Marantz 250M amplifier repair - part 1

This amplifier came in with its preamp, the model 3600, both in an 'undressed' state with the covers off.
The owner had tried to find the problem after some serious smoke escaped from both pieces of equipment.
The preamp was a relatively simple fix, with a couple of transistors burnt out. Finding out which ones was the challenge, as usual.
This power amp, however, is another story.
Apparently, one channel was blown. On closer inspection, it seems that both channels are faulty.
Looking at the boards, some serious rebuilding and hacking has taken place here, with most of the transistors - in fact all types of components - swapped out for newer ones. Tracks were cut and re-patched, and some serious track burning was evident.
This meant that I couldn't trust anything about it, so a full check - component by component, and connection by connection - was the way to go.
In this video, I tackle the one channel, and take it though to testing.
Some interesting faults were discovered, so I hope this log proves informative to someone out there.
Enjoy.

You can now support the channel:
https://www.patreon.com/mcaldeira https://paypal.me/macaldeira

Full info on this model:
https://www.hifiengine.com/manual_library/marantz/250m.shtml
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DIY TEST GEAR: The title says it all:
https://www.youtube.com/watch?v=7buNHf6HoDw&list=PLy5M_tA9ux7KkjmWX0I0zNocg6NF33EfL

RESTORATION BUILDING BLOCKS: A series of videos showing detailed steps used the restoration process of tube equipment:
https://www.youtube.com/watch?v=7xvTGd4ysRE&list=PLy5M_tA9ux7JSYx8z2mw303vx287LHpzf

HowTo's: Various videos on some simple techniques and projects:
https://www.youtube.com/watch?v=lgr-J_D6pSU&list=PLy5M_tA9ux7K3B77iUGyLPai3RIvJOrkO

See also playlists on some other completed restoration projects.

PHILIPS BX750A:
https://www.youtube.com/watch?v=i8U9Lteja5o&list=PLy5M_tA9ux7IG6XgctidGO0u0DeT3_CxF

TELEFUNKEN OPUS 2114:
https://www.youtube.com/watch?v=_HO2bjY5vuw&list=PLy5M_tA9ux7LhcZ9h9plfTFmjaM1mcifu

SABA UW-175-Z 3D:
https://www.youtube.com/watch?v=cca4i60ZLw4&list=PLy5M_tA9ux7IWL18nsrSf4RnjsuPjHC-p

GRUNDIG 1070:
https://www.youtube.com/watch?v=i4J5l0fwhko&list=PLy5M_tA9ux7JgnyYPRWOK763aJ8bg3iCI

SCHAUB-LORENZ GOLDY 58 type 3020:
https://www.youtube.com/watch?v=RSbt7qVed78&list=PLy5M_tA9ux7IBse5G--Kl89SPS9sATXfZ

BUSH VHF64:
https://www.youtube.com/watch?v=U--6JymkQ1M&list=PLy5M_tA9ux7KsvN5M48cX6cxN4jSz0s3X

GRUNDIG 3060A:
https://www.youtube.com/watch?v=7x2sK2GSYeE&list=PLy5M_tA9ux7L8e9h8lrHGREPqcgWO-YQm

TELEFUNKEN OPERETTE 8:
https://www.youtube.com/watch?v=5IsACM0mPzs&list=PLy5M_tA9ux7K3SXDv8Hu4uAyl1O7NE5dc

GRAETZ SUPER 171W:
https://www.youtube.com/watch?v=MhG-CH0gqm4&list=PLy5M_tA9ux7IjUykGE8neJSI6GUxMl2YG

LOEWE-OPTA MAGNET 3737W:
https://www.youtube.com/watch?v=ZSZBJ5sKQm8&list=PLy5M_tA9ux7J_hzDhnF8rs2c7wmgGfRlK

BRAUN ATELIER 3:
https://www.youtube.com/playlist?list=PLy5M_tA9ux7L3k5nPRvrk1aH764QRCTqE

LOEWE-OPTA TRUXA STEREO 4741W:
https://www.youtube.com/playlist?list=PLy5M_tA9ux7KhVk0KqPx0Wkh2KO_5f2fQ

GRAETZ COMEDIA 616:
https://www.youtube.com/watch?v=fwmW9k3TwNE&list=PLy5M_tA9ux7L5sAApLzV6xoYzmRNJpMW5

SABA FREIBURG W2:
https://www.youtube.com/playlist?list=PLy5M_tA9ux7IqvS-LshUGpE1D_WY6mrZe

GRAETZ MUSICA 4R417:
https://www.youtube.com/playlist?list=PLy5M_tA9ux7Ios98E59dWjwc2SRJyxwIn
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CAPACITOR LEAKAGE TESTER:
https://www.youtube.com/watch?v=0pySErvzUIY&list=PLy5M_tA9ux7KWexvEjLB0SANSxQXi0zTS

Видео Marantz 250M amplifier repair - part 1 канала Electronics Old and New by M Caldeira