defconklaxon
New Member
Hi all,
I have an MC2200 that recently had the right channel fail. I'm in the process of rebuilding the power section and have a few questions. Here's the rundown:
1. It is obvious this amp has been serviced before, as the transistors have date codes from 1976, 1979, 1992, and 1993. So obviously this amp is not stock from the factory and I've noticed some sloppy work that now makes sense.
2. Every power transistor has an insulator but it's not mica, it has a metallic appearance. I've done a lot of searching around the forum and it looks like some other amps (2100 series, 2300 series) only have insulators below the driver transistor, as its collector isn't connected to the voltage rails and the heatlinks are "live", but isolated.
3. Taking my DMM to the metallic looking insulators, I do not measure any continuity when putting the probes on a single side of the insulator, or on each side. However, which potentially worries me, is if I take hook probes and connect to the holes sideways (the probes are parallel with the surface of each side, in other words) I do measure continuity on all four that I've pulled from the heatsink thus far. So is there a metallic layer sandwiched between the outer layers? Is it normal to measure continuity if you hook into the holes like I have described?
4. Related to 1, I have no idea who has serviced this amp and thus don't know if every transistor should have an insulator or not, maybe they were added unnecessarily? The amp worked well for approximately six years before the channel blew so my guess is the insulators aren't the cause of the issue nor are they critical, but wanted to ask people with more experience fixing Mac gear than me.
5. Finally, are the Mac insulators something special? Could they be replaced with mica or would that be a bad idea? I've done a ton of searches for info regarding these Mac insulators and have found pretty much nothing, nor do I see them mentioned in the service manual. Thus, any insight from you guys is greatly appreciated.
Thanks!
--Phil
I have an MC2200 that recently had the right channel fail. I'm in the process of rebuilding the power section and have a few questions. Here's the rundown:
1. It is obvious this amp has been serviced before, as the transistors have date codes from 1976, 1979, 1992, and 1993. So obviously this amp is not stock from the factory and I've noticed some sloppy work that now makes sense.
2. Every power transistor has an insulator but it's not mica, it has a metallic appearance. I've done a lot of searching around the forum and it looks like some other amps (2100 series, 2300 series) only have insulators below the driver transistor, as its collector isn't connected to the voltage rails and the heatlinks are "live", but isolated.
3. Taking my DMM to the metallic looking insulators, I do not measure any continuity when putting the probes on a single side of the insulator, or on each side. However, which potentially worries me, is if I take hook probes and connect to the holes sideways (the probes are parallel with the surface of each side, in other words) I do measure continuity on all four that I've pulled from the heatsink thus far. So is there a metallic layer sandwiched between the outer layers? Is it normal to measure continuity if you hook into the holes like I have described?
4. Related to 1, I have no idea who has serviced this amp and thus don't know if every transistor should have an insulator or not, maybe they were added unnecessarily? The amp worked well for approximately six years before the channel blew so my guess is the insulators aren't the cause of the issue nor are they critical, but wanted to ask people with more experience fixing Mac gear than me.
5. Finally, are the Mac insulators something special? Could they be replaced with mica or would that be a bad idea? I've done a ton of searches for info regarding these Mac insulators and have found pretty much nothing, nor do I see them mentioned in the service manual. Thus, any insight from you guys is greatly appreciated.
Thanks!
--Phil
