Reddit mentions of Alloet AN8008 True-RMS Digital Multimeter Square Wave Voltage Ammeter MAX Display 9999 Counts Auto/Manual Ranges True RMS

I've had one of these for years and it works pretty well, but it is unnecessarily big and clunky. Personally, I would go with this one instead. I bought it a little over a year ago and it has been a very good meter. I would honestly take it over pretty much any of the Ames meters we sell. If you need one with a current clamp on it, this one will probably do it for you. I don't have one personally, but Big Clive on YouTube does and he seems to like it.

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If you don't already have a meter, don't even bother getting the $4 one. I have a couple that I got with a free coupon and they are all junk. The leads are downright trash. The only time I use one is if I am doing current measurement and I don't want to risk blowing a fuse in one of my good meters.

Remember that you need to mod the radio to bind a FrSky rx, but I can tell you from experience that they work well together.

I hadn't looked at your rx, and I forgot that you're going old school on everything. It's possible that you have a short between those two channels on your FC, which is a problem that's only possible if you have a separate PWM output for each channel, like on that rx. (Pretty much every other way of wiring the FC to the rx only uses one wire.) Do a continuity check between the data pins of those channels on the FC before you spend any money, it could be that simple.

(If you're new to electronics, too, that means use a multimeter to check that the two points are electrically connected. The power and ground pins of each channel should connect to each other, the data pins shouldn't. If your multimeter doesn't have a continuity mode, use resistance mode; if the display shows an absurdly high number, or the same thing it shows when the probes don't touch anything, there's no connection. Also, if this is the case, spend the $20 on a multimeter with an audible continuity test. Most any cheap meter will work for drones, but beeping on continuity is invaluable.

Edit: Some links, sorry they're mobile:

Multi-module for Devo radios, it's a drop in replacement for the stock module, this thread has instructions as I recall. It's an easy mod, mine took about 45 minutes. (Apart from this mod, my Devo 10 is way worse than the Taranis X9D+ SE I replaced it with, btw, so take that as you will.)

A decent $20 multimeter according to EEVBlog, Dave's only real gripe was that it wasn't as good as a $100 meter, for obvious reasons.

For the purpose of testing a fuse any multimeter should work. This is the budget one if like.

I have no clue about that soldering iron you might struggle with it not getting hot enough but should be able to replace a fuse

https://www.amazon.com/Alloet-True-RMS-Digital-Multimeter-Voltage/dp/B072JMBLJS/ref=mp_s_a_1_3?ie=UTF8&qid=1549849481&sr=8-3&pi=AC_SX236_SY340_FMwebp_QL65&keywords=multimeter+aneng&dpPl=1&dpID=41EJHj41StL&ref=plSrch