Topics

Problem with 50W amp..


Gwen Patton
 

Hey, All.

I finished building the QCX amp best I could, but I'm running into a serious issue, and think I MAY have fried one or both of the finals...or messed something else up, I'm not sure.

It powers up ok. No smoke. Nothing seems to be getting overly warm. With the QCX in practice mode and the keying line connected, when I key the QCX the red light comes on in time with the key. I did what the instructions say about adjusting the trimmer, and it seems to be okay. But when I take the QCX OUT of practice mode and try to key the amp, things get weird.

On the QCX, it seems fine for the space of two dahs. Then the letter "P" comes up to the left of the S-meter graphic (I know this is also on when in practice mode, but that mode is definitely OFF at this point) and the unit ceases transmitting. It takes a few seconds for the QCX screen to clear, then it will key up again, but once more, it's only very briefly, then it fails again, same thing.

I've tried THREE different power sources for the amp. I've tried it at 12v, I've tried it at 20v, no difference whatsoever. It just falls over a second or so after being keyed, and it doesn't seem to have anything to do with the QCX end or the power supply. So I'm pretty sure I munged something up in construction. Now, the reason I think I may have fried at least one of the final transistors is that I got a $^@#$ consarned solder bridge on one transistor's connections, and it was a total pain in the ARSE to get rid of. I probably wound up heating the transistor too much in the process, but even with my heavier iron, it was really hard to get the solder enough to flow and get out of the bridge, even with lots of flux and fresh braid. I finally got it, but I think the damage was done at that point.

I don't SEEM to have shorts to ground or anything. One leg of course is connected to ground, so that's understood. Checking for shorts with the other legs, one has no reaction, the other shows continuity for about half a second, then it stops. That's on BOTH transistors, so if that's a sign of being blown, I blew 'em both. :/

IF, however, this sounds familiar, and I have some other issue going on, or anyone can think of some checks I can do with meter or wiggle scope, let me know what to check and to look for, and I'll try it and post back. I think I have some of those finals in my stock in case I need to replace them, but I want to narrow it down a bit before I go that route.

73,
Gwen, NG3P


George Korper
 

Ok this i have done. First after removing IR 510's you must clean the bridges in between the pads. 
I use M.G. Chemical solder braid # 452, but once you get a bridge between pads, it takes a magnifier and 
maybe an Exacto knife.You had to fry the finals and just go in there and bring everything back to where it was. 
You can check the transistors but the sad fact is it is easier to remove and go back to an initial condition than screw around. 
I have built quite a few and the last thing you want to do is rush and burn out all the traces. One slip and a cascade of trouble can happen so never probe around with the final in operation. Also bad finals can cause the problems you are seeing. The keying circuit can be
affected...not sure how but I've seen it. But check the keying circuit with a DVM any way.
And cool down, you'll find it. Take it easy but take it. Sometimes I just break em in half an order another one. 
Lately though they seem easy after the first half dozen. YOU ARE NOT ALONE!

On Thu, Apr 2, 2020 at 5:29 PM Gwen Patton <ardrhi@...> wrote:
Hey, All.

I finished building the QCX amp best I could, but I'm running into a serious issue, and think I MAY have fried one or both of the finals...or messed something else up, I'm not sure.

It powers up ok. No smoke. Nothing seems to be getting overly warm. With the QCX in practice mode and the keying line connected, when I key the QCX the red light comes on in time with the key. I did what the instructions say about adjusting the trimmer, and it seems to be okay. But when I take the QCX OUT of practice mode and try to key the amp, things get weird.

On the QCX, it seems fine for the space of two dahs. Then the letter "P" comes up to the left of the S-meter graphic (I know this is also on when in practice mode, but that mode is definitely OFF at this point) and the unit ceases transmitting. It takes a few seconds for the QCX screen to clear, then it will key up again, but once more, it's only very briefly, then it fails again, same thing.

