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Cbs1000 display contrast seems to have fallen out

Harley3315

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Oct 22, 2015
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The display contrast is almost completely gone unless your looking at it from the right angle you can't tell it
is on at all anyone else ever run across this?
 

Harley3315

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Oct 22, 2015
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Contrast on LCD is adjusted by voltage. It is too low for some reason.
That's what I was thinking I went and checked that choke on the display board that you tie to for the clarifier mod assuming there should be 8 volts there and only found about 2.5 volts
 

Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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There is a "buffer" resistor that Clarifier mod is used for - if you tie to the wrong side, - you suck all the power out of the controller voltage even for the display...

Might want to find another location or figure out a different tie point for that clarifier mod - it may be what is causing this.
 
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Harley3315

Active Member
Oct 22, 2015
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There is a "buffer" resistor that Clarifier mod is used for - if you tie to the wrong side, - you suck all the power out of the controller voltage even for the display...

Might want to find another location or figure out a different tie point for that clarifier mod - it may be what is causing this.
No I didn't tie to it at I used it a e reference point to see if the right voltage was there was all I expected 8 volt's it's no present only like 2.5 also noticed some heat on the transistor or 47ohm resistor in the far left corner of main board when I put my finger on the under side of the board. That would be q64 and r228 area
 

Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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These radios are pretty archaic - so if you can, try to find the "drop" from where the feedline to this trace goes - once it pops up to 8V - you're close to the spot - more than likely it is a bad cap, dried out electrolytic. That would be by the buffer resistor it feeds from (the LCD voltage branch)
 

Harley3315

Active Member
Oct 22, 2015
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These radios are pretty archaic - so if you can, try to find the "drop" from where the feedline to this trace goes - once it pops up to 8V - you're close to the spot - more than likely it is a bad cap, dried out electrolytic. That would be by the buffer resistor it feeds from (the LCD voltage branch)
Not really sure where the 8 volts start in to the face board from the main board that's the starting point I need
 

Harley3315

Active Member
Oct 22, 2015
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Not really sure where the 8 volts start in to the face board from the main board that's the starting point I need
Looking at the clarifier mod a wire goes to L204 not enough voltage there then looking at the parts list q64 isn't even mentioned that I saw assume maybe its part of the power supply section but unsure was trying to trace the 8 volts using the block diagram as well kinda didn't get anywhere.
 

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