Looking for STV circuit diagram

Hi Team, my trusty 25-year-old STV has gone on strike. Maybe I shouldn't care but it still worked so well that I would like to try to get it going again. It is probably the last relic of a period when engineers in astronomy made stand-alone equipment and didn't make the laptop do it all. The issue appears to be centered around the power circuitry. It won't turn on and there is power to portions of the power supply but not all. I have my suspicions about one IC but need more information. I do hope whoever owns the IP isn't too precious now. If that's an issue I would be really happy with just the power supply diagram.

Regards Monte

 

Hello Doug and thank you very much for coming back to me. For a bit of background let me tell you the history of this unit. I live in Australia and was captivated when I read the S&T article about this device in about 2000. It was perfect for my requirements. Luckily I was in the US in 2002 and a friend was able to get me one. We met up in Vegas and he gave it to me in its black case in the lobby of a casino. God knows what the security staff might have thought of the handover. It can't have looked good.

It worked very well and was a hit at many outreach nights with its track and accumulate feature when I projected its output onto a wall and showed the public DSO's materializing with each frame. I needed to sell some astro equipment for family reasons in about 2010. However when I went to show it to a potential buyer I made the easy but fatal mistake of connecting a normal 12v power source to it. You may be aware that for reasons that only someone from SBIG could explain, it used a negative central pin on the DC jack. I connected it with reversed polarity and there was a puff of congratulations smoke and the buyer turned on his heel and left. I put it in the cupboard for another day. SBIG explained that D18 was probably burnt out. It was. It was installed specifically to run power through a fuse in the case of what I did. As per Murphy's Law the diode and some PCB track sacrificed themselves to save the fuse. I didn't have much experience back then with SMD devices but managed to replace the diode and it has worked well since then. The repair is ugly but effective (see blue circle). The screen died at the same time by coincidence or as a result of this outrage I authored. It was replaced with a reverse camera screen from Ebay and a bit of 3D printing for a bracket. I hadn't used it for a couple of months and when I went to test something this week it wouldn't wake up.

The image shows the area in question. I understand the corporate desire to protect IP but any schematics around this area that includes the components you listed would be a Godsend. I would also be especially grateful for test point voltages as the SBIG guys put a lot of them in and they can be super helpful. The central pin of the voltage regulator U50 (orange circle) is the common and it now has no voltage. It would appear it should as it powers LED 1 (which is not illuminating). I am suspicious of components within the red circle as they appear to feed the VR common pin.

I want to get a few more years out of this unit. It's probably one of the last ones standing and it represents a great period in electrical eng. that cheap computers have brought an end to.

Kind regards Monte

 

Thanks Doug this is very helpful. I will work my way through these voltages to see if the issue is hiding somewhere here.

Regards Monte

 

Good news. It appears that U52 is the culprit. It should be giving out 5v and its only giving out 0.5v. There could be an issue with C124 pulling it down to earth but the IC is more likely to fail than the cap. Thanks for your help. I'll keep you posted. Regards Monte