- Schottky diode in SM PSU o/p? - 2 Updates
- Vivitar 3500 "zoom thyristor" flash won't whine - 2 Updates
- Zenith SF3537H modules wanted - 2 Updates
| T i m <news@spaced.me.uk>: Oct 11 08:02PM +0100 On Sat, 10 Oct 2020 09:34:11 -0700 (PDT), John-Del <ohger1s@gmail.com> wrote: <snip> >> This is the PSU OOI: https://ibb.co/VtBY4Rt >> The IC is a CR6338T. <snip> >Years ago when everything was discrete, we saw plenty of power supplies so badly designed that an excessive load or even a brown out would cause a catastrophic failure (Sony). ;-( >Today, an properly designed IC SMPS controller is literally pennies each, and they have all that solved internally. Ok. >Your IC does have a soft start internal to it and overcurrent protection, so the shorted Schottky diode did not seem to destroy the IC Phew. >(check pin 5/6 to 4, should be no short on the internal mosfet). 5/6 to 4 test out like a pair of diodes but with a low resistance (either way) between 5 and 6? Cheers, T i m |
| John-Del <ohger1s@gmail.com>: Oct 12 07:38AM -0700 On Sunday, October 11, 2020 at 3:01:40 PM UTC-4, T i m wrote: > 5/6 to 4 test out like a pair of diodes but with a low resistance > (either way) between 5 and 6? > Cheers, T i m 5 and 6 should read short as they are the common drain pin and internally tied together inside the IC. Don't use the diode scale when checking for leakage between those pins. Pins 5 and 6 are the drain, and pin 4 is the source. Out of circuit, it should read virtually open between pins 5/6 to pin 4. |
| Cydrome Leader <presence@MUNGEpanix.com>: Oct 12 04:28AM > Someone on the EEVblog forum says the part number is actually 2SB324, which > is a germanium PNP transistor. I'd guess I won't find a direct replacement > for that. NTE still sells crosses for stuff like that. Looks like NTE102A. Must be old stock. I doubt the chinese would even fake those. |
| abrsvc <dansabrservices@yahoo.com>: Oct 12 05:57AM -0700 On Monday, 12 October 2020 00:28:53 UTC-4, Cydrome Leader wrote: > > for that. > NTE still sells crosses for stuff like that. Looks like NTE102A. Must be > old stock. I doubt the chinese would even fake those. OP may provide details, but I supplied transistors to him and as of this writing, one is working by changing transistor and some caps. Dan |
| Cydrome Leader <presence@MUNGEpanix.com>: Oct 12 04:22AM >> for your credit? > Heh, I think they want to fix it because it weighs around 270 pounds and > it's a struggle to move around. This seller accidentally listed one as shipped with USPS first class package https://www.ebay.com/itm/zenith-tv-35-1990-SF3537H-/203031486909 It like how it's posed on that jack thing for moving heavy, annoyingstuff. Heck, that cabinet is big enough just to fit a last run Panasonic CRT television inside of. Not even kidding either. Might be a fun project. > was missing. Just a couple connectors laying where the module went. Oddly > enough the sub-woofers were there, just missing the amp for them. > How they q/c'ed that for resale is beyond me. Just have been an "honest" mistake. Any idea where they rebuilt all those modules you had to swap? I kind of liked their 70s console TVs with the weird plastic pedastal and the preposterous "zoom" button. |
| bje@ripco.com: Oct 12 12:51PM > Just have been an "honest" mistake. Any idea where they rebuilt all those > modules you had to swap? I kind of liked their 70s console TVs with the > weird plastic pedastal and the preposterous "zoom" button. Pffft. Foggy memories of that stuff. I think, when I decided to look at the sound problem I went over to that place on Bryn Mawr just west of Kimball, North Central. They used to be authorized Zenith, RCA, Magnavox and some others distributors. I ordered the service manual and when it came in I remember the guy behind the counter said I wasn't going to like it. Not sure if it was from Zenith or the Sams copy but it basically was a single "road map", folded out to like a 3'x4' paper that was more or less just a block diagram of the set. Very few voltage reading points and or waveforms. Most of it was covered in "gray areas" and he said if you think the problem was in one of those areas, Zenith wanted the whole module back for diagnostics. So I'm assuming at least through the mid 90's all the defective modules went back to them. Later on, after LG took them over and Phillips took over RCA, there was a mail order place to get modules in Indiana, pretty sure they were called PTS, a place that used to repair detent (mechanical) vhf/uhf tuners. After those became extinct, they went into the module repair/replacement business. Pretty sure PTS stood for Precision Tuner Service but after a quick google, they don't seem to be around anymore or have a historical mention. Might of been PTC, like I said, foggy memory of all that now. Anyway, with those Digital System III's (or whatever they were called), Zenith never wanted board level repairs on them. Just module exchanges. -bruce bje@ripco.com |
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