Marantz cd94 mk1 power supply problem

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi.

I’ve just picked up a tatty cd94 mk1 that i am hoping to tweak over the coming months. (I can’t bring myself to modify the other ones that i have as they are in such good condition).

When a cd is inserted, the lens attempts to focus but the spindle does not start. The display then shows ERROR. I have replaced the notorious 33uf caps on the cdm, thinking that this might be the problem but this has not helped. I then proceeded to check all of the power supply rails. These all check out except for the neg 6 volt feed, which measures +0.755 volts. This appears to control the laser on/off from what i can see in the manual, so i assume that this is the problem.

I traced the rail back from the point of measurement (connector J802 on the lower LHS of the power/dac board) to the components that i assumed were at fault - D821, 6.8v zener; Q821, 2SA1358; C821, 220uf cap; and Q822, a 2SA1175. Interestingly Q822 is shown in the service manual as being a fuse, and not a transistor. All solder joints were old so i am sure that the parts were all original. Nevertheless, I have replaced these parts but the problem is still there.

I have also checked for dry or cracked solder joints on the power/dac board but can find none.

The player has an early non-A dac and i have been unable to find a circuit diagram that exactly matches. As i said above, there seem to be a few differences between the only circuit diagram i can find online and this machine. My other 1541A mk1 is slightly different to this one.

Can anybody offer any advice?
 
I have a MKII circuit diagram, but I could identify the components you mentioned. The -6V is derived from the -12V from Q831.
There are only a couple of components, but first I would check if there is no excessive load on the -6V. Cut the trace after C821 and check.
Check also -5V going to R824, and the voltage on D821 Zener diode (7.5V).
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.