When I got back to Arizona after summer escapades, I went to update to my codeplug only to find that my 878 (UVII+) won’t turn on.

Last time I had used it was on a SOTA outing to Stob Ban on the 2nd of August, the radio was inside my bag with a rain cover until I tried to make a contact, I was in cloud but it was not actively raining so should have been well within the IP54 rating.

I tried the key press resets, two different batteries, etc. I tried getting in touch with Anytone to no avail, and Bridgecom said that once they are out of warranty, the radios get replaced as no schematics are supplied to them, and no major parts are available.

So, I took it apart, as any respectable clown would. I found that the seals at the top of the radio were poorly seated, and the main shell has an o-ring between the chassis and the plastic case: not a brilliant design for a good mechanical seal. More of a slip fit than a seal compressed between two flat surfaces.

Inspecting the board I found what looked like a blemished component. I think a small amount of water got in and sat between the display/GPS ribbon and the main board. My guess was that the MOSFET in question is related to switching on power to the unit. The part is a VBsemi AO2301, a part I was only able to find on eBay direct from China. I am not very good with surface mount parts, however after a couple of weeks the part arrived, I swapped it out and the radio powers on again.

When I was reassembling the rig, I found an LDMOS (A5M06) which is the power amp, and had a weak thermal connection to the metal chassis via a spongy thermal pad, which was about 1mm thick. I decided to replace this with a copper pad made from pipe I ground down until it fit perfectly, then added silver heat compound to hold it in place. Maybe this will help with something. I also decided to add some anaerobic gasket material to the seals (automotive) when putting it back together, in a bid to help with the poorly sealing surfaces.

So, if you have an 878 that shows no life when you turn it on, there is a chance that this is the cause. There is a video on youtube showing the procedure to dismantle the radio: nothing particularly difficult, one solder point for the antenna output. Practice SMA work, as I shall do soon.

---

Filed under: default - @ October 1, 2024 4:41 am