Galaxy 2517 mosfet version, transmit problem

[longhaireddwb]

I'll do my best to describe what is happening. Its just too late for me to back in and work on it any more tonight, but here is the problem.

A guy from work brings me this radio and said that he thinks the finals are burnt because it is showing less than a watt on his meter. I open it up and check the voltages on the resisters in front of the finals that receive the power from the VR's. I was told by Galaxy a couple years ago that this is the easiest way to check the voltages on the mosfets. If there is around 3.5 volts and when you turn the pots that control the voltage to the finals if they adjust up and down then there most likely alright.
What I found was they are adjusting but only reading 0.83 volts or so. This goes the same for both finals and the driver. Of course all three of these are the 520's.

Next I got to looking at the pre-drivers. I found the resistor (r246) that goes to ground from the pre-driver(Q51)(NPN) was burnt and the pre-driver was not working properly. I replaced the pre-driver, resistor and the cap that is also goes to ground along with that resistor.

Fired it back up and smoked the resistor again and the transistor.

I'm thinking my next step is to work my way back before Q51 and see if there something else not right. I see no tell-tale signs of anything else and this radio has not been volted or anything like that. A receive mod has been added but nothing stupid.


So does anyone got any ideas or has ran across this before? Or can offer some verbal assistance?
Thanks as always from A guy that probably shouldn't be messing with radios and know enough to get himself in trouble...
Jerry...

 

[ExitThirteen]

I'm still thinking that maybe you have a bad MOSFET. What you can do is replace the pre-driver and resistor again, but instead of firing it up, desolder the "Gate" legs of the driver and final MOSFETS, then fire up the radio. If the radio powers up and doesn't burn out that resistor, then your MOSFETS are bad. I always do this when troubleshooting a MOSFET radio with a TX issue, that way I can eliminate the finals out of the picture, since MOSFETS tend to go short rather than open when they fail. If you desolder the gate legs on the MOSFETS, and the resistor still burns up, then you know it's an issue other than the finals, that will at least get you pointed in the right direction. Let us know how you get on.


~Cheers~

 

[longhaireddwb]

Well I hate to say it but
IM A DUMB ASS!!

I got a chance to go back into this radio and with a clear head and not sleepy. What I found was THIS IS NOT A MOSFET RADIO LIKE THE GUY TOLD ME IT WAS!

I did replace the resistor and the predriver that was next to the resistor. I found that after looking at the specs on both factory and aftermarket parts on the TR that the leg config was different. So I put a new TR in and got the legs in the right positions and now the resister don't burn up! :headbang

OK, got that problem fix. Now I still don't have any power out. I disconnected the driver and finals and tested then and they read good. I'm still not seeing more than 0.7volts at the driver and finals.

Shouldn't I have more DCV at that point?

sorry for being a dumb ass!
Thanks to "Exitthirteen" for answering my post. I was afraid I did something wrong and pissed off a bunch of people and thats why nobody was answering me.

Anyway. Hope to get a reply to this question.
I sent an email to Galaxy to get some help from a tech on this. If he gets back with me next week I'll post up what he said and what I'm going to do next.

Jerry...

 

[ExitThirteen]

That's no problem, I tried to be of some help! LOL Anyhow, I can help with maybe tracing down some voltages here in a day or two, as I work 12 hour days on a weekend shift at work. My weekend time is real limited, but come monday or so I can poke my head into some notes and tell you where to start probing for voltages and such then. If you hear from a Galaxy tech, I'd also be interested in what he tells you. Let us know how you get on.



~Cheers~

 

[longhaireddwb]

I sure will.
Thanks again for helping this Dumb Ass. And I will welcome any more help you pass this way. I work long hours during the week but have Fridays off because of my new Winter schedule. And they are talking about snow again on Wednesday so if I'm off then I'll call the Galaxy rep as he did send me an email with his phone number and hours of work :w00t: so I will be calling him.

 

[ExitThirteen]

Have you gotten any further with the Galaxy? Just curious.


~Cheers~

 

[longhaireddwb]

The galaxy tech wasn't a lot of help. He said to check the voltages at the am tr on the side of the case (TR54). I checked it and had 13+ on the two outside legs and 2 on the inside leg. This is the same reading I'm getting at TP7, 8 and 9 and at the finals. Still I think the voltage should be higher than 2 at the driver and finals Right?

I'm about done with this thing. I'm going to give it back to my buddy and say send it somewhere as I just don't have the time or will to keep searching on it.

And BTW, Its not a mosfet radio. It has the 2312's I think they are. Sorry for the confusion.

I got laid off my job after 4 years so I'm a bit out of it and just don't have the paciance .

If someone can help point me to and idea to get this thing fixed great! If not then back it goes.

Thanks to all that offered help and to anyone that will still help.

Jerry.

 

[drpill]

I got the same radio doing the same thing. My finals checked out ok but i was thinking it was maybe another part of the transmitter circuit like maybe the dual operational amplifier (NJM4558) or the balance modulator (AN612) or AF power IC8 (TA7222AP) Dont have much experience with this unit though looking for some help If anyone Know A good way to check these part please post