' reputation is deserved only because of the poor soldering, but once repaired it serves one well -- at least in my books! Irv VE6BP |
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