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Message |
    
Af579
Junior Member
Username: Af579
Post Number: 29
Registered: 6-2003
| | Posted on Wednesday, March 23, 2005 - 4:55 pm: | 
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I have one in my shop that rx/tx great ssb. RX great AM but will not key on AM. any suggestions? |
1861
Intermediate Member
Username: 1861
Post Number: 126
Registered: 2-2004
| | Posted on Wednesday, March 23, 2005 - 6:17 pm: |
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I sure wish I did . I just shipped mine to my tech this morning . Does the exact same thing. If he calls and tells me what he found , I,ll post on here . |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 305
Registered: 9-2004
| | Posted on Wednesday, March 23, 2005 - 6:39 pm: |
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im gonna guess bad regulator IC. i dont know why, i just am!
matt |
Af579
Junior Member
Username: Af579
Post Number: 30
Registered: 6-2003
| | Posted on Saturday, March 26, 2005 - 11:06 pm: |
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any of the techs have an idea? |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 322
Registered: 9-2004
| | Posted on Sunday, March 27, 2005 - 12:38 am: |
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good luck getting a tech to take the time to answer this one.
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Tech808
Moderator
Username: Tech808
Post Number: 5350
Registered: 8-2002
| | Posted on Sunday, March 27, 2005 - 1:27 am: |
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Af579,
I have the Texas Ranger 696F SSB Base and never ran into this problem.
Sorry but I have never owned or used the mobile or know of anyone who has one.
Without having it on the bench and testing it, I would not even try and make a guess.
Lon
Tech808
CEF808
N9OSN |
2600
Advanced Member
Username: 2600
Post Number: 521
Registered: 7-2002
| | Posted on Monday, March 28, 2005 - 12:07 am: |
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You say it transmits on SSB.
Do you have an external meter in line with the radio?
If so, there are two possibilites:
1) You key the mike and the wattmeter reads ZERO on AM transmit, but kicks up nicely with mike audio on SSB.
2) You key the mike and the wattmeter slams, as high or (probably) higher than it does on SSB transmit.
If you have problem number 1, it's NOT a common failure that I see repeatedly. An o-scope is a really unfair advantage in any attempt to track down this one. Won't be easy without one.
If you have problem number 2, wattmeter shows power on AM, but nobody can hear you talk, that is a failed modulator/regulator transistor. Many of them do not have sufficient heat-conducting compound between the transistor, insulator and heat sink (chassis side rail). Causes it to fail prematurely. This one has the legend "Q54" printed on the pc board just in front of the part. It's bolted to the side rail at the right-rear of the radio, with its front facing you, turned upside-down, near the power socket.
There are numerous parts that will work as substitutes. If you have any 2SB754 on hand, that's what the factory uses.
Just make sure there is a good layer of compound on both sides of the insulator when the replacement goes in. So long as you see a thin bead of the compound squeeze out when the bolt is tightened, you have enough. All that's needed is a layer that will exclude air bubbles between the surfaces.
It's a good idea to also check Q55, the one directly in front of it. If Q54 fails, it can clobber Q55.
And if you don't have a way to check a transistor, this is too much like pin-the-tail-on the-donkey.
73
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