Hi, Have a Toshiba 21inch colour TV with no vertical deflection. One single bright line across in the middle of the screen. Checked for bad caps and vertical IC LA7837. Found that pump-up supply voltage at Vcc pin8 is only 2 volts. It's suppose to be 24v as per Sanyo IC specification.

I traced pin 8 and found it was connected to another IC M52707SP-A at pin 26. I disconnected all components to this pin and measure the voltage and I got only 2v.Im unable to find any details for this M52707SP-A chip.

I understand most Vertical IC recieve its Vcc supply from scanPS. But this one comes from another chip M52707SP-A(Mitsubishi). I do not have the schemetics and at a lost of what to do.

Hope someone can point me in the right direction or let me know any other test I can do to pin down the problem. It has taken me 2 weeks to this stage now. Thanks in advance.

roger

Roger,

I didn't find any data on M52707SP-A either. Vance Baldwin Electronics at 1-800-432-8542 had Toshiba 2050RE listed on their site. You might try calling them to see if they have a datasheet or stock that (obsolete) part.

What voltage did you measure at Pin #1 of IC LA7837?

Lenny

Thanks Lenny for the reply. The Vcc of pin 1 I got is 9V. According to Sanyo data it should be 8-14V. So the problem is the Vcc pin 8, which should be 24V, but I got about 2V instead. Oh yes, the LA7837 feels cool even TV is on for an hour.

Normally the 24v comes from the FBT and not from that ic.

Yes, I agree with you completely. I saw shematics of other brands and most drive from PSscan power from FBT. That's way Im stuck here. I traced that pin back and it came from another chip......im puzzled.

Maybe this trace feeds this other chip along with the vert IC?

If you follow the trace very carefully, there are no other resistors, diodes, or wire-bridges on that trace that may have the voltage originate somewhere else?

Let us know what you find.

Lenny

Hi Lenny and all. Im very sorry. It is my mistake. The Vcc does branchs out to the pin 6 of FBT. Guess I did not look hard enought.

FBT pin 6 is supplying 45v ac and passes thru a diod which retify it to 32v dc. Now, I found that there is a component which looks like a film resistor. It is labelled ZP03 on the PCB and has a number 500 on itself. It is yellowish colour and does not has an bands on it. The volyage drops to 2V after this unknow component. Can someone tell me what component is this?

Oops...the above posted by me.

BTW, I did check RS component website but cannot find anything similar.

A couple of suggestions.

1. Look for another component with the same (or close) markings on it and measure that one to see what it measures.
2. Measure the suspected bad component in-circuit first, then pull it off the board and measure it again.


See the following link for some info about chip resistors:

http://www.talkingelectronics.com/ChipDataEbook-1d/ChipDataEBook-1d.html

That seems to indicate it might be a 50 ohm resistor.

Hi Lenny and all. I managed to solve the problem. The faulty part is a Pico Fuse....the yellowish component I mentioned earlier. It is a 500mA fuse that is burnt and hence no supply to VCC8. Thanks once again.

Hey Roger!

You did it!

GREAT FIND! GOOD FIX!



Lenny