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Lasonic stereo tuner issue...


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#1 Jovie

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Posted 03 March 2010 - 06:06 PM

My awesome Lasonic LPC-990 3 piece gets FM stations in only mono.They amber indicator on the tuning marker will at times blip red,but will never hold a stereo tune.Some time ago I heard that there was a screw adjustment for this on tuner boards.However,I am not sure where this might be located.Below are pictures of the 990's tuning board.The top picture shows it from its topside.The picture below shows the board from its underside on the big wheels end of it.I can see a number of pieces with screw slots on them but I'm not sure which of these might do the trick.Has anyone an idea?

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#2 monchito

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Posted 03 March 2010 - 08:42 PM

i belive its the pot sr1 thats next to that la3361 am/fm multiplex chip :-)

#3 Superduper

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Posted 03 March 2010 - 09:14 PM

:agree:

To be more specific, pin 8 of that LA3361 IC will lead to a trimpot that will adjust separation. Pin 16 will go through 1 resistor, then to another trimpot that will adjust the 19khz adjustment. This is the trimpot to adjust the Stereo. To identify the pins, pin 1 will be to the left of the notch on the IC, and pin 8 will be on the same row, down to the end of the IC. Pin 16 will be on the right of the notch.

#4 MasterBlaster84

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Posted 03 March 2010 - 09:18 PM

Come on SD can't you describe this for Jovie in a little more detail. :hmmm: :lol: :bow: :bow:

#5 Jovie

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Posted 03 March 2010 - 09:57 PM

WOW! You guys are good :jawdrop: ! ...Now for the newbie questions :blush: I'm assuming that I should turn SR1 while trying to tune a station with the tuner dial....which way?...clockwise,perhaps?...with what?...small screwdriver?...does one just stop adjustment when the indicator stays red?

#6 monchito

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Posted 03 March 2010 - 10:18 PM

pick a good strong signal make sure you are in stereo mode and you really do not need to turn it much it should light up if not then there may be more to that then just the adjustment but most of the time just turning the pot a bit should work :-)

#7 monchito

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Posted 03 March 2010 - 10:21 PM

WOW! You guys are good :jawdrop: ! ...Now for the newbie questions :blush: I'm assuming that I should turn SR1 while trying to tune a station with the tuner dial....which way?...clockwise,perhaps?...with what?...small screwdriver?...does one just stop adjustment when the indicator stays red?

yes jovie a small screwdriver and once the light comes on thats it .......

#8 Superduper

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Posted 03 March 2010 - 10:47 PM

Ok. Like Ramon said, tune to a good stereo channel. Then turn the trimpot one way or next until the indicator lights. However, there is a range where the indicator will light. Try to find the midpoint between the two extremes where the light extinguishes. That should be the centerpoint. If you set the trimpot where the indicator just lights, you may be at the extreme edge of the setting and on a strong station, no problem. On a weak station, you may have trouble capturing the stereo signal. That's why you'll want to be at the midpoint.

#9 Superduper

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Posted 03 March 2010 - 11:03 PM

Come on SD can't you describe this for Jovie in a little more detail. :hmmm: :lol: :bow: :bow:


Yeah, see the thing is, there are probably more than 1 trimpots in his PCB and if Jovie here were to start spinning the wrong one and throws his tuner out of wack, then he'd be mad at me (although I'd blame it on Ramon since I'm just following his lead here). Then there is the unobtanium service manual issue. Bottom line -- screw up this tuner and it might not be fixable. :w00t: :-O

#10 Johnny

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Posted 03 March 2010 - 11:17 PM

Come on SD can't you describe this for Jovie in a little more detail. :hmmm: :lol: :bow: :bow:


Yeah, see the thing is, there are probably more than 1 trimpots in his PCB and if Jovie here were to start spinning the wrong one and throws his tuner out of wack, then he'd be mad at me (although I'd blame it on Ramon since I'm just following his lead here). Then there is the unobtanium service manual issue. Bottom line -- screw up this tuner and it might not be fixable. :w00t: :-O



You could fix it :yes: :stereo:

#11 Jovie

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Posted 04 March 2010 - 11:17 AM

well...I tuned to a station with the unit open,fine tuned SR1 and absolutely nothing happens.Still mono,marker light remains amber despite turning the piece to each extreme position,and everywhere in between.....any other ideas?Perhaps LA 3361 IC is just bad or something.Might a replacement be available?

#12 MasterBlaster84

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Posted 04 March 2010 - 11:21 AM

Then there is the unobtanium service manual issue. Bottom line -- screw up this tuner and it might not be fixable. :w00t: :-O


I really hate these unobtanium service manuals. Come on Lasonic you pumped hundreds of thousands of boxes or more, can't you spit out the service manual?

#13 Superduper

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Posted 04 March 2010 - 01:00 PM

well...I tuned to a station with the unit open,fine tuned SR1 and absolutely nothing happens.Still mono,marker light remains amber despite turning the piece to each extreme position,and everywhere in between.....any other ideas?Perhaps LA 3361 IC is just bad or something.Might a replacement be available?


:yes: That would be the next step IF that trim pot is testing good (it could be bad). The main function of the Sanyo LA 3361 module is, after all, to decode multiplex (stereo) signals. If your soldering skills aren't that good, you may want to solder an IC socket onto the PCB first, then plug the new replacement IC into the socket to prevent heat stress damage to the new module. Also, are you sure it isn't capturing stereo but that your LED is bad?

#14 Jovie

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Posted 04 March 2010 - 03:06 PM

No stereo output to the speakers I'm sure.Actually,I have a friend who is OK at soldering.I'm wanting to get into this but I'm still working on a space to set up shop.Is it possible to get a new trim pot and put that in to eliminate that possible failure?They shouldn't cost much.Otherwise,how are these pieces "tested"?Are the LA 3361 ICs readily available?I'm sure my friend could,at least,solder on a new IC socket as you suggest if these ICs are obtainable.Do they still make these or would I find one used?

#15 Superduper

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Posted 04 March 2010 - 05:50 PM

If you can't get the Sanyo chip, you can get the generic NTE replacement, which is NTE# 1248. Don't replace the trimpot without testing it first. Just use a DMM and make sure that you are #1 getting continuity and #2 that the value read varies with the trimpot position. That will confirm that it's working. Typically when they fail, they fail open.

#16 Jovie

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Posted 05 March 2010 - 04:01 AM

thanks all for your replies :-) and for your continued attention and support Superduper :yes: .I'm confident I can solve this problem now with some help of a friend locally.

For the record,this model sounds amazing and is an amazing box! Mine seemed as if it had only single full range drivers until I recapped the tweeters.Wow :w00t: ,what a difference! The LPC-990 is easy to get into and work on. I had to put a deck in it from a trashed 975.I'm hoping to get my example fully functional by handling this stereo FM issue.There's one on Ebay currently but it has a very high starting bid requirement.Though not as pristine,mine only cost $9.95 from a thrifty a couple of years ago.Again,Thanks for everything :-D .

#17 monchito

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Posted 05 March 2010 - 04:43 AM

If you can't get the Sanyo chip, you can get the generic NTE replacement, which is NTE# 1248. Don't replace the trimpot without testing it first. Just use a DMM and make sure that you are #1 getting continuity and #2 that the value read varies with the trimpot position. That will confirm that it's working. Typically when they fail, they fail open.

:agree: :agree: :agree: :agree: