The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Hello folks,

I have aquired a Whistler 700 mobile from my father and have tested it on my 25 Amp power supply. It doesn't power on when I turn on the switch.
I have a couple of questions regarding this radio, hoping you guys can help me out.... I have already checked the in-line fuse and its fine.

1) Who makes the Whistler 700 mobile?.
2) What should I check to determine why the radio is not getting power?
3) Can anyone provide a diagram of the circuit board and what should be checked for the no power issue?.

Thanks in advance..


HQS

just inside the radio is a diode right by where the power wires come into the radio this is the reverse polarity doide if the radio was hooked up backwards this diode will pop and split in half replace it noteing the position of the banded end with another diode and you should have power restored to it .

Hello.

Thanks for the reply. I took off the case and had a look at the diode. It seems to look in good shape. I checked the wires over that are attached to the power plug and found that the ground wire had melted on one of the RF chokes. I removed the wire and replaced it, turned the radio on and it fired up no problem!. Everything lights up and and when I key up the mic, the bars show transmisson, but there is no modulation.It's like throwing a dead key.

There is no recieve or sound coming from this radio. The squelch is turned down and still no sound. Do you happen to have any ideas on what to check next?.

Thanks in advance,

HQS

Check the audio chip it sounds like it has gone south.

Rick.

Thanks Rick...


Any idea on which chip may be the audio chip in this Whistler 700 radio?.
I would love to get s schematic if this oard if I could.

Thanks,

HQS

To find the audio chip, follow the wiring from the speaker indirectly it will end up at a transformer the other side of the transformer is the audio chip, it is usually bolded to the side of the radio, it may have a number like (TA7205). As for a schematic diagram if you can let us have the number of the PCB and the PLL number it may help in trying to track one down. Hope this helps, let us know how you get on.

Rick.

Hello again..

Thanks for the replies!.

I followed the power wires and cannot locate a chip that has the TA designation on it.

The board is 4A1002B with the LB1407 PLL chip. All I see on the board is transformer, resistors, capacitors but no TA7205 or TA callout.

Would any of you happen to know a schematic for this type of board and chip?.


Thanks again!

HQS

With not knowing the radio it is not easy to help, but if you can let me have a list of the IC I will see if I can identify the audio IC. It?s the speaker wires you need to follow not the Power wires. If your intension is to get this radio up and running again it maybe necessity to draw your own schematic diagram this sounds worst than it is you just need to take your time. Do you know how old this radio is? As the PCB number did not help.

Rick.

plug an external speaker into the pa plug on the rear or the radio put the radio on pa and try talking into the mic if you have audio its not the audio chip. Is whistler the brand name? Is there a manufacturer on it any where? If you can find any info let me know and I can probably find a schematic or some Info on it ....Thanks Chia

Whistler 700 cb radio was made in the late 80s and is almost the same as the Magnavox WT109 and Omnivox 9125 the pcb number i have is 401085A or B. 1st gen used a two trans in a hybrid push-pull array and jmax transformer 2nd gen used upc???? chip af amp but i do not remember the number. Good luck in finding a diagram as in 40 years of working on rigs i have never seen one. as there is not much to this rig it should be easy to get going again.

Pic of the Whistler 900 www.rigpix.com/cbfreeband/whistler_900.htm

James.

Hello,

The picture in the link below is exactly the same looking radio that I have except it is the 900.
Thanks for all the great advice on troubleshooting this radio as when is comes to them, I am relatively new.
The # on this board is 401085 C. The PLL chip is LB1407 7F6.

I haven't tried hooking up a speaker to the PA yet, that will be the next step to determine if the audio chip is blown or not.

Oh ya... this radio was manufactured in July'87

Thanks again eh!


HQS

Ive got some places to check and Ill let you know If I find....Chia

Hello folks...

I tried hooking up a speaker to the PA and keyed up the mic. No Sound came through the speaker. Several TX lights came on and my AMP meter shows 2Watts TX but no sound. Does this mean that the audio chip has gone south?.
I cannot seem to locate this chip, What does it look like?

Thanks in advance

HQS

It may be a discrete audio amp in there.

Lets us have a list of all the IC or chips and then someone should be able to let you know which it is.

Rick.

i just got a whistler700 for 20 bucks seems to be a good radio, but cant find anything on it any help? thanks

If its tuning info you want:::::R225 Is the amc limiter
L304,L305,L306 is the Am Tuning Slugs....
But i would not recommend cut the resistor R225 out of
circuit...I would do it this way...Locate Q205 Transistor
Unsolder the collector (Center Pin) of Q205 Amc Shunt
and install a 10K resistor in series with the collector of Q205.
Doing this instead of just clipping R225,,will allow for good
modulation and swing without being overmodulated as bad.
And B.T.W.. The Audio Chip should be located on the Right
Side Rail of the Radio, with the radio facing you,(Knobs forward).
You will not be able to see the numbers because the numbers are
facing the inside..In order to see the numbers you must remove
the screw holding the chips base tab to the chassis rail,and pull
the chip back from the rail..It probably will be a TA-7205,,It is a
10 pin I.C..