| Author |
Message |
    
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 20
Registered: 6-2005
| | Posted on Monday, May 22, 2006 - 10:24 am: | 
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I was trying to jump my speaker switch and while testing I touched the audio wire on something and now I have no audio out and no speaker sound, just a clicking, sounds like a heartbeat.
Oh man.......what have I done ?
 |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 21
Registered: 6-2005
| | Posted on Monday, May 22, 2006 - 12:10 pm: |
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I just tried to replace c18 and its ok, am carier and receive needle move but audio is not present.... |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 23
Registered: 6-2005
| | Posted on Monday, May 22, 2006 - 1:09 pm: |
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ok I have audio on sideband but not am or receive ssb or am.
am has a light clicking or ticking that i can see move the needle on am, ssb seems to ok but not receive. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1663
Registered: 9-2004
| | Posted on Monday, May 22, 2006 - 5:45 pm: |
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just a guess, but you may have blown the audio IC,
its a cheap part, so it might be worth a try.
matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 25
Registered: 6-2005
| | Posted on Tuesday, May 23, 2006 - 2:42 am: |
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I hope someone knows EXCACTLY what is the problem.
Thanks for looking and thanks for the forum.
I really may need a nice padded cell after this.
Which is the audio chip ? |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 26
Registered: 6-2005
| | Posted on Tuesday, May 23, 2006 - 5:20 am: |
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OK I got the side off, ready to tackle the audio IC....
http://img95.imageshack.us/my.php?image=picture389ee.jpg
http://img164.imageshack.us/my.php?image=picture396uj.jpg |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 28
Registered: 6-2005
| | Posted on Tuesday, May 23, 2006 - 7:24 am: |
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OK, I took out TA7222AP
Is there a way to test if its good ?
thanks |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 30
Registered: 6-2005
| | Posted on Tuesday, May 23, 2006 - 8:10 am: |
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OK now I have a NEC C1156H
I compared impedance on the monting stub to pins 10 to 1
On my chip, there is no connection on any pin but pin 7
On the NEC chip there is a connection on most the pins.
So I HOPE it's only my audio chip and nothing else.
I was trying to eliminate a sqeal when the volume is maxed and or dynamike turned to max.
I never have either on full blast but why the squeal,? made me think I wired the speaker switch wires wrong.....thats when I touched the wrong wire and pop !
Will post results...
http://img301.imageshack.us/my.php?image=picture400pm.jpg
ALSO*
should I get the NTE1278 or an oringinal TA7222? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1675
Registered: 9-2004
| | Posted on Tuesday, May 23, 2006 - 7:02 pm: |
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if you dont own the test equipment to do the things suggested, then there is no point in trying to troubleshoot the problem that way.
if you do own the test equipment required to trace the problem down, then chances are you already know how to do it.
remember, its hard to say that this or that part is bad because one part going bad may cause a good one not to work.
power devices such as IC's and transistors are the most likely things to fail in a radio.
thats why we start there.
now, if you are going to replace the audio chip, why not replace all the electrolytic caps in the immediate area? they also dry up and go bad with age.
i replaced ALL the electrolytic caps in my 2000.
to me it was just easier than waiting for them to go bad one at a time and scratching my head about what went wrong.
cost about 20.00 for all the caps from mouser.
i dont understand what you mean about the NEC1156H
chip.
where did it come from?
are you trying to replace the TA7222 with it?
dont!
get the original chip.
dont forget the insulator and heatsink compound.
do you have a copy of "the screwdriver experts guide"?
if not, get one. it will really help you understand what you are doing.
PS-sent you a private message.
matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 38
Registered: 6-2005
| | Posted on Wednesday, May 24, 2006 - 9:17 am: |
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Ok Matt, thanks.
I got a digital Multimeter with diode tester so I can at least check them, which I did.
I usually get a good idea if the transistor is dead by seeing if theres any connection using the ohms measurement.
If there is some connection, I have a chance but if it remains at 0 at all pins, its a good gamble its dead, which is the case with the ta7222.
So I will replace the electolytic caps.
What caps should I soup up ?
I have a build sheet with the caps listed, would computer type low esr caps work ?
Is there a TA7222 bigblock ?
