Bug #1184
Repair status
100%
Description
Analog board A14764
Digital board A39541 B15
Fixed eaten trace under caps.
Replaced all caps
Self-test issues:
| Test | A/D input | Required value |
| 401.1 | -76m | +/-1m |
| 402.1 | +25.0m | 27 - 37 m |
| 404.1 | 5.5705 | 3.81 - 4.61 |
| 404.2 | 4.1110 | 1.74 - 2.42 |
| 404.3 | 2.7505 | 279 - .281 |
| 404.4 | 1.3644 | 1.91 - 2.59 |
| 404.5 | 0.1282 | 3.93 - 4.73 |
| 405.2 | 11.8598 | |
| 405.4 | 11.8592 | |
| 405.6 | 11.8588 | |
| 405.8 | 11.8584 | |
| 406.6 | 11.8610 | |
| 407.1 | 2.2620 | 6.85 - 7.15 |
| 407.2 | 11.8592 | 0.5 - 0.9 |
| 407.3 | 8.9122 | 0.1 - 0.18 |
| 409.6 | 6.8057 | |
| 410.1 | 2.2621 | 6.82 - 7.18 |
| 411.1 | 2.2623 | 6.82 - 7.18 |
| 411.2 | 2.2629 | 6.84 - 7.16 |
Updated by tin over 6 years ago
Diagnostics revealed function issues - DCI measurement on ranges other than 2A was throwing some incorrect readings even with short on inputs, ACV was showing 480VAC on 750V range (no input signal) and overflow on lower ranges and ACI currents. Few other DG211 muxes, 14094 shift registers were replaced during debug process, but that was likely not necessary.
Issues fixed after U525 and 4.3V zener replacement. Original LTC1050 opamp had leaky 145 ohm between V+ and V- rails making floating supply circuitry unbalanced.
Second meter have bad LT1223 current mode operational amplifier, driving FET full-wave rectifier bridge to -12V, and screwing everything. Same dianosis errors and ACV,DCI and ACI function failures were observed. Removed U520 and powered meter without it, supply voltages on U525 become normal.
Updated by tin over 6 years ago
- Status changed from In Progress to Resolved
- % Done changed from 0 to 100