24-08-2017, 06:00 AM
(23-08-2017, 09:19 PM)Murphyv310 Wrote: One last thing, I don't really think beta is a big issue in the 2000, the transistor is acting as a switch and the drive should still be able to turn on a BU208 hard enough, if the beta is way too low it will overheat and fail within a few minutes, there could be lack of width or foldover left of centre on the picture before the transistor fails.
I didn't think beta was an issue in LOP transistors until I got caught out. In the Prowest monitor I was fixing there just wasn't enough base drive to saturate a BU208 at the right hand edge of the scan. It was in a separate EHT generator, much like the 2000, so there were no visible effects on the screen.. The symptoms were excess current consumption and the transistor getting hot. A careful look at the collector waveform showed what was happening. Normally the scope gain is turned well down to see the flyback pulse (about 200V on that design) but if you looked carefully at the baseline and turned up the gain you could see the collector voltage rising as it came out of saturation.
No way of knowing if the 2000 has enough base drive for a BU208 without trying it.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
