Sharp MD Players (MT66/MT77) That Won't Power On: Repair Notes (Mostly Blind Luck)
Someone recently messaged me that their Sharp MD player won’t power on. I’ve previously written two posts about dead Sharp MD units, so here’s a reorganized write-up to give anyone hitting the same problem a few ideas.
Sharp MD players have two notorious common faults: shattered gears and dead-no-power. They tend to split by model — the MT66 and MT77/877 rarely suffer shattered gears, but these two “sleep to death”: even a brand-new unit, left sitting unused for a long time, will refuse to power on when picked up again, which tanks its value. I’ve previously revived several units like this, including MT66/MT77 models — but if you ask me for the exact root cause, I honestly don’t know. Really! Every single one of them just… came back to life on its own while I was probing it on the bench.
The first unit I ever revived: I was probing around IC401, casually poking a few voltages with the multimeter, and it just powered on — as if some capacitor was the culprit. One unit proves nothing, so I found another one with the same symptom. My guess was a stuck power IC state or an aged capacitor, and my earlier probing had effectively injected some impedance that pulled a level back into range or changed a load capacitance. So I pulled out the Service Manual, ready to check the RESET/VCC signals and capture the power-up sequence on the scope. Given how badly I slept through digital/analog electronics and signals & systems back in college — and how little attention I paid the oscilloscope in lab class — it’s no surprise the scope was probably misconfigured: nothing I measured looked right, nothing matched expectations. Then after another round of random poking, the unit came back to life. A later MT66 with the same symptom went down the exact same path.
Things worth trying
- Set the bench supply to 1.3V. Don’t ask me why — the first unit mysteriously recovered while powered at exactly that voltage.
- Find a ~100kΩ resistor and try discharging the RESET / VCC / XTAL / PLVBAT pins of IC401 to ground.
For those who know their stuff: help pin down the real cause
Grab the MT77 Service Manual, power it up (or rather, fail to), and record the static voltages on these pins with a multimeter, then follow up with a scope:
- RESET (pin 59) — is it stuck low?
- VCC (pin 62) — is there a ramp-up at all?
- XTAL (pin 63) — is the crystal oscillating?
- PLVBAT (pin 52) — compare against a working unit
