Adcom GCD 600 spindle motor always on

hartbigsky

Member
2014-01-20 3:54 pm
I am trying to refurbish an Adcom GCD 600 [TDA1541A] I picked up cheaper than the chip set cost. The loader isn't working but when I put in on the bench and plugged it in the CD spindle motor started running before I powered it on?! I don't understand how it would get power as other functions clearly happen after AC is switched on. I know this is a vintage/nostalgia piece but does anyone know if this is normal for this unit??? Thanks for any ideas!

regards,
Steve
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
I'm not familiar with the player at all but what you describe doesn't sound normal.

First checks have to be all the rails, perhaps one is missing or perhaps a switched rail is staying on when it shouldn't.

Spinning motors can often be a sign of a PSU issue, or there could be a motor drive amp failure. Generally when a player is 'OFF' you'll find that (unless the switch is a mains on/off) that the player will be in standby and much of the circuitry could still be powered up.
 

hartbigsky

Member
2014-01-20 3:54 pm
So I just got hold of the service manual for this player. The electrolytic caps in the power supply seem to have the neg marked with a black dot. When I put a DMM to check polarity they seem to be only partially right! 2/3 have + pole in ground and that is how caps were in when I opened. Is the schematic just wrong. All my pin and header connections have ground as indicated as well as transistors [NPN/PNP] and +/- 15 voltage regs in supply. Should I just use ground to replace as they don't appear to be in series? If it was a short I would expect some + input be hot but I can't find one. Sorry my system fail is I power up system it blows fuses. Main transistors and V regs check OK [not shorted].Thanks for any ideas.

regards,
Steve
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Schematics can have odd single errors but that is all.

Its normal to have lots of caps fitted with + to ground... it simply means ground is more positive than the voltage that will be seen on the - lead of the cap.

Ground is just a reference point and voltages can and will be above and below this point.