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Uniden Washingto no Recieve

WR989_Dan

Member
Jul 23, 2011
39
3
18
Beer Capital Milwaukee Wi
Hello all have a uniden washington im playing with has great transmit but no recieve tried external speaker nothing meter does not move as it is not picking up anything from the antenna maybe the caps are bad? pll is 8719
 

dan, just a few questions to narrow things down a bit.

when you say the radio has great transmit, what exactly does that mean?

do you have an external wattmeter to verify that the radio is putting out wattage on AM deadkey, and swinging upward with AM modulation?

again using the external wattmeter, does the meter swing upwards with SSB modulation?

try a quick test on the receiver. touch pin 4 of the audio chip with your finger with the radio on and the volume set at a normal listening level. squelch all the way down (counterclockwise).

do you hear a hum from the speaker?

the audio chip is a 10 pin SIP (single inline package) IC chip that is mounted on the right hand side of the PC board and attached to the vertical aluminum wall.
(this is with the front of the radio facing you looking down at the component side of the PC board)

do not mistake the audio chip for the voltage regulator which only has 8 pins, and is mounted to the same aluminum wall.

the audio chip is the one closer to the back of the radio. pin 1 is the closest to the front, and pin 10 is closest to the back.

describe the answers to my questions with as much detail as possible.
the more specific you can be about the problem, the better our chances are of helping you.

LC
 
Ok so yes i have external power on my external wattmeter it shows am deadkey and swing i hooked headphones to external speaker and can here myself plain as day with nice audio ssb does modulate as you talk As for the audio chip when i do touch pin 4 i do here a loud hum in the speaker any more questions i will be happy to answer thanks for the help ill be awaiting your instruction
 
im thinking that when you said this, "i hooked headphones to external speaker and can here myself plain as day". that you meant the PA speaker jack right?

ok, so audio chip itself is ok.
VCO is locked (thats good)

next thing to do is key up a radio right next to the washington and see if the receive is just very, very weak, or no receive at all.

do you have a walkie talkie or maybe a mobile radio in the car outside your house that you can tape down the mic button, and put it next to a speaker with the car stereo on?

then you can go inside, set the washington to the same channel as the mobile and see if you can hear anything at all, however faintly.

of course we want to eliminate the obvious easy mistakes to make, like, is the RF gain all the way up? (it should be)
are you sure your antenna is connected properly? etc...

i know, i know, how dare i ask, but you'd be surprised how often these things get overlooked.

get back to me and i will type up some more tests/ideas.
LC
 
Ok well i keyed up another radio one of my everyday talkers i use and it does show the washington is recieving the signal on the washington the meter on the washington does move all the way to the right so it is picking up the signal when i play with the rf button the recieve goes up and down as it should just no recieve audio cannot hear myself in the speaker but definetly see the meter bouncing to the right so it is i would guess recieving the signal just no sound for the recieve
 
what we are trying to determine is if any signals are actually making it in to the radio and just not strong enough to be detected, or if there is something blocking them from being received in the first place.

first, use this schematic:
http://www.cbtricks.com/radios/uniden/washington_mb8719/graphics/uniden_washington_mb8719_sch.pdf

if the receive turns out to just be very weak, the radio might have been messed with and someone messed up the receive tuning coils.
dont start turning them just yet. chances are, if this is the case, that they are so out of tune that you could mess them up further before you know it.

if there is no signal being received at all, then the first thing to check is IC5 pin 6. there should be about 8 volts on it in receive.
is there?

if there is, next thing to check is TR9 the first RF amplifier.

you need to learn how to check transistors and diodes using your DMM, and you have to remove the part from the PC board to test it.

here is a link to help you learn how to do this:
Testing semiconductors with analog and digital multimeters

if this stuff seems over your head, then its time to seek out a tech to fix it for you.

other parts to check when getting started are: D13 and D14, D21 and D22, TR13, TR10, TR17, and TR16.

yes, this is a shotgun approach, but without you having test equipment such as a signal generator and a frequency counter (not the kind that connects to the antenna jack), i cant tell you how to check for certain freqs to be present or inject a signal at a certain point to see if operation is restored.

there is also the possibility that an electrolytic capacitor has gone bad/dryed out.

easiest way to check for that is to bridge a good one of the same value across the suspected bad one, but you are going to have to do that on your own.
look around the transistors i mentioned using the schematic, find the associated electrolytic capacitors, and start with those.

sorry to be so general, but as you can see, this is something that could be very easy, or a real head scratcher.

good luck with it,
LC
 
for the benefit of those reading this thread besides Dan, i was typing that last post while he was typing his, so i did not get to hear the results of his tests before posting it.

i will leave it there in hopes that it helps someone else in the future.


Dan,

your problem could be as simple as a loose wire in the microphone.

remove the mic from the radio, and with the radio on, jumper pin 3 to pin 4.

if you were to picture the pin pattern of the mic jack on the front of your radio as a "U", then pin 3 would be at the bottom of the "U".

pin 4 would be the pin just to the right of pin 3.

when you jump them together you should hear sound from the speaker.

if you do, then the problem is in your mic, and most likely a wire has broken loose inside the connector, or inside the cord itself, or even inside the mic body itself.

if you dont hear any sound from the speaker when jumping those pins together, then the problem is inside the radio.

ok, thats all for tonight.
good luck,
LC
 
Ok so i jumped pin 3 to 4 nothing i did however hook up this radio to my antenna and it is definetly picking up a signal meter moving all over and verified this with my other radios definetley ppl talking looks as to if there is a sound problem think the mic jack could be a culprit or someone rewired the mic jack? but i used 4 diffent mics radio seems to transmit ok i did notice however when i plug the mic in and turn the channel selector i here thru the speaker every time i click the channel selector and when i take the mic out of the jac i do not here the little noise
 
ok, i dont think the mic jack has been rewired, but only you can tell that for sure.
look at the back of the mic jack on the radio.
does the wiring look factory? or does it look like someone has been in there soldering wires?

we know that RF is getting into the radio, and we know that you have a path to the speaker that works because of the hum you heard when touching the audio amp.
you tried different mics, and that tells me that was not the issue. (too bad!LOL)

at this point im starting to suspect the AF amplifier transistor or the caps around it.

its TR36, and will be near the audio amp IC. its a 2SC458 transistor, but if you cant find one of those, you can try a 2SC945 just to confirm that was the bad part.
an NTE85 will also work.

you can test TR36 after removing it from the chassis using the method i linked to in a previous post.
caps to remove and check/replace are C107, C108, C109, C110, and C111.

there is also a slight chance that the problem is in the channel muting circuit, so check TR45, which is a 2SA733 or an NTE290A.
also check C198 and C142.

again, sorry to give you such a shotgun approach to this, but we cant go the regular routes without test equipment and experience using it.

aside from that, look for obvious signs of other peoples work around the switches, knobs, jacks, etc.

use this schematic and look around the areas of the parts i listed.
http://www.cbtricks.com/radios/uniden/washington_mb8719/graphics/uniden_washington_mb8719_sch.pdf
if none of my suggestions work, start checking other parts in these areas.
thats about the best we can hope for at that point.
be sure to post back any findings, good or bad.

good luck with it,
LC
 
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