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Message |
    
Orange_peel
New member
Username: Orange_peel
Post Number: 1
Registered: 10-2014
| | Posted on Monday, October 13, 2014 - 11:07 am: | 
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hello to all, here is my problem with this radio, when you turn up the volume it starts to howl at about the 12 O clock position, rx is good and tx is good. I tried using differnt mics, but still has the howl, if I use my mic test plug, with just #3 and #4 pins jumped the howl is gone, I wired up my old yaesu md1 with #1 audio #2 shld #5tx and 3&4 jumped, the howl stops and have full volume, but now it has talk back and low audio output. And yes audio limiter has been long gone, I just got this so have no idea how much has been modded. Dead key 4w and swings to 15w. upper and lower 20w. Help |
Orange_peel
New member
Username: Orange_peel
Post Number: 2
Registered: 10-2014
| | Posted on Thursday, October 16, 2014 - 5:22 pm: |
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Ok, I have removed the 10volt blues, with 35volters, and rechecked radio and still has the howling thru any speaker int/ext. I reinstalled the missing tr32, I pulled c113 the fb filter and was fine. I have started ordering all new 2sc945 and 2sa733, I will start changing out one at a time.!! |
Dale
Senior Member
Username: Dale
Post Number: 2123
Registered: 12-2002
| | Posted on Friday, October 17, 2014 - 8:25 pm: |
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reinstalling tr32 and other limiters would been
my FIRST suggestion.second i know you tried different mic but did you try a noise canselling mic?all else seems normal hopefully someone else will chime in. try using those mic adapters from coppers they solve alot of mic wiring issues
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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Orange_peel
New member
Username: Orange_peel
Post Number: 3
Registered: 10-2014
| | Posted on Saturday, October 18, 2014 - 12:25 pm: |
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Dale, It's not a mic problem. If you have no mic plugged in and you jump pins 2 and 3 on the mic jack the radio howls when you turn up the volume just past 1/2 way, but if you jump pins 3 and 4 it does not howl, I have no more test gear so I can't check much, but I'm still thinking shorted diodes and or transistors, maybe tr13 or tr30?. I do know this radio mother board has gone thru hell what a mess, they removed mb3756 and installed a relay in it's place, this is all due to ruining the board traces, and as I said it does receive and transmit you just can't turn up the volume too far with out it howling, the more you turn it up the higher pitch in the howl. |
Dale
Senior Member
Username: Dale
Post Number: 2125
Registered: 12-2002
| | Posted on Sunday, October 19, 2014 - 10:20 am: |
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with a cobra 142 you unplug any mic from it
you shouldnt hear anything at all.did ya check
the plug itself
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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Orange_peel
New member
Username: Orange_peel
Post Number: 4
Registered: 10-2014
| | Posted on Monday, October 20, 2014 - 8:16 pm: |
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yes plug/jack are fine, and yes without mic plugged in, there is no sound. To test audio receive I jumped pin 2 and 3 on radio, and have receive but has very bad howl when turning up volume control past 1/2 way, with or without any mics. I checked received with my heathkit signal generator and had good signal, but still had the howl, and close by people can just be heard, where as dx station blast in with volume down low, I'm thinking of changing out tr9 with a 2sc2999 and diodes 1 and 2 along with 21 and 22, I have replaced all of the electrolytic caps and all of the 2sc945's, I will change all the 2sa733 while I'm doing nothing, may change out ta7222ap just for grins and giggles, I'm going to get to the bottom of this howling problem even if I have to replace every thing on this board! |
Orange_peel
New member
Username: Orange_peel
Post Number: 5
Registered: 10-2014
| | Posted on Tuesday, October 21, 2014 - 3:45 pm: |
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I need a good picture of the bottom of the board around the mb3756 (ic5) area, so maybe can repair all the traces that someone has destroyed from too much heat, I'm sure this is a lot of the receive audio problem. Thanks for any help on this |
Press_man
Advanced Member
Username: Press_man
Post Number: 804
Registered: 5-2008
| | Posted on Wednesday, October 22, 2014 - 6:30 pm: |
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I have a few 385 chassis radios and all of them howled. I switched the desk mic to a little black Cobra mic and it cured them. On the mobiles I used a Hand held D-104. Seemed the main thing was each of them wanted low impedance.
73 Pressman
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