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Uniden Washington (MB8719)


This is about the transmit side only, right?

Have you tried sideband?

A fault on AM only suggests one kind of problem. Low power on AM and SSB both points to the driver, final or a failure upstream from the driver that has reduced its drive level.


Kinda hard to test a weak final without some sort of transistor tester. A dead one can be confirmed with a meter that has a "diode test" feature. But not a weak one.

A "weak" 2SC1969 is a bit rare. Is this a Taiwan or a Phillippines radio?

73
 
This is about the transmit side only, right?

Have you tried sideband?

A fault on AM only suggests one kind of problem. Low power on AM and SSB both points to the driver, final or a failure upstream from the driver that has reduced its drive level.


Kinda hard to test a weak final without some sort of transistor tester. A dead one can be confirmed with a meter that has a "diode test" feature. But not a weak one.

A "weak" 2SC1969 is a bit rare. Is this a Taiwan or a Phillippines radio?

73
ssb does the same.
 
is this low receive and transmit in all modes. if so you may have a problem around the audio IC. sure could use more detailed info as to the problem. was it like this before you changed out all the caps. what PLL is in the radio.
 
well part of the questions answered. did the radio TX fine before the cap change?
same on both AM and SSB?
if both AM and SSB have low TX audio and power, have you verified the mic is good.
if it was fine before the cap change make sure you did not slop solder on one of the joints or put a cap in backwards.
have you verified with a freq counter it TX and rx on the proper channels? I had one a while back that was way off freq and acted some what like yours. it looked like it was RXing and it was way off where it was suppose to be.
 
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Getting the sequence of events right plays a really BIG part in making sense of a circuit fault.

If it was transmitting with full power before the caps got replaced, this is a REALLY STRONG suggestion that somewhere in all the steps to replace all those caps that some part of the process went wrong.

If it worked okay before, and hasn't worked right since the caps were replaced, this invokes a principle called "Occam's Razor".

In a nutshell, it states that all other things being equal, the simplest explanation is usually the correct one.

I would start with a REALLY bright light source and a magnifier. I suspect that there is a solder bridge between adjacent foil pads that occurred while replacing one or more of all those caps.

Considering how many times I have heard "The meter on my RCI pegs out on transmit now. All I did was turn up the audio". Always turns out to be a solder bridge. The AMC transistor he removed is along side a trace to the transmit-side meter circuit.

Or, you could trace the transmit signal through the radio stage by stage with a 'scope. I have found more than one solder fault this way, too.

73
 
glad you found the problem. these old radios are bad about bad solder joints. the last few guy's have had a problem like this was either poor solder joints or solder smeared between two traces. like Nomad stated in his last post a good set of glasses helps a lot. since I have gotten older I have bought a small scope for checking traces with. hook it to my laptop then scan over the joints to see what ones are bad. if you watch on ebay they will have one cheap that will blow up the joints very large and you can see every thing about 25 times its normal size. I paid about 10.00 for the one I have and it has paid for its self more than once. I will see if I can find one and post it here for you so you will know what to get.
 
here is an example of what I am talking about. you scan it across the traces and the picture will show up on the screen of the laptop. they have a light on the end where you put it on the board traces. they come with a stand for the scope end. but after you use it a few times you can just frre hand it so it will focus in on the location you point it at. this is just the 1st version I came across. just scroll through the pages until you find one you think you want to use. you can do a search on you tube and find where some one has it hooked up and see how it works.

http://www.ebay.com/itm/Protable-50...hash=item46641c74b4:m:mM5QZ0G8INTVTeX-iCiMVGQ
 

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