Metrix 803B Oscilloscope power supply issue

[stj]

Re: Metrix 803B Oscilloscope power supply issue

i suspect it's the startup capacitor,
and it's only about 10p to find out.

[itsthatidiotagain]

Re: Metrix 803B Oscilloscope power supply issue

I have every sympathy with your Google allergy. I posted there because I didn't want to clutter up this forum, and Google tends not to mash the original images up *too* much, or impose limits on their size.

I plan on getting some better pictures of the PSU board in particular, this evening. I'll make sure that as many of the markings on the componets as possible are legible. If I have the time I might unsolder the mains input wires and pop the silkscreen side on my flatbed scanner too, in case I have to reverse engineer from the PCB.

While I had it in bits, I spotted an un-connected single row of header pins, on the main PCB, which I suspect are for the "RS232 Serial" option (the case also has a punchout next to the 25 way D one, for what looks very like an IEEE connector, but there is no mention of that anywhere on the manufacturers site).

If I manage to coax the thing back in to life, I will take a crack at seeing what the signals on that header connector look like.

My gut geeling is that the serial option is probably a very expensive 25 'D' type on a bit of flat ribbon cable, with some equally expensive software to drive it.

However first on the list of things to do is identify the 8 pin chip beside the 400V cap and the two other chips that look suspiciously like opto couplers nearby. I'll see if I can also identify the "transistor" on the black heatsink.

Armed with that, and the values of some of the other eletrolytics, and passives you never know... it might not be such a poor investment after all.

[stj]

Re: Metrix 803B Oscilloscope power supply issue

upload the foto's, that google shit gives me a headache trying to see the foto's fullsize.
and what is the part number on the 8pin chip near the big capacitor?

[itsthatidiotagain]

I'm looking for a bit of advice or better yet a schematic for a Metrix 803B oscilloscope.

The 40MHz animal here...

.. I picked one up for very little on ebay, and it looks quite a useful thing to have around.

The listing stated that it was dead, but in clean condition, so I took a gamble that it might be something simple.... needless to say it wasn't the fuse or the mains switch, and the next logical step is to check the power supply.

Naturally I can find no schematic on line for it, so before I start to reverse engineer the thing, I wondered if anybody else had a schematic, or access to another 803B to compare.

Everything looks clean and there are no obvious crispy bits or popped or bulging caps. When I power on, the mains gets from the power jack board, through the mains switch and over to the PSU board, and appears at the input side of the switch mode supply. Thats as far as I have probed so far, other things keep getting higher priority.

I dont appear to get any audible high frequency squeak from the switch mode transformer or static on the tube, at start up suggesting it might be fairly simple to track down, but before I actually start to get my hands dirty I thought I would ask around in case the fault is a well known issue that someone here has enountered before.

An incomplete set of pictures of the innards of the poor beast complete with optional dust are available here.... and yes, I know that the fuse is missing in some of those pictues, I had popped it out to test it. I did remember to re-fit it.