I've heard mixed comments on biasing opamps into class A. Some say that it shouldn't make any difference either because they're pretty much in class A anyway due to the low levels involved (we're not swinging between power rails here), or that the crossover distortion is minimised due to the feedback involved.
Likewise, others seem to swear by it.
Definitely one to investigate.
Cheers,
Phil
Likewise, others seem to swear by it.
Definitely one to investigate.
Cheers,
Phil
Just curious if anyone else has had QM01 failure
I was listening to my mildly moded CD63SE the other night and it started messing up. Before I knew it, the spindle motor has spun up to like 40x the normal speed and the disc was starting to make grinding noises. I shut it off immediately. Tryed a few things, service mode, unplugging, etc. The problem was not going away.
So, the next day, I disected it and started troubleshooting. I found that both the spindle motor and the tray motor were both spinning out of control no matter what state the player was in.
Tracing the service manual and checking voltages, I found the problem to be around the motor control op-amp (QMO1). It appears that the IC is shorted and negagive voltage is streaming across and mucking up the whole circuit. The chip is a TCA0372DP2 which is made by ON semiconductor (formerly Motorola). I couldn't find replacements from any of the usual part stores, so I ended up ordering straight from ON. I have no idea how long it will take to get the parts.
I was just wondering if anybody else has ever had this problem?
I was listening to my mildly moded CD63SE the other night and it started messing up. Before I knew it, the spindle motor has spun up to like 40x the normal speed and the disc was starting to make grinding noises. I shut it off immediately. Tryed a few things, service mode, unplugging, etc. The problem was not going away.
So, the next day, I disected it and started troubleshooting. I found that both the spindle motor and the tray motor were both spinning out of control no matter what state the player was in.
Tracing the service manual and checking voltages, I found the problem to be around the motor control op-amp (QMO1). It appears that the IC is shorted and negagive voltage is streaming across and mucking up the whole circuit. The chip is a TCA0372DP2 which is made by ON semiconductor (formerly Motorola). I couldn't find replacements from any of the usual part stores, so I ended up ordering straight from ON. I have no idea how long it will take to get the parts.
I was just wondering if anybody else has ever had this problem?
Re: Just curious if anyone else has had QM01 failure
Nope.. lol
I have worked on a lot of these and other machines with that chip in and have never had that problem. They are usually super reliable.
Unlucky.
Take the chip out and make sure all voltage rails are ok. Then a new chip should cure the probs.
billbillw said:
Nope.. lol
I have worked on a lot of these and other machines with that chip in and have never had that problem. They are usually super reliable.
Unlucky.
Take the chip out and make sure all voltage rails are ok. Then a new chip should cure the probs.
Before unsoldering anything just check your clock connections if you are using one. The disc motor spinning up out of control is usually a sign that the decoder (SAA--- chip) is not getting the clock signal (so motor output drifts to one pole or another) or the clock is starting up late (slow ramp-up on power supply is frequent suspect), with the same effect.
The clock need to start up early after switch on to avoid this - so massive filtering /long time constants in its supply can cause problems, too.
HTH.
The clock need to start up early after switch on to avoid this - so massive filtering /long time constants in its supply can cause problems, too.
HTH.
