Sanyo CDP-31 tracking alignment

laserguru

I have this Sanyo CDP-31 player that works with some discs but not with others.
When discs play, it is very sensitive to any shock, even skips from pressing some buttons, and from a dog barking too close! So clearly it needs a servo alignment.

With the discs that don't read, it spins and I can hear the focus coil "grinding", so I believe it is achieving focus, but is not tracking correctly.
I found the service manual for the CDP-4, although it only includes the schematic. Most of the circuit is the same. I have located the test points (tracking and focus output and error, PLL, and RF out) points, as well as all servo alignment potentiometers (TB, TG, FB, FG, PLL).
The next thing will be to look at the RF on the scope.
Any ideas on the alignment procedure for this player? Any help appreciated.

kaosun

If possible, connect a analog 40M oscilloscope to read the RF pattern. Adjust it to 1.2Vp-p with commercial discs; furthermore, adjusting TB and FB to make your RF biggest and cleanest. Your reading will be excellent.

laserguru

Thanks for the help, I will upload photo of the trace when I can. I adjusted and got the biggest signal I could get, it's mostly good, even when trying to read discs that won't play. What I found is that when there is no signal from the laser there is a big sine wave on the RF, about 0.3Vpp, about 3x the frequency of the RF. I can see this noise in the RF.
Time to check the DC-DC section and verify capacitors. Or perhaps replace them all? I thought they all measured OK but maybe I missed one.

kaosun

The 0.3Vp-p might be a bad ground connection. Caps over 47uf should be replaced one by one.