Overview
Some notes on repairing the motherboard of the Epilog Helix.
See Graham for more details.
Symptoms
Epilog just stopped working, no control panel or any other indication of life. Main clue was visibly burned chip U31 on main control board.
Similar to this one from some other Epliog. Ours was worse.
Diagnosis
- The most evident problem is that there's a burned U32 LT3430 step-down voltage regulator which evidently produces the 5V rail from the 48V rail. The circuit looks to be very similar to the "Typical Application" in the LT datasheet.
- Googling: Others with same problem note that the accompanying Schottky diode is shorted. Ours was also.
- In addition, on removing the LT3430, I noted that there's a large square thermal pad under the chip. This is required (per datasheet) to be soldered to the bottom of the chip as a heat sink. However, on this board the solder mask covers the pad, so no heat-sink action.
Picture of our Epilog shows U31 already removed, burned traces adjacent, D19 to the right. (Note also U31's square thermal pad that is covered with solder mask so obviously not working as designed.)
References:
Repair strategy
To avoid having to
- Repair the burned section of the board
- Look for other associated components which might be damage
- Simply recreating a circuit which failed (note missing heat sink)
... it seems it might be a good idea to repair by replacing the existing LT3430 with a DC-DC converter module.
- Original LT3430 has max 3A output (assuming heatsink!).
- Tempting to get DC-DC module with higher capability,
- but any overcurrent protection would engage at a higher current.
- and it's likely that LT3430 was operating below maximum, considering lack of heatsink.
Parts used
Part
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Key specs
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Part
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$
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DC-DC converter
|
>48V in. 5V out. >=3A out
LT3430 has remote on/off pin, but not connected on Epilog.
Package:
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941-1574-ND,Delta S36SE05003NDFG,DC/DC CONVERTER 17W 5V 3A
- Encased
- Very complete specs, lots of protections
- Requires input fuse: 2A slo-blo fuse (that seems excessive! 48V x 2A ~= 100W! Output is only 15W)
|
$27.62 |
Input cap
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DC-DC data sheets say:
33u 60V <0.7 ohm ESR at 100kHz
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565-2335-1-ND,EMVH630ADA330MJA0G,CAP ALUM 33UF 20% 63V SMD |
$2.02 |
Input fuse holder
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Most DC-DC data sheets say: needs input fuse.
Some want fast acting. Delta wants slow blow.
6A output = 30W -> 30/0.85 eff = 35W. 35W@48V = 0.74A
Fuse size: 5mm x 20mm would be easy to fit.
|
F6094-ND,0PTF0078P,FUSE BLOCK CARTRIDGE PCB |
$1.35 for 3
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Fuse holder
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5 x 20mm fuse holder.
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507-1246-ND,5ST 1-R,FUSE GLASS 1A 250VAC 5X20MM |
$2.08 (for 10)
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|
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Installation
- Removed U31 and D19
- Assembled the parts on a small piece of Veroboard
- Created some brackets to mount the new assembly above the main board, in close proximity to U31, so that lead length is minimized.
- Wired the input of the regulator (via fuse) to 48V
- Wired the ground of the regulator to ground near U31, and + output of regulator to +5V point on main board.
Resul
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