( Vestel ) badged Digihome PVR80 80G pvr

[N_Cook]

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.

 

[Franc Zabkar]

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.

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.

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. ?

Is there a TVS (transient voltage suppression) diode?

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.

I would think that most of the larger chips would be powered from 3.3V
or less.

- Franc Zabkar

 

[N_Cook]

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

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

 

[Franc Zabkar]

Would a SM transient suppressor have a distinctive package./ overlay
designation?

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.

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

Could it be an LDO regulator with an on/off pin?

- Franc Zabkar

 

[N_Cook]

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

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

 

[N_Cook]

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

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.

 

[Franc Zabkar]

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?

This TVS diode protects the +5V rail on some HDDs:
http://www.onsemi.com/pub_link/Collateral/1SMA5.0AT3-D.PDF

- Franc Zabkar

 

[N_Cook]

Back working again, the first digital TV thingy I've repaired.