parts list cross ref for MC2105....

[gkargreen]

or 2300 as I have been informed that they use similar driver boards. Tried to search here on AK but not coming up with anything, just bits and pieces here and there. I am trying to find a xref for m153539, thanks.

 

[c_dk]

Looks like a motorola number. What is the Mac part number or at least the schematic number?

 

[gkargreen]

Q111 = 132-038, thanks!

 

[c_dk]

The commercial replacement for the 132-038 is , which was a upgrade with new heatsinks different bias resistor and was a kit from mac parts, was a 2n5320. the pnp was a 2N5322 which is Q113

But you do have me confused. R135 is connected to the collector of Q113 not Q111.

 

[gkargreen]

Sorry fingers slipped, that is R133, not 135. BTW, going thru and checking the replacement transistors which are Sylvania ECG 238, would you recommend just going ahead and replacing them with the ON15003? Also, I am guessing that these should have mica insulators with heat sink paste, correct? Thanks!

 

[c_dk]

Yes on the Onsemis and paste, no on the micas. Only the one transistor on the negative heatsink gets a mica insulator, puts R159 and 160 in the circuit. Top two transistors on the inner heatsinks I think I remember.

 

[gkargreen]

Thanks, dk, from what I see there are mica's on the top transistors of each heat sink only, the middle and bottom transistors are mounted directly to the heatsink.

 

[c_dk]

I lost power so I am stuck with a KR9600 I can not test and a Ipod for music.

I do believe it is only the last negative output that gets a mica to lift the collector from the electrically hot heatsink.

 

[gkargreen]

dk, so far I have two bad transistors, one in each channel and all the bottom output transistor. Would you recommend replacing the whole string of three with the Onsemis, or take two of the good original transistors and use them to make up a good right channel? The left channel is all Onsemis, having replaced the ECG rail with Onsemis and the other rail with ONsemis too as that was the first channel I found a bad original transistor. Now working on the right channel and what do you know, a bad transistor on the bottom (heatsink) so was wondering if I should go with ONsemis or use my leftover original transistors. Thanks!

 

[c_dk]

I believe the Mj15003Gs are what $6.00 with shipping at Mouser, to be used in a amp that routinely will sell used for a grand........yea replace them all. Carefully check the wirewounds. They need to be Cobers or Rockwoods to be factory and they must be inductive!! If the partial repair back in the day used ECGs you were asking the amp to oscillate.

 

[gkargreen]

Thanks, dk! I have been checking the wirewounds, so far, all the ones tested are good, or rather, not open, don't have a 4 wire resistance meter to measure down that far into the weeds, but they seem to all be under 0.8 ohms or less.

 

[gkargreen]

dk, i am in the process of installing new power supply caps (the big ones) and I note that the new cans don't have the plastic bosses nor extend out like the original cans, any suggestion on how to deal with that issue? Thanks!

 

[c_dk]

You need to get the correct caps or access to a lathe to make your own insulated support sleeves.

 

[gkargreen]

Hi, dk, well, it works! Thanks so much for your guidance. I do have one problem now, and that is the speaker switch, it is cutting in and out in the right channel when I move the amp around, do you have a real part number for it, mac has part number 146-103. Thanks!

 

[c_dk]

There is no replacement that I know of......I have had to jumper the leads. It is a double pole single throw AC power rated switch but a pheolic contact holder breaks inside.