FT-2800M No Power On

[digitalchaos1980]

Hi guys, hope everyone is having an excellent Valentine's Day! I have recently aquired a Yaesu FT2800M 2m radio. The radio was allegedly connected during an electrical storm and lightning hit outside the station it was in and everything got hit from what I hear. The fella who gave me the radio said he did not have the time or patience to try to diagnose it. So he gave it to me. I have a strong electronic background, but I think I need to ask for help with this lol. What I know so far is when connected to electrical power, nothing happens at all. No significant power draw, no fuses blowing. The polarity diode is fine still. I have 12v going to the PA transistor and driver, 12v at the microprocessor and 12v going to the radio head. What I DON'T have is any voltage at all going into or coming out of the 7808 regulator IC. I have looked over the service schematic a few times and tried to get voltage readings of the power circuit, but after a while it starts to get confusing, I get frustrated and set it down til I get brazen enough to get back into it. I want to get this sucker going! Does anyone with experience have any ideas or suggestions? I don't have the money to buy a radio or send it to get repaired. I have the know-how and plenty of time, just need a nudge lol. Thanks everyone for their time reading this and thank you in advance for any help offered!

Chuck

 

[rescue161]

If you don't have voltage going into the 7808, then go back to the component before the 7808. Half split troubleshoot. There is an "open" somewhere. At least you know that voltage is not making it to the VR.

 

[digitalchaos1980]

Thanks for the quick reply! If I recall correctly, the component before the VR IC is another transistor, but unfortunately I think it is a surface-mount component, so it'll be loads of fun to check haha. I will check into that tonight or tomorrow and post back with findings.

Chuck

 

[SCPD]

Unfortunately a very common problem with the 2800s....

 

[digitalchaos1980]

Haven't had the chance yet to further troubleshoot, but according to the service schematic there are 2 other transistors (surface-mount) that feed to the VR IC. I'm gonna have to find a way to pull those and test em I reckon. As for this "being a common problem on the 2800s..." would you elaborate on what you know about it? I really don't want to throw this sucker back in my goody box lol.

Chuck

 

[rescue161]

You shouldn't have to pull them to test them. Just check for voltage on each leg and read the schematic. You'll be able to tell whether it has an open junction.

 

[mikepdx]

Check out this thread at QRZ:

Yaesu FT-2800M Protection Diode

are you positive it's ok?

The entire Service Manual is available here:
http://www.repeater-builder.com/yvs/pdfs/yaesu-ft-2800m-technical-supplement.pdf

 

[digitalchaos1980]

You shouldn't have to pull them to test them. Just check for voltage on each leg and read the schematic. You'll be able to tell whether it has an open junction.

Thanks, I'll check it out. If I determine one is bad then I'll simply get me one to put in its place. But I do hate working with those tiny parts, uggh lol.

Chuck

 

[rescue161]

You may find out that those parts are actually good and the open is somewhere else. As Mike pointed out, the protection diode may be open.

 

[digitalchaos1980]

Check out this thread at QRZ:

Yaesu FT-2800M Protection Diode

are you positive it's ok?

The entire Service Manual is available here:
http://www.repeater-builder.com/yvs/pdfs/yaesu-ft-2800m-technical-supplement.pdf

Yes, I am sure it is ok. It had been switched out by the fella who gave it to me. When it didn't fix it, he didn't want to go further. When connected to power, I have no significant power draw and no fuses blowing. I have 12v getting into the radio to the PA trans and driver, microprocessor, and to the radio head. Just nothing going into or coming out of the voltage regulator IC. I also have that service manual I believe, if that's the one with the schematic in it lol.

Chuck

 

[digitalchaos1980]

Could it still be the prot diode even if there is voltage getting into the radio? I always thought if it shorted, it would cause a direct short from + to - and blow a fuse or pop a breaker. Or if it opened, then it wouldn't change anything, there would just be no protection. Am I wrong?

Chuck