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Message |
    
Supernuker
New member
Username: Supernuker
Post Number: 2
Registered: 11-2004
| | Posted on Wednesday, November 17, 2004 - 12:18 am: | 
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This radio lights up but won't do much more. It's a Thailand version from I don't know what year. There's no RX, no TX but the light on the front changes to red when keyed. No power out, no audio out on PA either. What a mess. The meter lights up but never moves - I don't think it's stuck though. The channel indicator works properly. The ST led lights up when ST button is pushed.
Could all this be caused by a faulty IC1 MB-8719 PLL? Someone has applied a frequency mod here and I'm only guessing it got screwed up. Would that cause no TX though?
Grrr, I'd like to get this radio back on it's feet. I'm hoping it's something relatively simple. I have just about every piece of test equipment needed - Dig Scope, Multimeter, RF Generator, Audio Generator, dummy load, freq counter.
Thanks in advance. I'll post my results as I go here. |
Supernuker
New member
Username: Supernuker
Post Number: 3
Registered: 11-2004
| | Posted on Wednesday, November 17, 2004 - 3:29 pm: |
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Actually, now that I'm looking at the block diagram, I think the problem is in the ST module. The SoundTracker deals with TX MOD IN, RX AUD OUT, TX MOD OUT, and PA. Everything I described as a problem above.
There's two chips on this module that I'll look at, but it's probably IC2 4066PA or related circuitry.
More later. |
Supernuker
New member
Username: Supernuker
Post Number: 4
Registered: 11-2004
| | Posted on Wednesday, November 17, 2004 - 7:53 pm: |
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I've now checked out the ST module, it checks out. Proper voltages to two IC's and two transistors.
I'll try to track down one problem at a time. Either TX, RX, or PA, whatever. Nothing inside appears blown, or burnt, or missing, etc. I hope this radio isn't lost.
Anyone come up against this problem?
Later... |
Supernuker
New member
Username: Supernuker
Post Number: 5
Registered: 11-2004
| | Posted on Thursday, November 18, 2004 - 6:44 pm: |
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Ok, it's back to the PLL. I'm not getting the 10.240MHz from pins 7,8. This could mean the crystal is out but the PLL is more likely.
I'm going to have to track down an MB8719. I think I can get an RCI8719...will this work in it's place? |
Supernuker
Junior Member
Username: Supernuker
Post Number: 10
Registered: 11-2004
| | Posted on Friday, December 03, 2004 - 8:28 am: |
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I've installed a new PLL MB8719 in this radio. It smoked R130 (10ohm) and a 1000uF electrolytic coming off the supply voltage pin (9) to the PLL chip. Why would the PLL be drawing so much current? I'm going to try to isolate the circuit today. |
Supernuker
Junior Member
Username: Supernuker
Post Number: 14
Registered: 11-2004
| | Posted on Friday, December 24, 2004 - 4:04 pm: |
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I think I finally got the PLL circuit worked out but now the finals seem bad too. I'm waiting for new finals to arrive, then I think I'm home free...I hope. It's a good thing I got this radio for nothing - it's cost me about $75 in parts and shipping so far. Alas, it's a hobby. |
Supernuker
Junior Member
Username: Supernuker
Post Number: 26
Registered: 11-2004
| | Posted on Tuesday, February 08, 2005 - 3:41 pm: |
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Installed the finals and now it puts out 4 Watts Am and roughly 12 Watts SSB. It's still off frequency though. I thought I had the PLL all worked out, but now it's something else. I guess it's possible to get a bad 'new' PLL chip.
Still trying...
CEF459 out. |
