• Please note that Audiokarma will be offline briefly for updates early on Monday morning, September 28th.

MC2125 with bad Drivers

The thermistor is the component in the circuit between the supply rail (+/-42) and the base of the drive transistor (TO-3), one on each half of the output heatsink. Nominal resistance is 500 Ohms.
 
Thermistor R279 caught on fire. The other three R295, R280, R296 on the heatsink are ok. There are other thermistors in the circuit. I though you were asking about the other ones.
 
Last edited:
clinic-audio said:
Hello

Is this thermistance (used in MC2125 and MC2205) you are talking about ?
Click to expand...

If you hold your fingers across them, how fast does the resistance drop? Also, they appear to be wrapped in heat shrink. Is there a glass device under that cover? Amphenol may have a device with possibly the necessary characteristics.
 
Last edited:
Hello Patrice!!! I did not hear back from you. So, I did not send to you the last service manual for the MC2205. I registered on some of the French and European Hi-Fi forums for the fun of it. Going back 20 years or so, I find that there is a lot of interesting talk on the web. I looked for some of the music people enjoyed and stream it if available on Amazon.
 
Hey! You caught me off guard and eating lunch. That is the device I was looking at. It was nice that the individual at McIntosh mentioned a beta value of 1600. That is a lot of change in resistance to a little change in temperature. Are you game to remove to good one to do a few resistance tests say at night when it cools off and then during the daytime out from the Sum with a DVM to get a reference? The 25/85C curve of the Amphenol device could then be compared.
 
Kingbleu said:
Long time no see. I found a bad diode on board 128-355. Can you help identify. I can't find the newer manual for the 2205 that you mentioned in the earlier post.
Click to expand...
Oh! Hello friend. While it is warm outside, I am enjoying getting out and being with friends and family. A little dirt or grease under the nails is more satisfying feeling rather than some of the draining experiences here on the forum that can leave you exhausted, frustrated and misunderstood.

I needed a break from the ultracrepidarian, pedantic or sophomoric individuals on the forum and choose to be in the background.

You can always message me. I do not believe the word searches by moderators are as bad as eBay.
 
Diode FDH400 is installed and the amp is currently on the bench. Both channels track evenly. The amp tested at 136 watts. It is currently idling at 30 watts on start up. This was measured with a speaker load and no signal. The right meter is not working and is next on the list.

I think what caused the fire was that the driver board made contact with the autoformer underneath it. I put some plastic washers on the standoffs to lift up the driver board higher.
 
Kingbleu said:
Diode FDH400 is installed and the amp is currently on the bench. Both channels track evenly. The amp tested at 136 watts before clipping. Bias is currently idling at 30 watts on start up. This was measured with a speaker load and no signal. The right meter is not working and is next on the list.

I think what caused the fire was that the driver board made contact with the autoformer underneath it. I put some plastic washers on the standoffs to lift up the driver board higher.
Click to expand...
 
Hello Kingbleu

The driver board can't touch the autoformer , there is something that you schould know , the autoformer which is under the pcb is not the same channel , for the left driver board this is the right channel who is above
 
Left meter is not workig. I swapped the Lm301 chips with the working meter. Pulled and tested all diodes and checked resistors for the left meter. Trim pot is good. Im running out of ideas. Maybe the meter itself got damaged itself.
 
You must log in or register to reply here.
Back
Top Bottom