http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27678096 en Fri, 24 May 2013 01:36:25 EDT Fri, 24 May 2013 01:36:25 EDT http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27721619
one output transistor on each bank of the output stage had a C-E short.

Less obvious was a current steering transistor earlier in the circuit which was pulling the + bank toward the pos rail.

Finally, a quad op-amp near the input stage. That was it.]]> http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27721619 Tue, 13 Nov 2012 06:22:32 EDT http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27709774
I hate the "I've fixed it/solved the problem" without WHAT fixed/solved it posts. Please enlighten us. Inquiring minds want to know.

Had someone before you had a similar/same issue AND posted the fix for it/details, it might've made it easier for you (and anyone else afterwards)

Although with a brand like Marshall (amps) , they want their gear working, so direct contact works well, I know Mesa Boogie/GK/Trace Elliot does.]]> http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27709774 Thu, 08 Nov 2012 23:40:28 EDT http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27708354 http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27708354 Thu, 08 Nov 2012 15:44:25 EDT http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27705918 http://www.dslreports.com/forum/Re-Marshall-MB450H-Schematic-27705918 Thu, 08 Nov 2012 04:24:18 EDT http://www.dslreports.com/forum/Marshall-MB450H-Schematic-27678096
Amp had one shorted (C-E) device on each half of output stage. Replaced all outputs and did a low voltage mains test with about 10 vac at the line input, but noticed something appears to be loading down the positive power supply, which is producing tons of ripple and falls to .5 volts immediately after power is cut off. Resistance measurements across the supply rails are in the megohms. Circuit is convoluted and everything related to power and output are on one PCB, which is becoming a mess to troubleshoot without a schematic.

It appears that someone replaced the bridge rectifier before this hit my shop. At the moment, I've done all that I can without a schematic, chasing down the obvious areas.]]> http://www.dslreports.com/forum/Marshall-MB450H-Schematic-27678096 Wed, 31 Oct 2012 02:02:44 EDT