1. Home
  2. Electronics Repair
  3. Sony TV model KV35S36 dead set

Sony TV model KV35S36 dead set

I found the two power supply transistors, the 2SC4834's, Q601 and Q602 shorted, and the HOT Q502, the 2SC5148 shorted also. The fuse resistor R607 was open as well. I pulled VDR601 and did not read any leakage through it but I am leaning toward replacing it and the four capacitors, C609 - C612 just for good measure along with the other parts. What is of some concern to me though is the discoloration of the board due to overheating around the flyback in the area of R536, D530, R537 and D531. These are the + and - 15V supplies right off the flyback. I'm concerned that there might be other issues with the load on the secondary side of the flyback which may have caused the heart attack in the first place. But I have no schematic for the set so tracing this is difficult. Is anyone aware of any other problems with this model or series aside from what appears to be the apparent usual power supply problems I found, that I should be aware of? Thanks in advance for any assistance. Lenny Stein, Barlen Electronics.

Reply to
captainvideo462002
Loading thread data ...

Lenny pull the Hor drive Transformer out and clean the legs first and also check for dry cracked solder in same circuit. Check that resistor off the black VDR..

Reply to
kip

Do you happen to know the value of that resistor Kip? Lenny

Reply to
captainvideo462002

I wound up changing the three transistors and the resistor. I checked the VDR and the series resistor and they were good. There were indeed ring cracks on the hor. drive transformer and various other places that I resoldered as well. the sets been operating for three hours now and it looks OK. The two power supply transistors are running fairly hot. That is I can just barely keep my finger on them. The heatsink for the HOT is warm too but not excessivly. I was always taught that if you can't hold your finger on a semiconductor while its operaing its probably running too hot. But I learned that when germaniums were still around so I'm not sure if that rule of thumb,(no pun intended) still applies. So how hot is too hot for these to run? Thanks again, Lenny

Reply to
captainvideo462002

Lenny Its very important that those 2 Reg,s are of the same type look closely at them and make sure they are matched. kip

Reply to
kip

More important to look at the duty cycle. Make sure that it is close to

50%. These should run hot but too hot to touch is probably too much and indicates a problem. It could be the PS running inefficiently or a load. The operating frequency should be well above 50kHz. If it is not, you could have a bad cap or the transformer could be bad. I have run into a few of these supplies that kept running hot and found that the freq was low. Also, the lower gain transistors run hotter. I always buy the P rank version in batches and match the gains. You can match the gains with a curve tracer or a transistor tester but you still could have variance in related parts.

Leonard

Reply to
Leonard Caillouet

The P version was what came out but I don't think my replacements were that version though. There were ring cracks around the hor. drive transformer and I'm fairly confident that was the cause of the problem. I've run the set for a few days now and it seems to be OK so I'm going to let it go. I guess we'll see. Thanks to everyone for the great advice. Best regards! Lenny.

Reply to
captainvideo462002

Sony specifies the M version for this one, so that should be OK if nothing else is off. Did you check the duty cycle?

Some of the Sony parts listings specify MNP for the 2SC4834, meaning any of the M, N, or P rank transistors may be used. I have received mostly M ranks for these part numbers and the variance in hfe has been similar to the generics from reputable distributors like Acme, B&D, and Tritronics.

Leonard

Reply to
Leonard Caillouet

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.