Sony CMT-M333NT Push Power Error [SOLVED] - Page 1
Forum section: electronics / repair

author: weirdoku
author_rank: Newbie
timestamp: March 31, 2025, 10:00:02 am
content: Hi all new here!Hoping to get some advice. I have a Japanese Sony CMT-M333NT I imported from Japan few months ago to UK here. It has been working flawlessly until the other day when a push power protection error appeared and the speakers started making a loud hissing/cracking noise.It's a Japanese model and I am running it through a transformer fromhere. I have another Jap 100v MD deck that I tried on the same transformer and that is working fine so I don't think it's the transformer.I’ve checked the speaker wires and can’t see anything wrong with those, tried turning the unit on without the speakers and the push power protection error still appears.I've opened it up, took out the MD section and looks like an IC regulator has burnt due to the black marks on the ribbon cable (this wasn't here before I last looked inside), the caps/components around all look okay. Had a look around the power board and amp board with a flashlight and I can't immediately see anything else that burnt.Looking in theservice manual. The regulator IC356 is a NJU7201L40(T3), I’ve found some on aliexpress so I can order replacements.So my questions are...What caused IC356 to die?What else should I check before replacing IC356? The transformer/powerboard?I'm comfortable taking the unit apart and have a basic multimeter and soldering/desoldering station so I can do some basic work if needed.Any advice/help appreciated!

author: weirdoku
author_rank: Newbie
timestamp: March 31, 2025, 03:14:49 pm
content: Got myself a breadboard and some clips to test the regulator hooked up to a 9V battery as I don't own a bench power supply.The input reading is 9.3v (fresh battery) and the output is 4.019v measuring with my multimeter which is within spec of the regulator output max 4.2v.The black marks line up perfectly to the regulator, but the regulator itself doesn't actually look that bad or part of it had melted/popped. So can a regulator still be bad even if the readings are correct?

author: Grandchuck
author_rank: Super Contributor
timestamp: March 31, 2025, 03:44:57 pm
content: Sounds like an overload or short downstream from the regulator.

author: weirdoku
author_rank: Newbie
timestamp: March 31, 2025, 03:57:09 pm
content: Apologies I am a complete beginner. By short do you mean something has bridged? Could you advise where else I should be checking please?

author: coromonadalix
author_rank: Super Contributor
timestamp: March 31, 2025, 04:57:56 pm
content: could have burn by simply over heating and the flex pcb was over it, negating air cooled circulation, or it operate at it's limit by designa stronger one could be used, as for downstream, you need to check once this regulator is removed, if you have an overload ...overload can mean a shorted part, something who consumes more current .. but not totally dead ... a capacitor who's dying ... can be anythingyou have to understand the circuit supplied bu this regulatorif everything seems okay you can use a small variable voltage controlled current matching the regulator specs, if the psu enter overload, you do have a problem, or if it work at its settled current limit kinda almost maxed out, you now know, the design is somewhat bad

author: weirdoku
author_rank: Newbie
timestamp: April 01, 2025, 09:05:19 am
content: Having a good google, I've found this forum posthttps://www.diyaudio.com/community/threads/stk-series-amp-modules-any-good.146750/It's like 50% of my problem but only to one channel and no push power error, maybe their STK was not fully dead? The burnt marks on the ribbon cable is still a mystery, as I tested the IC and it is outputting the correct readings.I found places where I can order the STK but not sure if their original or fakes. Maybe I'll take a leap of faith and just replace the STK, if it doesn't work I'll shelf the unit and use something else for now.I have taken the unit apart and I cannot see any bad caps or any signs of burning or any signs of damage but I'll be poking my multimeter around to make sure.

author: weirdoku
author_rank: Newbie
timestamp: April 01, 2025, 09:34:42 am
content: More photos.

author: weirdoku
author_rank: Newbie
timestamp: April 11, 2025, 09:55:10 am
content: I manage to fix it by replacing the STK and the IC.Maybe I lucked out that only the STK died, wasn't sure on the IC but I replaced it anyway.Not sure if the STK is genuine but it sounds the same to me and no issues so far.