Fisher CA-800 Rebuild Thread!

I own the 880 but have never owned the 800 but from what I have read here, the only difference between the two is the 800 uses the extra circuit boards for the external voltage taps for the matching tuner and cassette tape deck. They look identical from the front.

From what is known, the tuner and cassette deck are not 120 volt and do not have conventional wall plugs so the 800 supplies the 15-24 (or whatever) volts it puts on the connectors in the rear.

The 880 does not have this option but it still uses the same STK-0080 amplifier blocks. Even though the meters say 100, the STK reference book I have says these 0080 amp blocks are only rated at 80 watts.

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at this point im almost sure the 800 was simply a cheaper version of the 880.
STK-0080's are rated at 80W at somithing like 0.02% THD. they will put out 100W but distortion starts to hit the 1% range then. if i could find it i would post it but i saw a guy on YouTube a while ago and he benched the STK-0080 at just a hair over 100W on 55V rails. Not Bad.
 
since the CA-800 has no adjustment for the LB1423 LED array, what bits can i change to make it less sensitive. the 5th light comes on around 10W. my original plan was to adjust it so the 5th light is half lit at 80W, untill i found out there is no adjustment on it.
Pin 8 on the LB1423 is the input and at first looks it appears by changing R35 R36 off of IC03 i can change the sensitivity.

EDIT: This could be a problem. looks like the LB gets its power from the AC off of the lights, so if i convert the lights to DC, i could have a problem here. i might be fine with removing C01 from the lever meter board.
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Lowering the value of R01, 22K, resistor should lessen the sensitivity of the circuit. R01 along with R35 and R36, 330K, form a voltage divider for the signal to the LED driver. Making R01 smaller should decrease the signal to the driver. Maybe replace R01 with a pot in series with a smaller resistor, combined resistance slightly more than 22K.

Craig
 
i might be able to completely remove R01 and replace it with a trimmer pot. 10K or 20K should be good. ill have to watch when i convert to DC power. dont want to power the IC backwards!
 
This LB1423 is throwing me off. it looks like the IC is powered from AC from the lights, and so are the 5 LED's?!??

To add adjustments to it what it looks like i can do is replace R01 22K for a 20K trimmer with wiper to ground in series with a 1K resistor.

to power the IC, what i think i have to do here is rewire the 5 LEDS to run from the other LED's when i convert them and power the IC from another source. maybe from the filter cap after the rectifier for the new LED's.:confused:

i threw together a pic of what it looks like i have to do here. does that look ok?
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Hmmm... the LED's have 9.3V on them...
well enough about the LB1423 for now...

I got the unit apart a little more to clean the dust out.
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This board should be easy to mod if need be. i want to swap those LED's out for a different color, they are normal rectangular LED's, thing is there only 1mm high and not the WAAYYY more common 2mm.
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5th light fully lit at (supposably) 10W.
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This LB1423 is throwing me off. it looks like the IC is powered from AC from the lights, and so are the 5 LED's?!??

i think the D06 makes it sort of DC, atleast enough to make things work
interesting that one side of the AC is hooked to GND :D
 
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i´d replace C01,C02,pre/tone section and C01,C02 in main amp section to some real quality caps. preferably MKT :)
there are 4more signal coupling caps in the preamp. C09,C10,C11,C12 if you want to go all in :)
 
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i think the D06 makes it sort of DC, atleast enough to make things work
interesting that one side of the AC is hooked to GND :D
sort of like a half wave bridge deal.
i´d replace C01,C02,pre/tone section and C01,C02 in main amp section to some real quality caps. preferably MKT :)
there are 4more signal coupling caps in the preamp. C09,C10,C11,C12 if you want to go all in :)
i could so that for preamp C01 C02 but the rest are 10uF and those aren't cheap. the ones i was looking at would be $21 for all 6! i think Nichicon KW will have to do here :(
 
im having trouble understanding that ac circuit....:) doesnt both ac lines connect to ground?
at post 4 and 5... i mean those 3 bulbs down there if i look at how they are hooked up i cant imagine them working.

yeah i know those mkts quickly get expensive!
or nichi UKL or Elna RFS are pretty ok.
guess its not the end of the world if u use something else :D
 
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Looks like wire 3-2 goes through the diode then a 100uF filter cap. seems pretty simple.
maybe the negitive side of the AC wave is on GND. that makes the most sense.
EDIT: i got a better idea for powering this, just hook up its AC signal to the transformer BEFORE the rectifier for the new LED's. Easy!
 
post 4 and 5 above the ind-light and meter lights both connect to ground. i cant see how that would work, i must be missing something
and the post 3-2 at the D06 leads to ground too only with a bulb between
 
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Well it works so i wouldn't try to get to wrapped up in it. Actually, isnt it the negitive side of the AC cord that goes to the chassis through a 3.9M ohm resistor?
 
I Don't need the trimmer for the LB1423 anymore, i was experimenting with my box of resistors and 9.5K is DAMN close to where i want it. I guess 9.2K would be spot on but i dont have a 9.2K ohm resistor :p
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That part of this build is taken care of.
 
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What i think im going to do for the LED's are make a regulated supply for them. because with a resistor the value will change depending on how many are lit. now, should i do linear, or switching?
 
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