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Hitachi 50EX20B SMPS shutdowns on brights.

Q903 (SCR) fires 1/2 of a second after bright pic appears forcing SMPS to trip shutdown mode. Leave it running with low brightness scenes no problems. Red LED (SMPS protection) dimly lit and changes in intensity while normally running (Red LED should be unlit). So know this two problems is related but what is the question.

This info I need part of schematics for power supply and horizontal section. So I can track down which is triggering SCR forcing SMPS to shut down on brights. Chassis is functioning normally, voltages are stable, fixed at 115V B+ via the SE115 IC.

BTW, this is AP52 chassis. I have other schematic for 50FX20B and it is not quite similar.

HISTORY: had to replace STRM-6511 IC to get SMPS running. Chassis already had caps replaced in many key areas.

Cheers, Wizard

Reply to
Jason D.
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Jason: I have 3 .pdf files from Hitachi + 2 .jpg files (Total of about

2MB) that I could send you as Email attachments if you want to send me your Email address. My address is snipped-for-privacy@bellsouth.net

Robert McPherson

Reply to
rm502

You can still download the service manual from Hitachi with your account access.

As I recall, look for a leaky zener diode in one of the protect circuits. Since all shutdown sense circuits pretty much tie into the shutdown scr, you need to narrow down which one is tripping the set.

In addition the current sense low value resistor for the main b+ has been found to be bad after smps ic failure.

Reply to
dkuhajda

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