was intermittently failing to power up , now no power up. mohmeter reads 0.13 ohm +/- 0.01, loading the 5V rail to ground on the main board, HD etc disconnected. Not any of the 10 electrolytics or a power 3 lead SM device. What to try next , monitoring the 0.13 ohm while flexing the board. ? Powering with a current limited bench power supply set at 5V ? oh for an IR camera for a piece of test gear. If the big BGA chip gets hot, then a chuckit job.
( Vestel ) badged Digihome PVR80 80G pvr
Jul 26, 2009
7 Replies
On Sun, 26 Jul 2009 15:59:23 +0100, "N_Cook" put finger to keyboard and composed:
It would seem to me that such accuracy would allow you to narrow down the general location of the short ... unless the PCB has large power and ground planes.
Is there a TVS (transient voltage suppression) diode?
I would think that most of the larger chips would be powered from 3.3V or less.
- Franc Zabkar
Please remove one \'i\' from my address when replying by email.
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I suppose solder a good thick lead to the groundplane, for mohmeter, is the way to go there. Would a SM transient suppressor have a distinctive package./ overlay designation? I assumed the SM 3+1 lead device was a 3.3V regulator "shorted" between 0 and 5V, logo looks like DN in a circle
On Mon, 27 Jul 2009 08:16:37 +0100, "N_Cook" put finger to keyboard and composed:
The ones I've seen on hard drive PCBs are flat rectangular 2-pin packages. I can't find a circuit reference on the PCB of my Seagate drive, though.
That said, I'd be surprised to find a TVS diode in a closed system, ie one where there is little chance of user interference.
Could it be an LDO regulator with an on/off pin?
- Franc Zabkar
Please remove one \'i\' from my address when replying by email.
Whatever it is , I isolated one pin and it is not the cause of the loading. No nearby L/s for it being bucky/converter
Cold mohmeter checking probably would have worked as about 0.04 ohm across the defective item. Only 6 diodes it would seem on this board, so i checked, and one across 0 and 5V. I'd not thought of checking diodes , as why across
5V. So a half size 4148 looking barrel SM "diode", overlay saying D, directly between the, scalpelled off , leaving now separated 5 and 0 rails. What to replace it with ? 6V, 7V or 10V suppressor , what is usual? Looking under a 30x microscope is like seeing canals on mars, can just make out what looks like a lower case "r" and a smudge. Not the slightest look of distress to this item. As this pvr was previously intermittant then hopefully nothing else would have been knocked out.On Mon, 27 Jul 2009 10:05:49 +0100, "N_Cook" put finger to keyboard and composed:
This TVS diode protects the +5V rail on some HDDs:
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- Franc Zabkar
Please remove one \'i\' from my address when replying by email.
Back working again, the first digital TV thingy I've repaired.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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