Sega CD Model 2 pot calibration values?

Hey,
I recently got a Sega CD unit, the model is the one with "Sony KSS-240A" laser. When I insert a disk and start it up the laser goes on but the motor never spins, from what I heard it could be a laser calibration issue and it does seem to have been fiddled with.

The problem is, this model has 3 different pots and tweaking it blindly is next to impossible, so my questions are:

1. Does anybody knows the values recommended to at least start from? I do have a multimeter and can measure resistance.
2. Any other tips? I don't know what to try next.

Thank you all for your time.
Ben

 

You DO NOT calibrate a laser by blindly tweaking pots. You DO NOT calibrate a laser by measuring the resistance of a pot.

Proper calibration of a laser diode is achieved with an oscilloscope, the correct test CD and the correct specifications from the service manual. If you can't achieve that, replace the mechanism.

 

I did it before on my Dreamcast without an Oscilloscope, it is possible if someone did it before me using the correct tools and measured the resistance. Even if the lasers aren't the same, at lease it will get me closer.

 

No, it is not. That is absurd.

That's like you telling me you bought a lovely pair of Nike shoes, best fit you've ever had. Then I ask you what size they were, as I want a good fitting pair of shoes. Just because they fit YOU doesn't mean they'll fit ME.

You adjust the focus and tracking gain of the laser. That will NOT have the same resistance on a pot every time. Consider having to raise a surface that has worn away. The thickness of a shim would vary depending on the amount of wear. You're raising the surface to a particular height, NOT just shoving the same size shim in as your friend used in his case.

 

x

 

Yes, I know this. I'll try to explain:
lets say we have 6 different lasers for 6 different consoles of 6 different people, and the voltage pot is set like this:

1. 950 ohms
2. 900 ohms
3. 1100 ohms
4. 1200 ohms
5. 750 ohms
6. 1000 ohms

Now, lets say the pot has a range of 0-4000 ohms. It is highly likely that the correct value for trial and error is somewhere between 750 and 1200 ohms, am I wrong? Mine could be set on 3500 ohms (for example) and I wouldn't know where to start.

I admit I'm not an expert in "Laser Science" but this is basic probability. It worked JUST FINE FOR THE DREAMCAST, got an initial position and tried it until I got the desired results...
Maybe this isn't the correct way to do this, but it is by no means absurd!

PS - I don't mean to sound ungrateful, I know you guys are just trying to help and I appreciate it

 

You are wrong, yes! (no offence intended, of course! Just saying that as a service engineer who has worked with CD players)

There is a measurement, but it's more complex than being a set resistance. If there was a set resistance, you wouldn't need a potentiometer!

In service manuals, you'll often find that you need to adjust a pot until a certain value is reached in a circuit... but it's never the resistance of the pot itself.

And some pots shouldn't be adjusted - don't adjust the output power. If you can't achieve the correct RF level, the diode needs replacing (essentially the whole pickup), or you could damage it.

It's not like, say, a CRT monitor where you have to adjust a pot to get the vertical hold steady. It's similar in that it's something that can drift as the item ages, but in that instance, you just twiddle it until you get a stable picture. This is a far more precise thing. The difference between a few hundred ohms could actually be a lot when it comes to the value you want to adjust. And if you're talking about the power pot, you shouldn't really be adjusting it... like I said, it's just delaying the inevitable and the pickup needs replacing. If it really is something that a curious person tweaked, I'd want it set to the correct value by the correct procedure, to maximize its lifespan, if it were mine.

Just because something might work as a temporary solution, doesn't mean it is the right thing to do. A friend of mine's Dad had a car that wouldn't start. Instead of getting it fixed, he kept a hammer in the car. My friend would get the hammer and hit the starter motor whilst his Dad turned the car over. It worked.... but it sure as hell isn't the right way to fix the problem, and didn't do it any good!

 

x

 

OK
I understand now and have ordered a new laser unit from Ebay.
Thank you all for your help!