Thanks |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1685
Registered: 9-2004
| | Posted on Wednesday, May 24, 2006 - 5:41 pm: |
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i dont know what low ESR means, but as long as they are electrolytic capacitors, with the correct value in uF, and a suitable voltage rating, then they should be fine.
sorry, no upgrades for the TA7222. funny though!
the parts list is a great idea to order all the caps from.
when you come across a cap that is rated for 10 volts, replace it with one rated at 16 volts or more. (you could go as high as you want with voltage rating, but size beomes a problem)
you will find that some of the smaller cap values such as 1uF, or .47uF are only available in 50 volts or higher.
that just kind of works to your advantage.
so, no caps under 16 volt rated. OK?
the caps to upgrade to larger values are the ones in the files section under the heading:
"MB8719 dual conversion chassis upgrades"
dont change values just because you might think you need to. you might change very important characteristics of your radio.
BTW, you have to take the diodes out of the chassis to test them.
you cant test them while they are soldered to the board.
good luck,
matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 43
Registered: 6-2005
| | Posted on Thursday, May 25, 2006 - 6:32 pm: |
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OK thanks.
I need the TA7222 but I can only get a NTE1278.....is that ok?
Supposedly its a direct replacement, but I've heard that before...
Thanks Matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 47
Registered: 6-2005
| | Posted on Saturday, May 27, 2006 - 10:48 pm: |
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Well maybe I'll be the first to try it ?
Anyways I'll post my results and I took your advice and am gonna replace all the 10v caps with 16v, hope G-luxon is ok.....I heard bad reports but that's for computers, I can see that if someone used radio caps in a mobo to cut costs maybe that would give them a bad name.....hope they dont bulge |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1706
Registered: 9-2004
| | Posted on Saturday, May 27, 2006 - 10:53 pm: |
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i think computer parts have to be of a higher grade in general, so you should be ok.
sorry i havent been out here lately. work and all.
the NTE should be fine
matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 48
Registered: 6-2005
| | Posted on Sunday, May 28, 2006 - 1:46 pm: |
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As Rosco P. Coltrane would say, "GOOD NEWS, GOOD NEWS !!!"
I fixed it.
I replaced the 10v caps and the TA7222
http://img61.imageshack.us/my.php?image=picture354ce.jpg
http://img229.imageshack.us/my.php?image=picture361mo.jpg
http://img229.imageshack.us/my.php?image=picture400zr.jpg
heres the board prepared for the new chip
http://img61.imageshack.us/my.php?image=picture399it.jpg
Here's where I do my work
http://img229.imageshack.us/my.php?image=picture275go.jpg
So that's it in a nutshell, thaks to Copper electronics for the use of this forum, and Kid Vicious for his time and patience, and important tips.
The radio is now back to where it was, but I still get a squeal if I turn the mic gain all the way up, ON RECEIVE !
I dont know why it does it if I turn the gain 3\4 the way up it starts to make the sound change tone or become compressed ?
This time I wont try monkey-ing around with the audio wires till I find out the problem, other than that the radio works fine, thanks all !!
73's & 88's, 357 |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1712
Registered: 9-2004
| | Posted on Sunday, May 28, 2006 - 10:23 pm: |
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congratulations!!!
if i was of any help at all, im glad.
i cant think of what would be causing the squeal, but since the radio works, maybe its time to try some non electrical repairs.
get some good contact cleaner (DO NOT USE ANY OTHER PRODUCT SUCH AS WD-40!) you must use contact cleaner, and spray up inside the pots and switch assemblies using kleenexes to catch the overspray. (it can dull the finish on the meter plastic)
you will see a gap right near the solder terminals of the pots. spray the cleaner right ih there and turn the knob back and forth quickly until you feel it get easier.
same idea with the switches.
if you plan to replace all the elec. caps, you might just cure this problem.
does the squeal show up on an expternal speaker?
glad to hear that you can use the radio again,
good luck,
matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 49
Registered: 6-2005
| | Posted on Sunday, May 28, 2006 - 11:49 pm: |
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I'm a step ahead of ya Matt:
http://img226.imageshack.us/my.php?image=picture168ok.jpg
I can only imagine it's feedback, I just dont know why the dynamic mic control would cause a feedback on recieve.
I notice theres a transistor and diode on the switch pcb, I hope it's not part of the mic circut.
The aux record plug may have something to do with it since it has a connection to mic and speaker.
The owner before me put a switch in the aux plug, so I removed it and thankfully the unit was intact and taped out of the way.
I think I'll put TR24 back in too, I noticed my swing ain't as high on am now, maybe I'll retune the output section. |