I've tried THREE different power sources for the amp. I've tried it at 12v, I've tried it at 20v, no difference whatsoever. It just falls over a second or so after being keyed, and it doesn't seem to have anything to do with the QCX end or the power supply. So I'm pretty sure I munged something up in construction. Now, the reason I think I may have fried at least one of the final transistors is that I got a $^@#$ consarned solder bridge on one transistor's connections, and it was a total pain in the ARSE to get rid of. I probably wound up heating the transistor too much in the process, but even with my heavier iron, it was really hard to get the solder enough to flow and get out of the bridge, even with lots of flux and fresh braid. I finally got it, but I think the damage was done at that point.

I don't SEEM to have shorts to ground or anything. One leg of course is connected to ground, so that's understood. Checking for shorts with the other legs, one has no reaction, the other shows continuity for about half a second, then it stops. That's on BOTH transistors, so if that's a sign of being blown, I blew 'em both. :/

IF, however, this sounds familiar, and I have some other issue going on, or anyone can think of some checks I can do with meter or wiggle scope, let me know what to check and to look for, and I'll try it and post back. I think I have some of those finals in my stock in case I need to replace them, but I want to narrow it down a bit before I go that route.

73,
Gwen, NG3P


George Korper
 

Allison had a great post on how to clear the hole after you snip the IR510 out,
Remove the leads, and heat the hole and tap quick on a table. Whamo the holes are like new. 
 Then start meticulously restoring the pads. 
And fuse the supply with a 4 amp fuse even if using a current limited supply. 
All that said look for the problem, but it may have actually been corrected in the process. 
It could be there was a problem in the mounting to the heat sink. That happened to me 4 TIMES!
Check that and don't tighten the screws too hard. 

On Thu, Apr 2, 2020 at 6:03 PM George Korper via groups.io <georgekorper=gmail.com@groups.io> wrote:
Ok this i have done. First after removing IR 510's you must clean the bridges in between the pads. 
I use M.G. Chemical solder braid # 452, but once you get a bridge between pads, it takes a magnifier and 
maybe an Exacto knife.You had to fry the finals and just go in there and bring everything back to where it was. 
You can check the transistors but the sad fact is it is easier to remove and go back to an initial condition than screw around. 
I have built quite a few and the last thing you want to do is rush and burn out all the traces. One slip and a cascade of trouble can happen so never probe around with the final in operation. Also bad finals can cause the problems you are seeing. The keying circuit can be
affected...not sure how but I've seen it. But check the keying circuit with a DVM any way.
And cool down, you'll find it. Take it easy but take it. Sometimes I just break em in half an order another one. 
Lately though they seem easy after the first half dozen. YOU ARE NOT ALONE!

On Thu, Apr 2, 2020 at 5:29 PM Gwen Patton <ardrhi@...> wrote:
Hey, All.

I finished building the QCX amp best I could, but I'm running into a serious issue, and think I MAY have fried one or both of the finals...or messed something else up, I'm not sure.

It powers up ok. No smoke. Nothing seems to be getting overly warm. With the QCX in practice mode and the keying line connected, when I key the QCX the red light comes on in time with the key. I did what the instructions say about adjusting the trimmer, and it seems to be okay. But when I take the QCX OUT of practice mode and try to key the amp, things get weird.

On the QCX, it seems fine for the space of two dahs. Then the letter "P" comes up to the left of the S-meter graphic (I know this is also on when in practice mode, but that mode is definitely OFF at this point) and the unit ceases transmitting. It takes a few seconds for the QCX screen to clear, then it will key up again, but once more, it's only very briefly, then it fails again, same thing.

I've tried THREE different power sources for the amp. I've tried it at 12v, I've tried it at 20v, no difference whatsoever. It just falls over a second or so after being keyed, and it doesn't seem to have anything to do with the QCX end or the power supply. So I'm pretty sure I munged something up in construction. Now, the reason I think I may have fried at least one of the final transistors is that I got a $^@#$ consarned solder bridge on one transistor's connections, and it was a total pain in the ARSE to get rid of. I probably wound up heating the transistor too much in the process, but even with my heavier iron, it was really hard to get the solder enough to flow and get out of the bridge, even with lots of flux and fresh braid. I finally got it, but I think the damage was done at that point.

