What are R177 and R176 for?

[yaqube]

Those two resistors limit maximum current for U198 which is -5V voltage regulator (and also decimates power to relieve U198). This voltage regulator is fed from -12V power supply line.

Please measure and report the voltage on all three pins of U198 (7905 part type) so we would be able to give you a clue what has been broken.

[yaqube]

There might be two causes:

* Broken U198 (short circuit inside the device between pin 2 and 1 - it happens sometimes but very rarely. To verify this you need to remove this IC from the PCB (or at least lift pin 2). If the voltage across resistors R176/R177 is zero so the U198 is broken.

* Shorted C199. The same as above: remove it and check the R177/176 voltage.

There might be also a short circuit across PCB traces. Careful visual inspection could help to reveal it.

Please keep in mind that the case of U198 in not connected to ground but to pin 2 which is powered from -12V power supply line through R176/177 resistor pair.