Re: waveform at 555 + HV variance - amplifone monitor

Hi Karl,

You mentioned you installed "a Cinelabs type flyback". If you installed an
actual Cinelabs flyback, specifically a flyback with a Cinelabs warranty
sticker on it, then you are fully supported and we are happy to provide
specific assistance with troubleshooting your board. If you're replacement
flyback is a dud, we'll get it replaced.

If the flyback is a generic Cinelabs type (i.e. no warranty sticker), you
should contact the place you purchased the part, for technical and/or
replacement support.

Can you check to see if your flyback has a sticker on it?

Thanks,
-Mark

On Mon, Aug 13, 2012 at 5:29 AM, Karl Doe <karlcdoe@yahoo.co.uk> wrote:

> Hi all,
>
> Just a quick sanity check: Should the waveform from the 555 be a true
> square wave or do they vary a lot? I hooked up a dummy load (60w light
> bulb) across pins 1 and 9 in place of the HV transformer and connected a
> 'scope (10x probe, compensated) to pin 1 (ie the light bulb) and what I saw
> was a slow ramp up to the top of the wave (more like quarter of a sine
> wave) then a sharp cut off (more like what I expected), the frequency is
> still around 20kHz. I figure the data may be skewed because of where I am
> measuring it (or an effect of the lightbulb) and maybe I have to measure
> directly from pin 3 of the timer IC?
>
> Secondly (quite possibly related), I went ahead anyway and installed a
> cinelabs type flyback but I can hear occasional arcing and I think it's
> somewhere actually on the HV board. When this happens my HV probe shows a
> brief but significant increase in HV from, say 19.5 normally up to 25kV+.
> I can't decide if the arcing if the cause of the HV increase or if some
> other part of the circuit is playing up and therefore ramping up the HV and
> the arcing is just a side effect.
>
> So far all the electrolytics have been changed, +- 24v regs, 50 ohm
> resistors, 1n4001 diodes and the CR3 was missing so I used a sub. Old
> parts: the BU406D has not been replaced -tested okay as far as one can tell
> from the FAQ, and I haven't replaced the 555 timer.
>
> The output of the =- 24 regs is stable but a little out of spec on one
> rail like +2 volts or something with the lightbulb attached and I put this
> down to the 50 resistors. So logically speaking I think I shall replace the
> 555 timer, BU406D, and perhaps the frequency adjustment pot next.
>
>
> Thanks in advance.
>
> Karl.
>

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Received on Wed Aug 15 09:26:20 2012