Samsung LE37S81B only start up once

[PowerAmpFreak]

Samsung LE37S81B, strange behaviour...
Only sign of problem was secondary cap in standby supply.
Replaced, start it up, working perfectly.
UNTIL it's either shut off by user OR shut off by itself if signal isn't applied (the normal minutes)
When try to restart it - front red led flashes two rapid times and then you will get no attention from it. Doesn't matter if using remote or side keys.
Is there a known issue with corrupt eeproms on these ?
(as a result of bad cap in standby supply)
You have to cycle power, and it will start again once and the same procedure.

EDIT: I just noticed sometimes it is possible to start a few times - then returns to the "locked" state.

[tom66]

Re: Samsung LE37S81B only start up once

Yes, do a reset. I have seen this before with buggy eeprom.
European model (from standby): Info - Menu - Mute - Power. Then find reset option and select it.

[PowerAmpFreak]

Re: Samsung LE37S81B only start up once

Update: I did a reset in service menu - no help
I also disabled the watchdog - no help
I replaced the eeprom to initiate a new memory download - no help
So, I believe this is actually caused by the PSU. I can see a pattern of behaviour.
From cold, it seems possible to start it up. As soon as the unit heats up, restart will be impossible (but if it's ON it will stay ON)

It's possible to start up the set several times during the first minute from cold.
So obviously something heats up and don't want to play anymore.

When set is plugged in I can hear a whining high frequency sound coming from the main SMPS stage (not the standby supply) which sounds like an unstable voltage regulation loop.
Since the set can be kicked on from cold there is little chance this is caused by bad caps. More to the point of cold joints.
The thing is that I already touched up some joints, but I have to check for more.

[tom66]

Re: Samsung LE37S81B only start up once

Some poly capacitors can fail when they get hot.
Pictures would be appreciated.

[PowerAmpFreak]

Re: Samsung LE37S81B only start up once

Today's update: (picture will come soon)
I monitor the +24V line from the BN44-00157A powersupply during start-up.
When the set will operate OK, the +24V line will come up very fast and stable.
The time the set will fail to start, the +24V line jumps to +8.7V and stay there two seconds. Then drops.
I assume mainboard will hang just because of this.
So, it boils down maybe the F9222L controller will fail to start properly when hot.
This could be one of the reasons.

[tom66]

Re: Samsung LE37S81B only start up once

Consider startup capacitors, feedback IC, and any nearby poly-film capacitors. Pictures would help. If you get the BN44 number I may have a schematic.

[PowerAmpFreak]

Re: Samsung LE37S81B only start up once

I replaced the erroramp (TL431) and associated optocoupler.
Crossed fingers, it *appears* to startup every time from now on.
I already replaced startup caps and filtercaps to F9222L just in case.