Radio Make and Model: cobra 2000gtl
PCB Number: 497
PLL Number: mb8719
Test gear available: Dvm/anolog m
Symptoms: freq. counter
What is working: entire radio
What has been tried: cobra bulletin 1232
Did it suddenly happen ?: next day
Anything else that may be of help?: hello men,The problem started with dimming of the channel selector and meter lights with the radio turned off, so i changed fets 501-502 in the freq. counter module and everything worked fine,the next day I turned on the radio and the counter read 92.2000 so I changed all the elect. caps replaced Diode 528 with a 1watt zener replaced the following Tr519,Tr 522,Scr501,and it still reads the same.I took another module out of another cobra 2000 I have and tried it and everything was working fine,so theres something in the old module thats bad? The radio works fine,I can change channels and all is good with the original module except the counter continues to read 92.2000 please help..Thank you
Freq. counter
Re: Freq. counter
Hallo I copy this from cbtricks board.Perhaps this helps.
The "92.000" problem really has several possible causes. Only some of those will be found inside the shielded box containing the counter/clock display.
But if the radio has no receive or transmit, I would predict that the counter is NOT the problem. I think the counter is reading just what it should if the radio itself is dead.
Or, more to the point, if the PLL section of the radio is dead. If the radio is not feeding the 35 MHz signal from the PLL into the counter to start with, it won't matter if the counter works or not.
Unless it has something feeding into it from the radio's PLL section.
First place to look will be pin 9 of the MB8734 PLL chip. You should have 8 Volts DC. If not, the problem is in the radio's power supply and/or the transmit-receive switching chip, the MB3756.
I would not recommend messing with the counter until you can FIRST get the radio to transmit and receive.
The "92.000" problem really has several possible causes. Only some of those will be found inside the shielded box containing the counter/clock display.
But if the radio has no receive or transmit, I would predict that the counter is NOT the problem. I think the counter is reading just what it should if the radio itself is dead.
Or, more to the point, if the PLL section of the radio is dead. If the radio is not feeding the 35 MHz signal from the PLL into the counter to start with, it won't matter if the counter works or not.
Unless it has something feeding into it from the radio's PLL section.
First place to look will be pin 9 of the MB8734 PLL chip. You should have 8 Volts DC. If not, the problem is in the radio's power supply and/or the transmit-receive switching chip, the MB3756.
I would not recommend messing with the counter until you can FIRST get the radio to transmit and receive.
Re: Freq. counter
Hi dxswe Thanks for the response,the radio works great,the channels 1-40 and ssb all work fine, the only problem is the counter reading 92.0000,if you read what I have done to the freq. module you will see what I have done,I just don't know what other part or parts to check in the module. Thanks, maybe someone will have a clue as what else to check.
Re: Freq. counter
ok i always have a night light on in my radio room,i did not have it on lastnite and noticed the channel selector light and meter lights glowing dim,does anyone know what capacitors are connected to the vcc of the display matrix,so i can check them. Thanks again