Watson W-25AM on the fritz (again)

[timbo]

Had this power supply from new ( 'bout 8 years ) First went wrong just after the 12month mark ( what a surprise ! ) where the voltage would not turn down, would stay at 12v or above , no problem really , as I only ever used it at 13.8v. Lately , though, the voltage is refusing to turn UP, will go down to 2.5v but no higher then 11.5v ( the 13.8 notch is reading 10.7v ) all measured with external voltmeter. I'm guessing Voltage Regulator problem, but never heard of a fault going into reverse before. Anybody else had issues with this, you pay for what you get, Watson PSU ?

[George EI7KO]

The variable power pot on these is notiourious for going bad. I'd be having a gawk at that first...

[timbo]

Looks to be the case here. Took the voltage control out of the circuit altogether and shorted the posts on the PCB, giving max voltage. Was then able to adjust the boards internal VR down to 13.8v. Seems to be quite stable so far.

[Anthony123]

Pointless really having a variable supply to run a radio...I would do away with the Variable control...Set it for 13.8 volts ...Oh and while your at it....Add a over voltage circuit...It can save a hefty repair bill and lots of smoke from your radio....You can add it quite cheaply..

[bigpimp347]

Here's a twist on a six year old thread..

got a crappy W-25AM here for repair..
only goes up to 7.5v but goes down to zero..
transistors are all showing 24v in and 7v out.
there is no internal output adjustment.
so i suppose it's lost half it's output ??
but any ideas where ??

[Mikel]

The front panel variable power went crazy on mine a few years back and i also disconnected it and set the internal pot to 13.8V.

The front panel pot was not totally dead though so I connected the fan directly to the 13.8V and wired the fan through the pot with a resistor I found in my junk box, this way I can vary the speed of the fan or turn it off completely, handy because the fan was far too noisy for my liking.

Also I have the lid unscrewed and have placed a couple of pieces of timber across the top under the lid to increase natural airflow. This way I rarely have the fan running apart from on hot summer days with long overs.

I have uploaded some circuit diagrams that may be helpful for someone but they are of the W-30AM, but obviously there will be many similarities to the W-25 and found them useful when messing about with a fan control.

W_30_AM_Control_board.jpg

W_30_AM_Chassis_mounted_parts.jpg

W_30_AM.jpg

[Mikel]

Here is a fan mod that I found online as well that may be useful. I didn't follow this myself as my simpler manual control mod that I mentioned previously suited my needs but some may find it useful.

W_30_AM_Fan_Controller_mods.jpg

[DX-Digger]

Strange this post should come up, I have just this week had to replace my fan as on a long hi power over the psu thermally tripped out.
Seems the phospherous bearing had siezed.
So I fitted a new one. however i did manage to strip the original fan and unsieze and lubricate and polish the shaft.
So will keep the old one just for emergency spare unit.

[Mikel]

I much prefer a good old fashioned linear power supply for radio use. In addition to the Watson I have a few of the old Maplins linear supplies of various ratings and these are as old as the hills as well and get a bit hot if you push them due to the lack of fans.

The Maplin supplies look identical internally to the Watson in terms of types of transformers, component makes and board colour and construction etc, maybe they came out of the same factory in the far east?

A good tip if you buy a new supply is to check the voltage out with a multimeter before connecting your pride and joy up to it, as the Maplin XM19V 13.8V that I bought in the early 2000's was putting out just over 15V out of the box!

Easy enough to take the lid off and turn it down a bit, but good thing I checked as some things may not like the extra volts.

Getting back to the Watson W-25AM, I also fitted some blue led's to the top of the meters internally to illuminate them. Looks a bit poncey but matches all the other led backlight mods I have done on various other meters in the shack, some blue, some green and some orange.

Incidentally bought my Watson from the 'Triple C' radio shop in Bedwas that many from this part of the world will remember as a great local CB shop and meeting place that sadly closed a number of years ago.

[g1ezj1701+]

For anyone who has a problem with a worn potentiometer,i did try to get a pot with center deten(stop) but no luck but it can be replaced with a 10K anti-log potpotentiometer,i just use a rubber tap washer behind the knob to stop it moving.this is good for the WATSON W-25AM AND THE W-30AM(lucky enough to own both) .
thought it might be of use.