Fixing Roland BR900-CD digital studio recorder

[domu]

I am struggling to fix older piece of audio equipment BR900-CD. I have disassembled it to replace a pot, and after reassembly it wont boot. After powering on you can see LCD animation, some LED light up and fade slowly (like power went off), and everything hangs - nothing works. Also LCD backlight works no more.

I have compared voltages on some ribbon connectors and before when it was still working voltages were slightly higher than now. For example: 3.60 -> 3.12, 4.56 -> 4.21, 8.24 -> 7.88.

Original input is 9V DC. It is converted down the road by voltage regulators to 5V and 3.3V.

Any clues what can cause that voltage drop ? Is it rather cause or the effect ? How could I go about to troubleshoot it ?

Unfortunatelly schematic is impossible to find.

[Mick Bailey]

Maybe the 3.12v is below the threshold voltage for the main CPU, but I'm just guessing. You could try contacting Roland for a schematic, or preferably the service manual. At the time it was manufactured there must have been some supporting documentation for their service centres.

Have you re-traced the steps you took when replacing the pot to make sure a connector isn't reversed or 1 pin out, or even if you have a solder bridge somewhere? All it needs is a tiny bead to bridge tracks and you've got a fault.

Before you replaced the pot did everything (apart from the pot) work correctly?

[olddawg]

Usually.. old digital stuff from that era are plagued with failing surface mount electrolytic caps. Got an ESR meter?