This unit appears dead, main fuse T4A has not ruptured but unit will not
power up, Any advice on what to check on the saps gratefully appreciated
,thanks

On Tuesday, February 2, 2021 at 9:31:12 AM UTC-6, David Barnicoat wrote:
This unit appears dead, main fuse T4A has not ruptured but unit will not
power up, Any advice on what to check on the saps gratefully appreciated
,thanks
Does it use a wall-wart transformer/power supply?

I'd start with that.

wrote:
On Tuesday, February 2, 2021 at 9:31:12 AM UTC-6, David Barnicoat wrote:
This unit appears dead, main fuse T4A has not ruptured but unit will not
power up, Any advice on what to check on the saps gratefully appreciated
,thanks
Does it use a wall-wart transformer/power supply?

I'd start with that.


No it does not use a wall wart, internal power supply with soldered in fuse
which is not open circuit.

In article 351969505.634057982.756000.dave.barnicoat-
,
says...

wrote:
On Tuesday, February 2, 2021 at 9:31:12 AM UTC-6, David Barnicoat wrote:
This unit appears dead, main fuse T4A has not ruptured but unit will not
power up, Any advice on what to check on the saps gratefully appreciated
,thanks
Does it use a wall-wart transformer/power supply?

No it does not use a wall wart, internal power supply with soldered in fuse
which is not open circuit.

Have you got the service manual? If not, it's downloadable he
https://elektrotanya.com/samsung_hw-.../download.html

The troubleshooting flowcharts in the manual assume you're going to be
swapping out entire boards, but at least there are schematics to help
track things down to component level.

If you've confirmed that the fault is on the SMPS board, I'd check the
electrolytic capacitors (be sure to discharge them before touching
anything on the board) and high-wattage resistors (RS801, RA808) first,
as these are possible failure points that could be tested without
working on a live circuit.

The safety guide in https://www.repairfaq.org/sam/smpsfaq.htm is
extremely useful, particularly if you do end up having to investigate
the SMPS while it's powered up.

R

Rayner Lucas wrote:
In article 351969505.634057982.756000.dave.barnicoat-
,
says...

wrote:
On Tuesday, February 2, 2021 at 9:31:12 AM UTC-6, David Barnicoat wrote:
This unit appears dead, main fuse T4A has not ruptured but unit will not
power up, Any advice on what to check on the saps gratefully appreciated
,thanks
Does it use a wall-wart transformer/power supply?

No it does not use a wall wart, internal power supply with soldered in fuse
which is not open circuit.

Have you got the service manual? If not, it's downloadable he
https://elektrotanya.com/samsung_hw-.../download.html

The troubleshooting flowcharts in the manual assume you're going to be
swapping out entire boards, but at least there are schematics to help
track things down to component level.

If you've confirmed that the fault is on the SMPS board, I'd check the
electrolytic capacitors (be sure to discharge them before touching
anything on the board) and high-wattage resistors (RS801, RA808) first,
as these are possible failure points that could be tested without
working on a live circuit.

The safety guide in https://www.repairfaq.org/sam/smpsfaq.htm is
extremely useful, particularly if you do end up having to investigate
the SMPS while it's powered up.

R


Thanks very much for the info re service manual/schematic and the repair
faqs. I will check them out, I know I have 380 volts dc at the bridge
rectifier output.
D