Bug #856
Fix error 412.1 – AC amps switch
0%
Description
Failure: Cannot measure 1.7V ±0.3V at A/D IN.
The 9.2mA ohms source is turned on to dump current through switch U323 (ACAL
pulled low) to the amps protection diodes (CR305 and CR309). The three diode voltage
drop is routed through U317 (/200uA pulled low), U320 (/ACA pulled low), U510
(REL3 pulled low), U526 and Q516 to the input buffer (Q512 and U520). The buffered
signal is tied to AMP IN.
The signal at AMP IN is then routed to the variable gain ampliÞer (VGA) and, being
positive, follows the non-inverting x1 path that consists of R530, Q509, Q507, U519,
R531, U509, Q501, and U516 to pin 12 of multiplexer U511.
The output (OUT) of the multiplexer is routed through buffer U342 to ACV/A. The signal
at ACV/A is routed through U320 (/AC pulled low) and applied to the A/D buffer
(U322), which is conÞgured for x1 gain. Measure 1.7V at A/D IN.
Updated by tin over 9 years ago
9.2 mA ohm source working (309 tests PASS).
Signal path from VGA thru R530,Q509,Q507,U519,R531,U509,Q501,U516,U511 works fine too.
U342 works ok.
U302 replaced
U317 replaced
Q543 replaced, no help0
Updated by tin over 9 years ago
U521 replaced - no help
Voltage checks, V to GND| Point | #7 failed | #6 passing |
| VR502 K | 8.19 | 9.97 |
| VR502 A | 0.042 | 1.912 |
| VR504 K | -3.978 | -1.792 |
| CR534 A | 0.031 | 1.748 |
| CR534 K | 0.031 | 1.907 |
| VR513 K | 0.030 | 1.544 |
| VR513 A | -0.015 | 0.012 |
| R282.2 | 3.485 | 5.537 |
| R282.1 | -14.96 | -14.91 |
Updated by tin over 9 years ago
| Point | #7 failed | #6 passing |
| U524.6 Out | 3.999 | 3.804 |
| U520.6 Out | 0.079 | 1.909 |
| U525.6 Out | 0.128 | 4.098 |
| U519.6 Out | -0.109 | -1.914 |
| Q508 G | -15 | -15 |
| Q509 G | 0 | 0 |
| Q507 G | 0 | 0 |
| Q508 D | 0.04 | 1.558 |
| Q509 D | 0 | 0 |
| Q507 D | 14.82 | 14.82 |
| Q508 S | 0 | 0 |
| Q509 S | 0 | 0 |
| Q507 S | 1.657 | 1.574 |