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Hi there,

Grettings from Portugal

Radio Make and Model: President Jackson II (new model)
PCB Number: PB-351AB 1/4
PLL Number: Z0740B6
Test gear available: Autoranging multimeter and frequency cunter (no oscilloscope)
Symptoms: No output needlle doesn´t moves
What is working: Everithing else work´s
What has been tried: check for shorts on the non SMD transistors
Did it suddenly happen ?: Not sure
Anything else that may be of help?: This radio arrived with the coil attached to the negative pin on the plug (on the rear) broken/opened and the PCB around it all black

I repair TV´s and a friend asked for help on this radio.

We have tested it in my shop, and it only receives, when we press the PLL nothing happens, the needle doesnt moves (no output)

I have searched on-line for the esquematic but didnt found it.

Any help would be appreciated

(SORRY MY BAD ENGLISH)

Best regards
Nezocas

negative pin on the plug (on the rear) broken/opened and the PCB around it all black

It's been reversed with too large a fuse, this will take out the protection diode, causing the burns.

Remove the diode to get it working = All OK as long as you don't reverse it again.

Reverse it again without the diode being replaced = blown modulator, driver, and final transistors.
This will give you the no transmit symptom.

Cure: replace the modulator, driver, and final transistors.

Hope this helps

Hi there,

Thank´s for the tips.
Just arrived at my shop, and tested the protection diode, and its fine.
Probably the final transistors/modulator or driver defective as you say. Can you give me these components location on the board.
I have a TDA2003 (sound amplifier) near the affected zone (near L502 coil).

Best regards
Nezocas

and tested the protection diode, and its fine

In that case the thing could have had 24V fed to it, or a positive voltage on the -ve lead.
Or the diode might have gone open, or the track to it might have gone open.
Not much else in that area that could draw enough current to burn up like that.

Have you tested it "under load", like turning the radio off and connecting a power supply reverse polarity deliberately, current limited to 500mA or so?

Can you give me these components location on the board

They will be in TO-220 cases, most likely bolted to the back panel of the radio for heatsinking purposes.
Don't know that exact model, but 99% of all radios are identical in this regard.

I have a TDA2003

If it receives, then that IC is OK.

Hi there,

Transistor´s arrived today....just placed them, and problem solved.

Best regards
Nezocas