You guys are missing the info!! These units will not run with high standby B+. Scopes & EEPROM changes won't fix it. I tried everything I could think of. Just read again. Rono.
RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead, replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high), C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108 (130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146 volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output, & drive is + 146 volts, & unit won't start. What did I miss? Rono.
See posting with binary attachment in alt.binaries.schematics.electronics for excerpt from training manual and short description of basic SMPS troubleshooting in the posting.
Didn't they cover SMPS basic operation in one of the electronics degree classes?
Rono: Us guys are trying to give you repair suggestions with the info you post. You have the television in front of you with your test equipment. Standard troubleshooting based on the info you gave would suggest SMPS problems????? or jungle not providing startup HPulses to HDrive xstr, HDXfmr and base of HOT. Have you scoped for startup Hpulses..... maybe that is the missing info we are not seeing in your post.
-- Best Regards, Daniel Sofie Electronics Supply & Repair
Even if the advice you get is wrong, you should be more grateful to this group which has answered lots of your questions. As it turns out, the information you did receive WAS CORRECT.
The 177 series doesn't regulate at 130, it regulates more like 140 VDC. This particular smps type doesn't tightly regulate the B+ at standby, so 145-147 is normal. Once the TV starts and current loads the supply, it will regulate to within +/- 1 volt at 140.
So if this TV fails to attempt a start with the standby voltages nominal, you must check a couple of things (and I must repeat myself). The micro needs to have viable clock and data lines, which need to be checked with a scope. The micro needs 5 volts and reset line at proper voltage, and it needs a running clock (plus more). The micro queries the eeprom, so the SDL is active for about a second at plugin. If the data doesn't appear at all, you have a system control problem. If the data appears and doesn't stop after 1 second, the micro isn't communicating with the eeprom, and is continually trying. The eeprom could be bad (as another poster suggested), or there is an open circuit between the micro and eeprom.
If the data appears and stops after 1 second, the system control is most likely OK, and you need to check the horiz output pin of the T chip for horiz drive. If it appears, follow the signal to the horiz drive\output circuit.
If no drive appears, scope the clock and data lines to the T chip. If they are OK, the T-chip could be bad, the horiz drive Vcc is missing, or the horiz freq determining components off the T chip are bad.
We are missing info that YOU must provide. If clock and data are clean, what do you have at the collector of the horizonal DRIVER ?. Do you have a flatline at B+, a normal waveform, or that =BC sine wave you get when the secondary is open ?
You should be watching the scope as you try to turn it on, to determine if it's going into immediate shutdown. This can happen silently, and very fast.
This business is not succeeded in by remembering what it was last time. You succeed in this business by figuring it out. Then of course you remember it, but I simply can't be your eyes and ears, and hand to guide the DVM or scope probe.
If you're not into scopes, the SDA and SCL lines on the EPROM should be a few tenths under Vcc, and equal. If the discepancy is more then 0.3V and unequal you most likely have a bad EPROM. If changed and the symptom persists, one of the chips on the bus has a bad I2C interface.
You might just have a bad fly, the HOT waveform will tell you that.
You might also give second thought before the next time that you say that "WE" have missed something. Last I checked now, four respodents to your post are quite skilled (I guess that includes me in this case). I don't really know Kip, but in this case he made a valid point, as far as David, Dan and John go, they are definitely the kind of techs that each successful shop needs at least one of to thrive. (or even survive)
FWIW, you need a scope and to know how to use it, then you wouldn't have even asked the question. One positive thing, you only need about a
Rono, 146V in standby is normal. These chassis usually run between
130 to 140V B+ depending on models using this chassis.
Unsolder the transformer and measure all the resistors to be sure, replace 10uF 63V in two locations; both are on both sides of that STK-730, one for SMPS, one for horizontal area. I find them bad nearly
80% of time.
BUT, that can be caused by bad solder in tuner & micro grounds and that means eeprom can be corrupt. Chipper check will fix this up by reiniting the eeprom or replace the eeprom but that will be more involved setting up other settings. UGH, that why I use chipper check. and maybe have to align the tuner (57 of them for 19 channels settings in groups of 3). Service manual is a must for consulting when setting up eeprom contents.
By the way, get the horizontal driver transformer out and scrape pins on it clean get waxy stuff out of holes, reinstall & resolder. Carefully check that 2.4K off the emitter of the small SMD transistor in the horizontal driver circuit.
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.