First off, thank you all for the helpful technical info you have helped me with on a few other radios. I had to put the other radios you all helped me on up on the shelf for this rush job. God I hate being rushed.
Anyway,
Working on a connex cx3400hp dual mosfet ept360015c now.
Sent to me due to no transmit, carrier or modulation. I verified this and set it aside due to being backed up.
After further inspection, I noticed 2 small solder burs between the output voltage rail from the 2sb827 over to a 5v rail next to it. Obviously I checked the 2sb827 after seeing those burs and it showed as 2 diodes while in circuit, I then removed the burs and rechecked with same results. After I removed it, I noticed a hole and a crack in the face of the 827, so I replaced the 827 with tip36c (st micro brand), the1819 in front of it with a 2sa1012 and replaced all the mosfets (driver and both finals). I then double checked my work and then hooked everything up to test it. It keyed fine, modulated wimpy up to around 18 watts max. I then readjusted all bias' back to 3.70 volts for the driver and 3.50 volts each for the finals by using bare leads of L37, L50 and L35 to check. Got about 22 watts max from just the bias adjustments. I then proceeded to readjust L41, L42, L43 and L44 for max swing, could only get a max of 31 watts max. The mosfets ran cool the entire time I was keyed with modulation, (5 minutes at most) but the new power amp I replaced 827 with (tip36c) got pretty hot (the 2sa102's got pretty warm) so I shut it down and checked a few other things out. The whole time I was keyed, with modulation or not (mic gain up or down) there was this constant steady tone which sounded like a 900hz going with the carrier, modulation would cover it up. Upon checking a few other things, I found that the biasing diodes (strapped across each individual mosfet) were all showing OPEN, even my parts tester said it was a "bad part or no part plugged in".
I am taking a break from it for tonight, but I am curious of a few things:
Would those bias diodes being bad make that tone on a carrier?
Would those bias diodes make the tip36c get hot?
Would those bias diodes affect the wattage that much?
Note:
This radio has had only 3 mods to it that I know of.
A talkback mod consisting of an electrolytic cap, disc cap and diode on the trace side of the board near the tip36c, AMC removed, 2 diodes tied together at the D79 and D65 locations, and maybe another mod from a brown wire soldered to the bare side (top side of board) of R205 (part of a channel mod maybe). Nothing clipped other than the AMC removed. Nothing looks burnt, visually internally it looks brand new, no visual signs of burnt or overheated resistors or caps, no burnt traces, everything else in the radio runs very cool, just the tip36c gets very hot, the 2 2sa1012's get warm, strange tone on carrier, lights do not dim whatsoever when keyed or modulated.
The owner stated he stopped at a truck stop and had them mod it. He stated it ran fine for a week or so and then stopped transmitting, so he dropped it off at a different truck stop and they charged him for new mosfets and tune. He said it worked fine for a week and then smoke came out the back corner where your DC plug is. He said he got frustrated and just threw it in his closet. Now he's heavy into radio and wants me to straighten it out for him. I informed him of the damage and the cost just to get to the starting point of just being able to transmit, then we may run into more money and time, he doesn't care, he wants this radio fixed, I think it had some sentimental value to him.
Anyway, any help would be greatly appreciated as I'm not charging labor on this radio, just the price of the parts to help the guy out because I've had this radio on the shelf for a couple months.
Sorry so lengthy, but you get more detailed advice when you give more detailed information.
Thanks in advance...
Anyway,
Working on a connex cx3400hp dual mosfet ept360015c now.
Sent to me due to no transmit, carrier or modulation. I verified this and set it aside due to being backed up.
After further inspection, I noticed 2 small solder burs between the output voltage rail from the 2sb827 over to a 5v rail next to it. Obviously I checked the 2sb827 after seeing those burs and it showed as 2 diodes while in circuit, I then removed the burs and rechecked with same results. After I removed it, I noticed a hole and a crack in the face of the 827, so I replaced the 827 with tip36c (st micro brand), the1819 in front of it with a 2sa1012 and replaced all the mosfets (driver and both finals). I then double checked my work and then hooked everything up to test it. It keyed fine, modulated wimpy up to around 18 watts max. I then readjusted all bias' back to 3.70 volts for the driver and 3.50 volts each for the finals by using bare leads of L37, L50 and L35 to check. Got about 22 watts max from just the bias adjustments. I then proceeded to readjust L41, L42, L43 and L44 for max swing, could only get a max of 31 watts max. The mosfets ran cool the entire time I was keyed with modulation, (5 minutes at most) but the new power amp I replaced 827 with (tip36c) got pretty hot (the 2sa102's got pretty warm) so I shut it down and checked a few other things out. The whole time I was keyed, with modulation or not (mic gain up or down) there was this constant steady tone which sounded like a 900hz going with the carrier, modulation would cover it up. Upon checking a few other things, I found that the biasing diodes (strapped across each individual mosfet) were all showing OPEN, even my parts tester said it was a "bad part or no part plugged in".
I am taking a break from it for tonight, but I am curious of a few things:
Would those bias diodes being bad make that tone on a carrier?
Would those bias diodes make the tip36c get hot?
Would those bias diodes affect the wattage that much?
Note:
This radio has had only 3 mods to it that I know of.
A talkback mod consisting of an electrolytic cap, disc cap and diode on the trace side of the board near the tip36c, AMC removed, 2 diodes tied together at the D79 and D65 locations, and maybe another mod from a brown wire soldered to the bare side (top side of board) of R205 (part of a channel mod maybe). Nothing clipped other than the AMC removed. Nothing looks burnt, visually internally it looks brand new, no visual signs of burnt or overheated resistors or caps, no burnt traces, everything else in the radio runs very cool, just the tip36c gets very hot, the 2 2sa1012's get warm, strange tone on carrier, lights do not dim whatsoever when keyed or modulated.
The owner stated he stopped at a truck stop and had them mod it. He stated it ran fine for a week or so and then stopped transmitting, so he dropped it off at a different truck stop and they charged him for new mosfets and tune. He said it worked fine for a week and then smoke came out the back corner where your DC plug is. He said he got frustrated and just threw it in his closet. Now he's heavy into radio and wants me to straighten it out for him. I informed him of the damage and the cost just to get to the starting point of just being able to transmit, then we may run into more money and time, he doesn't care, he wants this radio fixed, I think it had some sentimental value to him.
Anyway, any help would be greatly appreciated as I'm not charging labor on this radio, just the price of the parts to help the guy out because I've had this radio on the shelf for a couple months.
Sorry so lengthy, but you get more detailed advice when you give more detailed information.
Thanks in advance...