President Madison-$25 does not transmit, fixable?

[Red Ranger]

I found a very nice shape President Madison, it is at a "bargain barn" it has on the tag that it does not transmit.

They are asking 25 bucks. Can this radio be fixed economically? I THINK it is the four pin version, will have to go back and double check.

 

[Big Dummy 123]

Yes it well woth 25 buck if all there and can be fixed

 

[Big Dummy 123]

Buy ill give ya 50 buck and shippp for it

 

[Red Ranger]

It's in really good cosmetic shape, could be something as a broken mic cable or the PA switch is turned on. :sneaky2:


or blown finals.... but it also has the external speaker on the left, the whole radio is in great cosmetic shape, and I was talking to some locals. They said that shops were selling that speaker for like $50!

They said that there are plenty of Cobra 2000's out there with no speaker, or one that is hashed and thrashed, and folks would like to have a matching set.

If it does have blown finals, or perhaps the keying relay is bad, how available are spare parts?

 

[loosecannon]

buy that radio.
now that you've talked to locals about it; you'd better buy it soon!

it can be fixed.
spare parts are readily available.

it is a great deal.
when you get the radio home, check it all out, and if you cant get it to TX; make a post here, and we'll run through some tests to find out why it doesnt work.

even if you cant fix it yourself, 25 dollars for this radio is too good to pass up.

if you sent it to a shop and the repair cost you 100 dollars (very good chance it will be less than that), you will still be ahead of the game.
just look at what they go for on ebay.

good luck,
LC

 

[Red Ranger]

OPPS, it's actually a President "Dwight D."

and yes it does not transmit, it does turn on, the CLOCK works. I key the mic and get NO dead key(the TX light comes ON), receive is very very LOW to none(with squelch all the way down) tried a different speaker, still very low static level.


SOME of the buttons are touchy, when I turn the radio on it "pops" thru the speaker, and after I unkey the mic it pops also.

I'm going to open it up and do some contact cleaning....

I don't see ANY SSB on this radio!

according to this thread: http://www.worldwidedx.com/cb-band-cb-radios/24194-president-dwight-d.html

I need to be looking for blown caps? If my power supply was bad, then how would it light up? I'm going to put it on a external DC supply and see what that does.

 

[slprydk]

OPPS, it's actually a President "Dwight D."

and yes it does not transmit, it does turn on, the CLOCK works. I key the mic and get NO dead key(the TX light comes ON), receive is very very LOW to none(with squelch all the way down) tried a different speaker, still very low static level.


SOME of the buttons are touchy, when I turn the radio on it "pops" thru the speaker, and after I unkey the mic it pops also.

I'm going to open it up and do some contact cleaning....

I don't see ANY SSB on this radio!

according to this thread: http://www.worldwidedx.com/cb-band-cb-radios/24194-president-dwight-d.html

I need to be looking for blown caps? If my power supply was bad, then how would it light up? I'm going to put it on a external DC supply and see what that does.

Not SSB but still a good radio, I think they had 2 versions, one had an 858 PLL, this board would be similar to the Cobra 29XLR I think, the newer version would have the 2816 PLL and should be about the same as a Cobra 1000GTL. If I am wrong somebody please chime in. In either case it could be a nice radio for $25.

Do the lights look dim? do you hear a hum in the speaker? Do you have a volt meter to check the output of the power supply when you open the radio?

 

[Red Ranger]

looking through the insides, there seems to be surface oxidation on everything..

and a diode was clipped...

and a switch on the bottom labeled "High Med Low" seems to be some sort of expansion, there are two crystals on this extree board

When I toggle the switch it is obviously "changing bands" LOL.

Looks like the "Finals" have been messed with before, this radio looks hacked!

Do the lights look dim?

Maybe a little

do you hear a hum in the speaker?

No hum, just a low level of static(at high volume) I can hear the squelch threshold, and the static is unaffected by the RF gain knob.

Do you have a volt meter to check the output of the power supply when you open the radio?

Yes I do, I assume it is supposed to read 13 volts?

I put the volt meter to the finals, and was getting NOTHING on any of the legs, just read 001 volts, could be a ghost reading.

I ran the Radio off a DC power supply, still the same issues, all the caps look good. No signal is making it to the finals.

I probed the pin side of the mic connector, the stock President mic had a short in it(intermittent), installed a Cobra mic and fixed that issue, but still no TX.

 

[loosecannon]

first we need to know which version you have.

find the PLL chip and see what numbers are on it.
it will be either UPD858 or UPD2816.

try touching the wiper lead of the volume control with your finger.

do you hear a hum in the speaker?

im thinking the best place to start looking is the voltage regulator.
check the voltages, and if they are not correct; replace it.

if they are, start tracing the voltage till you lose it.
LC

 

[Red Ranger]

Any Ideals where I can get a schematic of this radio? The voltages to the radio are good, 13.9 Volts.

I can't seem to find a good schematic of the board anywhere, the chip on the board says:

NEC KB3219
D2B16C (maybe that is D2816c?)

first we need to know which version you have. find the PLL chip and see what numbers are on it. it will be either UPD858 or UPD2816

I think I got the UPD 2816.

 

[loosecannon]

this is the newer version, and is actually quite similar (almost identical) the the 29LTD chassis.

the parts numbers will be a bit different though, so dont go by a 29LTD schematic alone.

i think the closest approximation of your radio that has a schematic online is the cobra 1000GTL.

here is a link to that schematic:
http://www.cbtricks.com/radios/cobra/1000gtl/graphics/cobra_1000gtl_main_sch_a_size.pdf

take a look at it and see if the part numbers line up to what you see in your radio.

im pretty sure they are the same, but only you will be able to tell for sure.

good luck,
LC