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2970N2 help
- Thread starter n4dxx
- Start date
Robb, you are right. The 520's can't withstand anything over 5V, that's why I've seen so many problems with the N2's... Most are set way too high from factory, or some hack was twiddling around in there trying to get more power.
The guy at the local CB shop (who I do tech work for on occasion) has 4 or 5 of those PA boards from the 98VHP's and the N2's in his drawer that were smoked so bad that they caught fire. Literally caught fire.
I pulled a board out of that drawer that was from a Galaxy 94HP that was damaged, but was salvageable... so I saved it. Works like a champ now.
~Cheers~
The guy at the local CB shop (who I do tech work for on occasion) has 4 or 5 of those PA boards from the 98VHP's and the N2's in his drawer that were smoked so bad that they caught fire. Literally caught fire.
I pulled a board out of that drawer that was from a Galaxy 94HP that was damaged, but was salvageable... so I saved it. Works like a champ now.
~Cheers~
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Wow i can only get 2.9 volts on the gates on the main pcb all the way up!!!
Wow, that's weird... you should be able to easily adjust them to 3.75/3.5V with no problem. Something just doesn't seem right there.
Ok, let me ask this.... are the driver and finals all IRF520's? Or are they bipolar transistors (C2166/2xC1969's)?
~Cheers~
Ok, let me ask this.... are the driver and finals all IRF520's? Or are they bipolar transistors (C2166/2xC1969's)?
~Cheers~
Oh yes! It can. SSB APC should be set @ 12.5V. That is adjusted at VR18 and TP8.
Good call on that, that slipped past me... Normally those aren't messed with on the N2's that often.
~Cheers~
Good call on that, that slipped past me... Normally those aren't messed with on the N2's that often.
~Cheers~
Uhh... yuck, that's definitely not right. I wonder if the pass regulator transistor is bad. It'll be the large transistor bolted along the right side of the chassis towards the back. It'll either be a B754 or a B827. If that has gone fault, it may cause a low power condition with the SSB APC.
~Cheers~
~Cheers~
Ok here is what i have found..I replaced the b827 No joy ...However if i run vr15 up to 6 volts i then can get vr 18 up to 12.5 But the radio key's 150 watts on am and i can't get it any lower...Wow at least i am learning and this radio has been this way from new..Hummm...according to the service manual you set vr 15 first then vr 18 so this may be correct but the 150 watt dead key is not..Maybe a bad low power VR?I will sleep on it and get with you tomm..Thanks for all the help
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Hmm... interesting. 150W deadkey on AM = ouch. Yes, we can work it out tomorrow. Have a good night. 
~Cheers~
~Cheers~
AM APC = 6v
SSB APC = 12.5v
Those are the correct settings. Sounds like the 2SB827 transistor - or its companion part - has a fault. Loss of AM Regulation.
SSB APC = 12.5v
Those are the correct settings. Sounds like the 2SB827 transistor - or its companion part - has a fault. Loss of AM Regulation.
Yep, Robb is right on the money. And the SSB output is also regulated thru the AM pass regulator transistor (very poor design). Which is why you couldn't get 12.5V on the SSB APC without adjusting the AM APC to the correct voltage.
What needs to go in there is a TIP36C instead of the 2SB827. And replace the 2SA1869 with a TIP42C.
~Cheers~
What needs to go in there is a TIP36C instead of the 2SB827. And replace the 2SA1869 with a TIP42C.
~Cheers~