Wouxun KG-UV920R finaly here. Maybe.

[VK2AAH]

I used the term "quality" not on the basis of a sample of one, but because these radios require rail voltage to achieve the specified power, and that the modification that THEY recommend results in the radio no longer meeting spec. That to me is the epitomy of poor quality... the radio can't meet spec without having to drive the device to the point of failure- and the manufacturer knows it!!!

Someone asked how the Chinese sell radios much cheaper than the rest and I would think the answer is obvious... they don't waste time on excessive research & development nor do they get all hung up on western notions like quality control...

Cheers

Richard
VK2AAH

[VK2OMD]

For those who own or contemplate buying a KG-UV920P, the driver circuitry has changed from the earlier R model to an earlier P model.

The later P model that I repaired a blow driver FET already had measures to reduce the driver voltage, but the Wouxun factory recommended a mod to further reduce driver voltage.

The root issue for owners / buyers is about a problem known to Wouxun with driver dissipation that causes failure in some radios, and their design changes from the R to two versions of the P model have still not fixed it. Perphaps the 8V mod fixes it, time will tell.

If you own one, you could ignore all this, you could do the mod as currently described (at the risk of messing something up), or you could wait and fix a bigger problem IF it occurs. If you restict cooling air to the bottom (eg put it on the floor under a car seat, and that is NOT what happened in this case), then a problem is more likely to occur, and sooner rather than later.

My guess is that replacement of a damaged driver FET and performing the 8V mod would be a minimum of 1hr work for someone who had done the job before, probably 1.5hr, so your expected cost of commercial repair might be $120 + shipping... which takes you into the $170 region for repair to a $300 radio... something to avoid!

If you bought the thing in Australia and it fails and you claim during warranty, then your costs will be lower. If it fails later, see above.

Owen

[VK4GHZ]

The ONE bit of information that NEEDS to be shared here is the service manual, and Wouxun seems determined to keep that confidential...

A search reveals this:
http://cbradio.com.ua/showthread.php/79 ... n-KG-UV920
Click on the obvious in the first post.

The documentation fails to provide any version information!
Whilst there is a lot similarity between the PCB overlays and the pictures posted on vk1od.net, I suspect this document may relate to the R version.

Whilst it does not meet Icom (etc) documentation standards, in the absence of anything else, it's a good start, if any 920R/P owner is looking for some documentation.

[VK2OMD]

...
Whilst there is a lot similarity between the PCB overlays and the pictures posted on vk1od.net, I suspect this document may relate to the R version.

I think that is the R version from pics I have seen of R and P.

The schematic you referenced shows a RD07 driver and 2SK3476 pre-driver, the later model P that I repaired used only one stage, a 2SK3476 driver and quite different layout.

I showed a pic of an early P model in my article, clipped from http://hamgear.files.wordpress.com/2012 ... inside.jpg . Looking at the bigger pic, it can be seen to use a RD07 driver and no pre-driver. The later P model used a 2SK3476 driver with the SS saddle over it. God knows what is being made this month!

Owen

[VK4GHZ]

Courtesy of Mark, VK5QI, these are the thermal images of the KG-UV920P RF driver transistor you may have seen before, albeit briefly.
Note cursor location is on the driver transistor.

RF driver - taken upon key-up
(courtesy VK5QI)

IR_0179.jpg (71.42 KiB) Viewed 5667 times

RF driver - taken 5 seconds after key-up
(courtesy VK5QI)

IR_0182.jpg (74.87 KiB) Viewed 5667 times

In correspondence today, Mark writes

I ended up replacing the driver FET (which was fairly annoying, but doable with the right tools). I haven't modified the driver fet's supply down to 8v yet.

Mark will be blogging about the FET replacement and mod soon, and a link will be provided once this is published.

Images re-posted to encourage all KG-UV920P owners to diffuse a potentially ticking time bomb!

[VK5QI]

Aaaaand here's the relevant blog post: http://rfhead.net/?p=539

Spelling/Grammar corrections appreciated.

- Mark

[VK3DXE]

Just to add to the knowledge base, I performed the "8V mod" on my 920P a couple of months back in the hope that it would prevent any further TX issues with the radio. Unfortunately this was not the case though, as it recently popped it again. I have been very concious of keeping overs very short, but a combination of a very hot Melbourne Summer evening and a 1.5 minute over at high power on UHF saw my output suddenly drop to zero.

For the record, I measured the radio's output at various frequencies (bottom, middle and top of both 2m and 70cm bands at low, medium and high power settings) into a dummy load and found almost negligable difference in output before and after the mod.

I found an email address for Wouxun and emailed them, but experienced that very Chinese "reluctance to admit anything that may in the least indicate acceptance of responsibility". So, the next step is to order a replacement FET off ALIEXPRESS or eBay and attempt the repair myself with my very limited workshop facilities. If possible, I'll try to document each step in order to assist others who find themsleves with an otherwise useless radio.

[VA3KPP]

Does anyone have a good set of instructions and pictures for this mod?
My 920P has been dead for a year and I'd love to repair it if possible but the images and instrcutions I have from Wouxun make it hard to determine exaxtly what needs to be done.

[VK3DXE]

Time to pull my finger out and do this repair.

OK1DX has a nice solution for those wishing to replace the driver FET at home: http://ok1dx.cz/constructions/uv920p/uv920p.html

Note that what's underneath the board may vary depending on the version of the radio, but the screwed-down extra heatsinking across the top of the device should hopefully keep things cool enough to avoid any further failures.

I've ordered some 0.8mm copper from Hearns Hobbies that should arrive with some spares for my new quad copter next week some time, so will get to work on it then.