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Message |
    
Bullfrog13x4
Junior Member
Username: Bullfrog13x4
Post Number: 24
Registered: 3-2006
| | Posted on Wednesday, April 19, 2006 - 1:18 am: | 
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a friend of mune brought to me a 2000 that has been hacked on and after replacing many parts and all of the 10volt caps i can not get either side band to work properly, i can get the am and ssb freq's all lighned up perfectly rec and trx and am works great butt no matter what i try the ssb audio sounds over driven like a low dead key sound. any ideas what might cause this?
bullfrog13x4 |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1454
Registered: 9-2004
| | Posted on Wednesday, April 19, 2006 - 4:53 pm: |
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check VR4. its the carrier balance.
if misadjusted, it will cause a carrier on SSB.
to adjust it; connect a wattmeter to the radio, and set it on its lowest scale. (0-10, or 0-20 etc...)
turn the mic gain on the radio all the way down, and key the mic on either LSB or USB.
if you see ANY movement from the wattmeter needle, adjust VR4 so that when you key the mic, the needle doesnt move AT ALL. (you are adjusting for a "null")
check both sidebands to make sure its the same for both. (it probably will be)
this should do it.
also, look near VR11 for a cut or removed transistor, if you think you find one, tell me the part number. i cant remember it right now.
you will want to replace it.
also back VR11 down to 3/4 if it is all the way up.
if this doesnt work, we'll try biasing the driver and final.
matt |
Bullfrog13x4
Junior Member
Username: Bullfrog13x4
Post Number: 25
Registered: 3-2006
| | Posted on Thursday, April 20, 2006 - 1:53 am: |
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the ssb ballance has already been set, and as i said the radio apears to tune in properly on the bench everything looks right butt the guys 10 miles out say it sounds like i am over driving an amp. there is just a wierd noise with my modulation not any rf dead key? this apears in ssb mode only?????????
what would be the best method of biasing the driver and final????? resistor+cap like a linear?? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1464
Registered: 9-2004
| | Posted on Thursday, April 20, 2006 - 7:23 pm: |
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to bias the driver and final, look near them, and you will see a wire coming from the PC board in front of each one. (probably yellow purple or green)
follow these wires to their far ends and you will see that they will pull off of the connector there.
carefully pull the wire in front of the driver out, and insert your DC milliamps meter in line with it.
(if the meter reads negative, switch the positive and negative leads around) remember, you are measuring for CURRENT, not voltage, and the test lead configuration is different.
adjust the VR in front of the driver for 30mA.
repeat this process for the final, and adjust it for 60mA.
if this doesnt work well, try 25 and 50mA.
its the ratio thats critical.
also, what mods have been done to this radio?
by you?
history?
matt |
Bullfrog13x4
Junior Member
Username: Bullfrog13x4
Post Number: 27
Registered: 3-2006
| | Posted on Friday, April 21, 2006 - 2:00 am: |
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it has had variable power added to it with a tap directly off of the power vr and a low power vr as well. it is basicly installed in place of the origonal vr it is just external with limit adjustments internal.
i have upgraded the driver and final to 2166/2312 pnp n.o.s. parts and the power reg. to 1135. it has the popular band switch with 10k added as well. the clarifier it intact as factory or still locked. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1471
Registered: 9-2004
| | Posted on Saturday, April 22, 2006 - 10:08 pm: |
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what do you mean by "low power VR as well"? i didnt get that part.
i would say that the final upgrade is the first place to look for your problem.
i know they are basically interchangeable parts, but they may be different enough to cause problems in your application.
the bias definitely needs to be reset if you replaced the final and driver.
you need to do this first.
i like the NTE152 or NTE291 better as a replacement than the 1135. hitgher amp rating.
there is another one on the power supply board to replace.
if for some reason the power supply is not putting out enough amps, then you might not notice it on AM, but you would definitely hear distortion on SSB.
the transmitter is starving for power.
try running the radio off of an external power supply of 5 amps or more, and see if this cures the problem.
if so, you have power suppy issues, and should replace the main filter cap (underside of radio)
and the regulator on the PS board.
good luck,
bias that final and driver, and try the ext. power supply first.
matt |
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