Cbs1000 display contrast seems to have fallen out

[Harley3315]

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?

 

[sp5it]

Contrast on LCD is adjusted by voltage. It is too low for some reason.

 

[Harley3315]

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]

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.

 

[Harley3315]

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]

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]

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]

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.