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2995dx modulation on a scope

359 said:
I only have a few minutes a day between sleep and work, but why would I have 13.5v on TP8&9?
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Dumb question, and please don't take it the wrong way.
Where are you grounding your VOM for testing? If on the chassis of the
radio you will get strange readings. Find the radio's actual ground plane
connection and use it. (one radio I have has a wire soldered between to
coil cans and I just clip to that)
Anyway, just an idea. (reason being that happened to me.......I know,I'm
different and everyone else does it right!!!! :LOL:
trucker
 
I wanted to mess with it Saturday, but I saddled up and rode all day instead since it was nice. I'm cleaning up my bench a little as we speak and hope to get some time this week after work.
 
Well it's 3am and I didn't find much.

Q43 should be off while radio is keyed, and it is.

Q41 collector should show ~1.5vdc while radio is keyed, but it shows 0vdc

Driver bias should show 10ma, and it shows 117ma at 3.44vdc

Final bias should show 100ma, and it shows 42ma at 3.14 and 3.03vdc

Looks like the driver may be fried, but what else is damaged is the real question.
 
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Well I sat down tonight and started adjusting up the bias voltages to see where the currents went out of curiosity, and my power supply went deader'n hell ....... 0 volts. Brand new VS-70m, just over a month old :glare:
 
359 said:
Well I sat down tonight and started adjusting up the bias voltages to see where the currents went out of curiosity, and my power supply went deader'n hell ....... 0 volts. Brand new VS-70m, just over a month old :glare:
Click to expand...

Replace the LM-723 IC regulator chip on the power supply board. It's such a common Astron failure they mount the chip in a socket for easy replacement.
 
JoeDirt said:
Im assuming you have mosfets!
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yup

Shockwave said:
Replace the LM-723 IC regulator chip on the power supply board. It's such a common Astron failure they mount the chip in a socket for easy replacement.
Click to expand...
My wife works at OSU, having her stop at Universal Radio with it will be just as fast as ordering a new chip, but if it was any older than a month old, I'd probably just order the chip.
 
JoeDirt said:
Im assuming you have mosfets!
Click to expand...

That was a pretty quick answer I gave heading out the door. But yeah, and that's part of the problem. Most of the info available is regarding the 2sc2166. I did however look at some Galaxy radios, and I think it's the 98vhp that is a similar build to the 2970 and it gives the V and I. The V is a little higher on the Galaxy, but still within the 4vdc limit printed in the data sheet, and the I is the same.

What it comes down to is, I've never played around inside a radio. I always had the local that I bought them from set them up, and never had any problems with any of them to give reason to poke around inside. So here I am with a relatively new 2970n2 probably heading to the parts bin :D
 
I'm so pissed right now I don't know what to do. I took the cover off of the 2995 expecting to see the same diode, and I did. So I removed it, thinking I was just going to stick it back to stock form and use it for reference (I think the only major difference is dual final vs. single final). Well then I realized that the mod limiter had been defeated, unlike the 2970. But also unlike the 2970, Q43 had not been tampered with. The collector of Q43 had been unsoldered and re-soldered on the 2970 it looked like, but on the 2995 it looked original. So the search was on!! I finally noticed that the collector of Q68 had barely been lifted from the board. So I applied a little pressure to the top of it with a dental pick and hit it with the soldering pencil and bingo, I got my modulation control back. HOWEVER, now I have no power, just like the 2970.

I bought both of these new back around the first of the year from someone who I have spent thousands with, and thought he was doing these radios right. The few local reports I got said I was clear, but not loud. I assumed it was the nature of the RCI and the locals being used to that over-modulated Connex/Galaxy sound, which I didn't want anyway. The problem was, I was running a 30-50w carrier on these radios not 3-5w like he set them up to be run. I guess ignorance is bliss, if I hadn't bought that damn scope I would have never known and I wouldn't have $1000 worth of junk radios on my desk.

All this time, I just ran his radios freeing up my time to read about beam antennas, propagation, power tubes, etc ........... I guess I should have been reading about radios instead and paying more attention to what he was doing, because I have no clue where to start looking at what else he may have removed/modded, and as far as I know there are no new manuals for the latest revision of these radios either. :mad:

I did notice that D106 is missing on the 2995 and had some epoxy looking stuff on the board in that area. C269 was also bent over that area concealing it, and not bent over in the same direction as the 2970. It looked like a rain drop that dried there. So I picked at it and it seemed rubbery, more like hot glue than epoxy because it came off after a little work. Anyway, I'm not convinced that the 2995 should have D106 because the two boards are powered from different points.

Oh yeah, and the bias on the driver was cranked WFO too, nice huh? (y)
 
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Well im happy you got it working, It takes years of radio work to find and accomplish what you have figured out in a few weeks!

Now when are you going to finish that NPC mod?
 
OMG so many of these transistors and diodes listed in the service manual are obsolete :angry:
 

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