I don't SEEM to have shorts to ground or anything. One leg of course is connected to ground, so that's understood. Checking for shorts with the other legs, one has no reaction, the other shows continuity for about half a second, then it stops. That's on BOTH transistors, so if that's a sign of being blown, I blew 'em both. :/

IF, however, this sounds familiar, and I have some other issue going on, or anyone can think of some checks I can do with meter or wiggle scope, let me know what to check and to look for, and I'll try it and post back. I think I have some of those finals in my stock in case I need to replace them, but I want to narrow it down a bit before I go that route.

73,
Gwen, NG3P


George Korper
 

Gwen, forgot one more thing. Always do this into a dummy load. The Amp cannot handle SWR of certain
types depending on the load. above 1.6 to 1 things get dicey.  Especially if the bias is set even a tad too high, 

On Thu, Apr 2, 2020 at 5:29 PM Gwen Patton <ardrhi@...> wrote:
Hey, All.

I finished building the QCX amp best I could, but I'm running into a serious issue, and think I MAY have fried one or both of the finals...or messed something else up, I'm not sure.

It powers up ok. No smoke. Nothing seems to be getting overly warm. With the QCX in practice mode and the keying line connected, when I key the QCX the red light comes on in time with the key. I did what the instructions say about adjusting the trimmer, and it seems to be okay. But when I take the QCX OUT of practice mode and try to key the amp, things get weird.

On the QCX, it seems fine for the space of two dahs. Then the letter "P" comes up to the left of the S-meter graphic (I know this is also on when in practice mode, but that mode is definitely OFF at this point) and the unit ceases transmitting. It takes a few seconds for the QCX screen to clear, then it will key up again, but once more, it's only very briefly, then it fails again, same thing.

I've tried THREE different power sources for the amp. I've tried it at 12v, I've tried it at 20v, no difference whatsoever. It just falls over a second or so after being keyed, and it doesn't seem to have anything to do with the QCX end or the power supply. So I'm pretty sure I munged something up in construction. Now, the reason I think I may have fried at least one of the final transistors is that I got a $^@#$ consarned solder bridge on one transistor's connections, and it was a total pain in the ARSE to get rid of. I probably wound up heating the transistor too much in the process, but even with my heavier iron, it was really hard to get the solder enough to flow and get out of the bridge, even with lots of flux and fresh braid. I finally got it, but I think the damage was done at that point.

I don't SEEM to have shorts to ground or anything. One leg of course is connected to ground, so that's understood. Checking for shorts with the other legs, one has no reaction, the other shows continuity for about half a second, then it stops. That's on BOTH transistors, so if that's a sign of being blown, I blew 'em both. :/

IF, however, this sounds familiar, and I have some other issue going on, or anyone can think of some checks I can do with meter or wiggle scope, let me know what to check and to look for, and I'll try it and post back. I think I have some of those finals in my stock in case I need to replace them, but I want to narrow it down a bit before I go that route.

73,
Gwen, NG3P


George Korper
 

But wait there's more: Not every IRF 510 works in the amp. So make sure you get them from 
a good house. Just pay shipping and handling, Hi Hi. 


George Korper
 

Hi, I don't mind going too far. There was one other thing I learned 
in the process. After you snug up the IRF 510 in the heatsink, cut the protruding leads
down before you solder. THEN FOLLOW THE PIN SOLDERING ORDER IN THE MANUAL
THAT HANS RECOMMENDS. RIGHT, CENTER, etc. Don't deviate because the fist pin takes a
long time not necessarily a big iron. With the lead cut down, you can get the heat into the hole and let it blossom around the pin. 
If you do that and scrape every transformer lead, tin it, and then  solder, everyone comes out perfect and consistent and is easy. 
Since doing the above two things I have made six without incident.