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Almost FUBAR

Posted 05-15-2009 at 09:17 AM by skigolfmike

I really managed to almost screw up my DX7. I decided to put in the Dimension Engineering Voltage Regulator to improve battery life. Plus I was thinking of getting a TX Lipo to go with it so I really didn't have to think about charging. Just go fly.

I got out the instructions from Dimension and started to work. I thought I got the first lead (Vout) unsoldered, so I went to bend it away from the pad. Unfortunately, it was still soldered to the pad and I pulled the pad off the board. What the @#$%^# do I do now?

Well, I managed to unsolder the other 2 legs from the pads without incident, then it was a matter of unsoldering the transistor heat sink from the board. I quickly found out my 50W iron wasn't going to cut it so I got out the 90 with the big tip. That worked great, except the transistor fell off the board and into a wiring loom where it melted the insulation and stuck.

Needless to say, I was pretty upset with myself for being such an idiot. This was not one of my better days. Time to think of contingency plans. The LHS was still open and if I hurried I could just get there before they closed. Actually, I made it with a minute to spare. Wasn't sure what the plan was, but I could at least think of options.

My first thought was to get a new radio. However, if I did that, I figured I should upgrade in the process. Of the compatible radios they had in stock, they had an airplane 9303 and a heli DX7. Not what I was looking for, so I decided to pass. However, they could get me a radio by Friday, so I at least had options. Also, there is another LHS in town, so it was possible that they might have something in stock too. I was also considering that there was a slim chance I could still fix the radio.

I headed back home empty handed, but I at least had a plan. First thing was to see if I could get the radio turned on to get the data from the menus. Fortunately, I could, so that took a load off my mind. I ended up putting the data from all 5 helis on the DX7 into a spreadsheet so I could setup a new radio quickly. I also did some searches for a DX7se and a 9303 to get some pricing and availability info. I actually found a great price on a 9303 at HeliProz. I wanted the TX by Friday, so the shipping charges to do that would have been prohibitive. Still - it was an option. DX7ses were all $320 everywhere I looked.

Yesterday morning the first call I made was to Tony Stillman at Radio South. I've known Tony for a long time. I flew pattern all through the 90s and went to the Nats every year, so why not give Tony a call and get some advice from an expert. Tony explained all was not lost and that I could solder a jumper from the Vout lead to the + side of the capacitor right below it. He said that should fix it. When I got home later I'd have to try it. He also said I could use electrical tape on the melted insulation on the one lead where the old VR melted it. This was great news; however, I also figured it was not a sure thing. I needed a backup plan.

Fixing my DX7 became plan A. Getting another TX was plan B. I made a call to the other LHS as soon as they opened and they had a DX7se in stock. So, I headed over at lunch to pick it up. since I have 2 helis with AR7100R receivers, my Trex 600 and 700, I figured I program those helis in and bind the SE to them. Thanks to my spread sheets, I was able to setup the models quickly. When I got home I was able to bind and test hover both models uneventfully.

Then it was off to the my kids band concert for a few hours. I'd try to fix the DX7 when I got home.

Basically, I followed the directions except for the Vout lead. I put a pad of hot glue under the Dimension VR so it would stick to the board and to keep it clear of one of the screws that holds the board in place on the TX. Then I made a jumper out of servo wire and soldered it to the plus side of the cap. I reassembled the TX and I did a checkout using my G200. It worked.

Now that I have the DX7se, so I can do this mod all over again. Here's what I learned and what I would do different next time.
  • I would clip the leads from the stock VR with side cutters first, then unsolder.
  • When unsoldering the VR heatsink from the board I would place paper towels in the TX to protect the wiring and catch the hot VR when it comes unsoldered.
That will leave the pads intact and make the job a lot easier.

Use a fine point tip to unsolder the pins and a high wattage iron with a big tip to unsolder the VR heatsink.

I just hope any of you folks planning to make this mod read this first so you don't make the same mistakes I did.

Mike
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