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HELP!! low rf output on am and ssb ept3600-14b

S

smp440

Member
Sep 15, 2008
22
2
13
anyone please HELP!!!.
I have a superstar 3900 gold with dual final 3600-14b board. it used to swing big it has the npc and the clarifier unlock. I haven't used it for several years and hooked it up the other day. it used to put out 40 or soand now has a hard time to key 2w and swing 20 on am. Ssb is key 15w swing 20. None of the finals or am amp are getting worm and the schematic that I have has variences from my board some voltages don't mach but that may be from mods.
Sorry to get lng winded but wanted to get as much info as i could in. Din't know if some has seen this before. Thanks
 
Last edited:

thanks for your info, you were right using a d104, and shop fan on in background for ssb caused 15 dk. but can't get the power down evan test w/ 50ohm dummy load. mod used to swing hard because of npc mod but now truggles to get to 100% and no watt out on meter as stated. thanks again
 
I'd have it checked out by a reputable tech. It could just need a TX alignment, which should include checking the bias of the transistors. Or, it could be one of the finals or the driver that has failed.
 
thanks moleculo for the input.
any other thoughts.
What puzzles me is that nothing is heating up ie: tr49,50,51,44,45,43 and 56 nothing is getting evan remotely warm so i think its deeper then that. But not sure bucause voltage is off on ic4 and several test points and all the tr's ??? crazy. no one has a clue, other then (moleculo- thanks again)

P.S. anotherthing is evan though it is only at 20w it sounds very loud and clear to the people i get to.
 
I'm not looking at a schematic, so I can't tell you off the top of my head what IC4 is. But, if the voltages are all off, did you check what mods have been done to this rig? Maybe someone tried to volt the final and boogered it? You won't find anything out by trying to determine if it's warm. I would start by performing a complete TX alignment and checking the driver and finals. You kind've have to take the schematic and work backwards from the output to determine where the fault is (or work forward, I guess...your preference). Maybe the audio IC is the culprit?
 
ya, thats how i did start but after finding wrong voltages and not getting good voltage swing on tx, along with the fact that this problem is on am and ssb. I went up to the only other common circuit which is the ic4 where it all starts according to the block diagram. but you may be right... i may need to have a tech with all the correct tools look at it. i have not been making repairs for about 18yrs and only have a dvom and pwr meter.
I bought the radio new and the only mods done are the neg. peak and unlock clarifier. it worked for years after that... maybe its time to go new again... one of those 200w+ new boards
 
same meter that it showed 40w be for and tested it with a buddys meter same thing. then tried a rms meter and whistled into hold tone for a few seconds it got close to same. weird? but no not a meter issue.
 
Driver and final transsistors

I would think that you have either a bad driver and/or final. Since the problem is on SSB, that tells me that it is one or both. It may be that the final has failed, and since both the driver and the final are fed the same signal, the driver may be the only part putting out the power. The best way to find out what is going on without taking it to a shop is for you to remove the driver and final and check each to see if they are bad. If you are the type of person to experiment, it might pay you to purchase a transistor tester. Some DVMs have one built in, but you will need some small diameter wire to put down in the contacts in the meter, then some jumper leads to connect up to the leads on the transistors. You also have to know which leads are which on the transistors. Each transistor has different lead positions. Base, emitter, and collector, and you will need to know that to test the individual transistors. Don't assume that the leads on the transistors are the same. They may be, but chances are, that they are not. If you do decide to purchase the tester and remove the transistors, make sure you use a heat sink on each lead as you desolder it. If the transistor(s) are bad get new ones, and use the heatsink on each lead when you resolder them back in. Also, when you put the transistors back in, before you turn the set back on, check to see that you don't have a short between the transistor and the heat sink. Use your DVM on ohms to check that. Touch one lead to the tab or base lead on the transistor, and the other to the heatsink. Also, be careful when removing the screws on the transistors if they are plastic. The screws can be hard to find, especially if they are metric threads. Snug the screws down, but try not to snap them off. If the screwdriver starts to slip, that will probably be tight enough. MAKE SURE THE SET IS UNPLUGGED BEFORE WORKING ON IT.
 
Driver and final transsistors

I would think that you have either a bad driver and/or final. Since the problem is on SSB, that tells me that it is one or both. It may be that the final has failed, and since both the driver and the final are fed the same signal, the driver may be the only part putting out the power. The best way to find out what is going on without taking it to a shop is for you to remove the driver and final and check each to see if they are bad. If you are the type of person to experiment, it might pay you to purchase a transistor tester. Some DVMs have one built in, but you will need some small diameter wire to put down in the contacts in the meter, then some jumper leads to connect up to the leads on the transistors. You also have to know which leads are which on the transistors. Each transistor has different lead positions. Base, emitter, and collector, and you will need to know that to test the individual transistors. Don't assume that the leads on the transistors are the same. They may be, but chances are, that they are not. If you do decide to purchase the tester and remove the transistors, make sure you use a heat sink on each lead as you desolder it. If the transistor(s) are bad get new ones, and use the heatsink on each lead when you resolder them back in. Also, when you put the transistors back in, before you turn the set back on, check to see that you don't have a short between the transistor and the heat sink. Use your DVM on ohms to check that. Touch one lead to the tab or base lead on the transistor, and the other to the heatsink. Also, be careful when removing the screws on the transistors if they are plastic. The screws can be hard to find, especially if they are metric threads. Snug the screws down, but try not to snap them off. If the screwdriver starts to slip, that will probably be tight enough. MAKE SURE THE SET IS UNPLUGGED BEFORE WORKING ON IT.
 
Yah, it was the finals, Tx only driven by driver and a bad diode to realy screw me up on voltage. but the radio is back on track. thanks to all for your input.
 
smp440 said:
Yah, it was the finals, Tx only driven by driver and a bad diode to realy screw me up on voltage. but the radio is back on track. thanks to all for your input.
Click to expand...
Hi, I know that a lot of time has passed since this entry, could you indicate which diodes you found defective, I have the same low power problem, I replaced the final TX, and the problem persists
 
Hmm. A click on his avatar reveals his last visit in Sept 2015. Gotta figure you won't receive a prompt reply.

Infractor said:
I replaced the final TX, and the problem persists
Click to expand...
What kind of radio? And does it have one final and one driver transistor? Or one driver and two finals?

A way to test them is an enormous advantage. When a final is damaged enough to shut down your output power even a simple test tends to reveal a failure.

Do you have any measuring instruments, like a multimeter and a wattmeter on hand?

More tools often means less work. Not always, but often.

73
 
nomadradio said:
Hmm. A click on his avatar reveals his last visit in Sept 2015. Gotta figure you won't receive a prompt reply.


What kind of radio? And does it have one final and one driver transistor? Or one driver and two finals?

A way to test them is an enormous advantage. When a final is damaged enough to shut down your output power even a simple test tends to reveal a failure.

Do you have any measuring instruments, like a multimeter and a wattmeter on hand?

More tools often means less work. Not always, but often.

73
Click to expand...
 

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