HW issue with my radio - NOT receiving on VHF.

[LZ2PAJ]

Hi guys,

I need a help with my radio and any advise will be appreciated.

I recently found out that my Retevis is almost deaf on VHF. I wrote almost, because it is only receiving if I transmit on, let's say 145.000mhz with another transceiver, but only from short distances, no more than few meters. This is the only fault, all other functions are working properly. It transceivers with few watts on 2m as always, and it is receiving and transmitting without an issue on UHF.

I do not hear any signal from the local repeaters and HAMS, but they reported to hear me as always.

Spent some time researching for similar reports in the net, unsuccessfully.

73.

Picture of radio board:
https://photos.app.goo.gl/Mcx6b39oenwqGeDh7

[VK3KYY]

Probably something in the VHF preamp is no longer working.

Unfortunately, we don't have a schematic for the UV380 / RT3S

[Pu8ypf]

Estou com esse mesmo problema. O rádio não funciona o VHF.

[N1LSJ]

That's unfortunate - especially as you live so far away. I wouldn't mind having a spare UHF-only one if anyone can get it to me for $40 shipped .

[LZ2PAJ]

Estou com esse mesmo problema. O rádio não funciona o VHF.

It's not easy to determine where the issue is without schematics, however, I think that the problem might be in the preamp VHF transistor. Unfortunately, the transistor that is used by Retevis is unknown, but I think it should be similar or the same as 3SK294 in SOT-343. I ordered and waiting for the delivery... will let you know when I get it replaced.

[DD5XL]

I wouldn't focus on the preamp transistor only:

I had a similar issue at a radio of another club member: He managed to kill one of the PIN diodes in the RX frontend, it was shorted to RF ground permanently.
He played around with a second radio, full 5W power close to the antenna, from then the first one remained deaf.

I've checked the components starting from the antenna socket and found a PIN diode shorted. First check after replacement with a (bigger) BA682 showed normal sensitivity again.
Finally I've ordered some KEC KDS114E PIN diodes which perfectly fits on the footprint and the device was working as expected again.

73 de Bert, DD5XL

[Pu8ypf]

OK friends. Any information about this problem please share here 73

[W4TAB]

I am having a similar issue with my RT3s. It is almost deaf on VHF, I tried older codeplugs and even on the spectrum scope there is nothing showing...

[VK3KYY]

I am having a similar issue with my RT3s. It is almost deaf on VHF, I tried older codeplugs and even on the spectrum scope there is nothing showing...

Does it work when using the official firmware ??

How old is the radio ? i.e is it brand new and potentially may have different hardware to previous versions

[EA4FYM]

Hello, the same thing happened to me on two DM-5R units, but in UHF. I think the origin may be in static electricity, since I use the dual-band antenna to use it in the car.

I started searching on the internet and found the closest thing to the diagram of the Baofeng UV-5R (DM-5R, I didn't find anything). To open the reception it uses two R25 SMD transistors. One for UHF and the other for VHF.

Since the two transistors were the same, I swapped them and now I hear UHF perfectly but not VHF, so I think I have found the solution. I have ordered spare parts for the NPN 2sc3356-25R in SOT-23 package

I Share the pics when i swaps the transistors working in UHF but not in VHF, and testing the oscilating voltages in a power suply..

https://1drv.ms/i/s!Avy5mJCiqq2unVokWb7 ... L?e=0nrKlI
https://1drv.ms/i/s!Avy5mJCiqq2unVkNiBk ... M?e=kJ3Mxy
https://1drv.ms/i/s!Avy5mJCiqq2unVxPuHe ... n?e=dRMRLY

Gretting 73's