FIXED - Sanyo TV + 17PW20.1

[dumpystig]

First post here so hello to all you experts who I am hoping can shed some light on the following dilemma.

The TV is a Sanyo CES37WSD7-B, 17PW20.1 PSU, 17MB22-2 A/V I/O. The fault is similar to (but not the same as) many I have read about the past few days, regarding the standby freeze/LED staying on. Here is the sequence of what happens:

- Plug TV in; LED off
- Enter Standby by pressing button on TV; LED illuminates brightly for a split second then immediately dims to around half that initial brightness. TV buttons and remote have no influence - only the Standby button will work.  
- Leave TV in above state; after anywhere between 5-40 minutes the backlight will come on, the screen comes to life and then functions as normal. Slight buzzing from bottom right area of PSU, faint but audible when I get near.

All the caps have been visually inspected (I don't have the appropriate test equipment, just a DMM) and none show any bulging domes/splitting sides or any leakage. What I have spotted is that the main smoothing cap (C819) has been replaced - it should be 220uF but the replacement is 150uF. I have done a shed load of resoldering to try and eliminate any dry joints. Once the set is up and running all voltages are as indicated on the schematics.

My thoughts are that the smoothing cap being a lower value is probably the culprit, but confirmation of this or any other indicators of the fault would be welcome.

Thanks,
Mark

 

[watteau]

Hi Mark,
Have you checked the stand-by voltage on D823, when the
fault is present (it should be about 11.5V).
If it's low, the most common problem are the two 4700u 6.3v
caps. C818, and C857, in the stand-by secondary circuit.
Regards,
John.

[dumpystig]

Hi John, thanks for reply.

Voltage at D823 = 10.5V, would you regard this as being low?

[dumpystig]

And PL805, pin 12 (+5VSTBY) = 5.08V

[watteau]

Yes that voltage should be Okay, there should also be a 3.3V on 11/12 of PL805, and the 5V
on pin 13, when in stand-by.
The  power-supply 'run' voltage goes in at pin 6, of PL803, and should be 1.7V when in
stand-by, and 0V when running.

[dumpystig]

OK, after trying the 'Menu-4-7-2-5' trick all that's happened is the LED is now at full illumination constantly with standby button pressed in; neither remote or side buttons have any effect.

Voltages at present state:

PL805
- Pin 11 - 3.3V
- Pin 12 - 3.3V
- Pin 13 - 5V

PL806
- Pin 6 - 54.7mV

So the 'run V' is not present... maybe this indicates a fault on the 17MB22-2? It seems as though something needs to warm up before standby will kick-in...

I've read about checking the small side button board, it's 3.3V at the Zener and 8.6V at the input from PL811 on the PSU.

[watteau]

Hi,

Yes, it sounds like a main PCB problem, have you tried warming
the main PCB with a hairdryer to see if that will localise the problem?

Here's a link to some info. I found about this chassis:
http://www.megaupload.com/?d=ER9AMF73

Regards,
John

[dumpystig]

Hey John, that's a great find, I've searched everywhere for a service manual but there's very little Sanyo literature out there. Although it's for a different model after a quick glance I'm sure it will be a great help to me. I made a chart of all voltages last night so I can do some cross referencing and should be able to pinpoint the fault, or at least narrow it down somewhat. Hopefully when I return I can post the fix for future reference.

Thanks again pal,
Mark
 

[dumpystig]

FIXED - 17MB22-2 Chassis, 17PW20.1 PSU.

I've done tons of searching on this topic and both these boards, and I mean tons. The link that John watteau gave me helped with some extra reference voltages. There was incorrect voltage @ PL803, pin6 - should be 1V7 standby but was only 58mV. I got a few pointers from this site (although for a different board), and also from a Russian site, even though the translation wasn't brilliant!
It turned out there were quite a few dry joints so, besides all the major heavy joints I did at first, the following are where I had success, all on the PSU:

- Q804, Q805 - part of ST_BY/ON/OFF circuit
- R913, R914, R915

I'm still only getting 334V @ run across C819, not 390V as indicated on circuit diagram, but all other V's are fine.

Many thanks to you John, that d/l link you gave me helped a lot.