Mac Classic analog board problem

[honza]

Hi!

I've just acquired an old Macintosh Classic. It is U.S. version with 110V power supply. I found out that someone probably tried to connect them to 230V because the fuse is broken and one (probably switching) transistor explode.

I would like to repair it but i don't know what type of transistor is used. It is marked as QP2 on PCB, type of board is 630-0525-8. Do somebody know type of QP2 transistor? Or do you have a scheme of power supply?

Thank you very much!

Honza

 

[Mac128]

The Classic has a universal power supply. If jumper JP1 is in place, it is 110V. If it is removed, it is 220V. Obviously someone failed to remove it.

Q2 is a BU406 transistor in both the Plus and the SE series. Since these are equivalent machines as far as the analogue board goes, I would assume something similar, if not the same on the Classic. My QP2 looks identical to the Q2 transistor on my Classic. Has yours exploded to the point you cannot read the markings on yours? If so, then it's a matter for someone to disassemble their Classic enough to read QP2.

 

[honza]

Has yours exploded to the point you cannot read the markings on yours?

Yes, almost half of its package (with all markings)is missing

Anyway I replaced QP2 for new BU406, removed JP1, replaced blown fuse and connected to 230V and tried to switch on but nothing happened Fuse stay intact now. I still have no diagram for analog board but I noticed that QP2 is driven by some analog IC... I will try to replace also that IC.

Thanks!

 

[bajin]

Hi, I just bought Mac Classic and I have the same problem with analog board as Honza has.The QP2 transistor was blown , so I have replaced it.

I couldnt read the label so thanks to you I know it is BU406

The fuse is ok but nothing happen when I switch it on.I reverse engineered a scheme from the board (only primary part) and downloaded datasheet

of TDA4605-2.The scheme in datasheet looks quite similiar ( mac uses optical feedback from secondary circuit in advance to flyback winding of transformator).

Anyway, the question to Honza is if the problem was in faulty TDA4605 or were there any other faulty parts? Have you any advice ? as I ordered only one piece of this IC and dont want to burn him too...

thanks,

bajin