You have GOT to be kidding me. All that work to replace a +15v LDO and my stereo takes a dump again a few months later.
- +15v shows ~0.75v when powered up.
- Remove the +15v LDO, check operation of just the component as a sanity check, shows +15v. Must be a problem on the power PCB.
- Study the +15v network, remove most BUT NOT ALL cables carrying +15v to other PCBs.
- Painstakingly remove nearly all components on the +15v net, problem still exists.
- Realize later that +15v is still being carried via cable to other PCBs. Remove cable going to Volume PCB, problem goes away.
- Remove all Volume PCB cables and restore power PCB cable connecting the two boards, problem persists. Problem exists on Volume PCB.
- Look over volume PCB, no obvious shorts or component damage.
- Recall that spinning the input selector knob after CHECK POW5 fault would make system exit standby. TC9482 digital volume control ICs both take simple serial comms from the DSP board. Coincidence?
- Larry’s Corner website shows a bad TC9482 IC. Order 3pcs Toshiba TC9482 in the wrong IC package from eBay, order SOP28 – DIP28 convertors from Amazon.
- Do a little test; cut GND traces feeding each TC9482 (IC11, IC12). Apply power to the volume PCB, voltage holds steady (at ~10.6v in CC mode set to 100mA). Take tweezers and bridge this connection on IC11, voltage droops to ~8.5v, doesn’t look like a short. Bridge the GND connection to IC12, DEAD SHORT.
- Replace IC12, restore cut traces to IC11 and IC12. SHORT AGAIN. Re-cut trace to IC12 and increase CC to 300mA, voltage steady. Did I just replace the wrong IC?
- Replace IC11, restore traces, apply power. Not a dead short, but gets there within about 10 seconds. Both IC11 and IC12 feel hot! Eff this, cut supply traces to ALL the opamps IC13 – IC17.
- Wire up IC17/IC14, steady ~100mA draw. Wire up IC13/IC16/IC15, climbing ~100mA draw.
- Replace ALL opamps. Restore supply traces and put everything back together in one last-ditch effort. Power up, immediate shutdown, “CHECK POW5”.
- List on eBay for parts: http://ebay.us/mUJme7?cmpnId=5338273189
- Bye Felicia.