| Electronics > Repair |
| Agilent DSO9254A repair - Sequence error 1.2V |
| (1/1) |
| parawizard:
Just got it in today from eBay. Tore it apart. Thought I would create a thread. Will post pictures and progress. Unit turns on and turns off right away showing a sequence fault on sequencer 2 with the 4th supply which is 1.2V. LEDs are: Off Off Off Off On On Off Off Off Off Off Off Off Output of 1.2V rail measures 3ohm Output of 1.8V rail measures 1ohm 1.8v rail seems to be to this very large sets of memory ICs under a large heat spreader. Not sure if these are OK are not yet. Going to remove the acquisition board to take a look at the other side. |
| smaultre:
Try to check power rail SMD capacitors, resitance, heating.. |
| parawizard:
Visual inspection under microscope didn't find anything bad. Worried about the very low resistance of the 1.2V and 1.8V rails. This is modern GPU territory. No experience with FPGA and ASICs. I am going to scope rails as they come up and before they shutdown tomorrow. If I see nothing on 1.8V and 1.2V I will isolate them by removing current sense resistors and check which side the short is on Both rails are using LTC3850. All 3 sequencers are LTC2928. |
| parawizard:
1.2V, 1.8V, 3.3V, 5V are all LTC3850 There are 3 sequencers LTC2928 The second sequencer is U497 and 1.2V is the 4th supply You only need the main supply + the sequencer powersupply cable attached to test 1.8V, 2.25V(2.17V on silkscreen), 1.6V all come up to voltage 1.2V has no output EN4 signal on sequencer is present and has continuity to RUN1 and RUN2 of LTC3850 V4 signal on sequencer has continuity to output Mosfet gates are directly connected to LTC3850 TG1/2 BG1/2 pins No gate signal on all 4 mosfets 1.2V LTC3850 all pins to ground measure out very closely matching V1.8 LTC3850 Reworked area and no difference Everything is pointing to LTC3850 being bad. Ordering a new one. Also I am almost 100% sure the power switch that breaks on these often is JN2UOANAGX |
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