Help needed with Old President Grant PC409AB Issues

[bigtoyboy01]

Hello all, I'm new here and this is my first post. I've recently got into CB radios and acquired a few older CB Radios. I love fixing things and I'm enjoying the challenge of potentially fixing this radio. I took it to a reputable repair shop and he said it wasn't worth fixing, but I suspect he didn't even open it up.

The one I'm trying to troubleshoot is a President Grant. The board says PC409AB on it. The problem is it does not transmit, or receive, the PA function doesn't work, and when you first turn it on, within 5 seconds, the channel display fades to nothing and usually won't come back until the next day, at which point it will fade to nothing again. I did get the channel display to stay on for a while once, but it was weak on the dim setting so had to keep it on bright, but that didn't last long and reverted back to fading to nothing.

So far I have cleaned all of the knobs/pots with deoxit, removed and tested the C95 cap, noticed that the TR24 transistor has been removed, and removed and tested the C84 cap, because it looked like it had leaked a brown substance, which I now believe to be glue. I also purchased a new mic from Amazon, this radio has a 5 pin Mic. The radio has 3 switches that were added to the bottom, but I have cut the wires to all of them so I could get the bottom cover off...the wires had no slack.

What should I check next? Thank you in advance.

 

[AudioShockwav]

At this point I would replace all the electrolytic cap just for good measure, they are just that old.
Nice old radio.....

73
Jeff

 

[bigtoyboy01]

Thanks for the reply Jeff. I found a cap kit for my radio at Klondike mikes, but it would cost me $51 after shipping and taxes, that seems high.. what's the most economical way to buy quality caps? Any certain brands to look for?

 

[nomadradio]

The switches most likely served to expand the frequency coverage above and below the legal 40 channels. To get the normal 40 you probably need connections that were being made through those switches. I'll see if I can find pics of what that section of a PC409 radio should look like before that modification was made. Odds are you'll need to restore some connections to the MB8719 chip that were broken when those wires came loose.

73

 

[Dr. Frankenstein]

@nomadradio

If the mod was done right and the cuts where jumped with resistors it should still work.

What we don't know is if either of them are center-off, or if one of them is set up as a "10Kc" switch.

With that much work done to that radio, I bet the clarifier was clipped too.

Someone paid big bucks to have that radio modified back then.

But yes, you are right those wires may need to be reconnected if he wants to have any of the upper or lower channels.

 

[bigtoyboy01]

I can jump the switch wires back together back together, I just cut them to be able to take the cover off...there was no slack at all. Even with the switch wires intact, the channel display still faded to nothing and had no transmit or receive. I'll get some pictures soon.

 

[AudioShockwav]

Mike uses quality caps in his kits, I don't know if shipping has skyrocketed in Canada and that drove the price up.
He is a member here, might contact him and see if he could find a cheaper solution for shipping.
Try a direct message to him
@Klondike Mike

73
Jeff

 

[Eldorado828]

I agree with @AudioShockwav
You can't go wrong his kits. It saves you the homework of sourcing the caps, they're quality and they'll be correct. I've personally bought kits from him a few times now.

 

[Klondike Mike]

... I don't know if shipping has skyrocketed in Canada and that drove the price up.

Nope. 35% tax on ANYTHING entering USA.

The supreme leader decider has decided to take money from its citizens for every product you buy from outside the country.

https://klondikemikescapkits.com/blogs/news/no-more-de-minimis-imports-for-usa-customers

 

[bigtoyboy01]

 

[bigtoyboy01]

 

[bigtoyboy01]

 

[bigtoyboy01]

The wires to the add on switches that I cut are near the channel selector on bottom of board.

 

[CSA1863]

Here is what the board should look like without the channel mod.

 

[bigtoyboy01]

Thank you CSA1863. So it looks like there is a resistor and a jumper in my radio around the near the PLL that are not stock...other than the cut wires. Shouldn't one of the PLL pins have around 8 volts on it? The 2 3-pronged devices that are heat-sinked to the back of the case, are those voltage regulators? Anyone know what the voltage should read there? Anyone have a service manual with troubleshooting steps?