Neverending motor

[Calamaro]

I'm playing with a nice Philips cd210 that I've found (TDA1543 based). Made basic mods: nonoversampling and replaced opamps with LM4562. I really like the sound. So I wanted to add a dedicated 5v supply for the dac: cut the existing trace and connected the little pcb (input from main filter capacitor+capacitor+7805+capacitor) but when I switched on the player the motor started to run neverending! I really don't understand what happened, I think isn't a big problem but I'm not able to fix it.
Please really need help...
Thanks

 

[Calamaro]

I've replaced everything but when I switch on the player the motors still start to run. Maybe something in the SAA7310 chip?

 

[kevinkr]

Try removing the mod that caused this problem and see if the issue remains, if it does perhaps there is a bad chip or some other damage done as a result of the mod.

 

[philpoole]

Quite often, a ridiculously spinny motor is due to a lack of clock signal.
Maybe you've upset the power to the clock? or the decoder?

 

[martin clark]

Phil is right; you always need the clock to start before the decoder chip (the SAA7310 in this case) tries to take control of the disc servos.

Either undo the new-psu mod to the dac, or at least ensure this new PSU starts-up before the rest of the player. That might be as simple as juggling time-constants with the raw smoothing caps - smaller values for the DAC's supply, so it (and the attached clock) start first.

Incidentally, what dac does this player use..?

 

[Calamaro]

Thank you for your replies. Actually I didn't connect the new PS. This is the algorithm :
-cut the trace before the resistor that precedes the dac;
-connected a twisted pair wires to first filter capacitor pins;
-connected the other end of the twisted pair with new PS (capacitor+7805+capacitor)
-switched on the player (I wanted to check the voltage after regulator with a multimeter)
-SMOKE from the new PS
-ok, just an inverted capacitor (a little tantalum with invisible writing)
-replaced capacitor
-switched on the player: I don't remember if the motors started suddenly to run or if this happened a little later (anyway the player was reverted as I was working under the pcb: I don't know if this means something)
-PANIC
-tried to replace the cut trace with a little wire
-ok but the motors don't stop
-I really didn't understand
-I still don't understand

ps: Martin, the dac is a TDA1543 one.