SC1224 no vertical deflection

Troubles with your machine? Just want to speak about the latest improvements? This is the place!

Moderators: Mug UK, Zorro 2, spiny, Greenious, Moderator Team

User avatar
SainT
Obsessive compulsive Atari behavior
Obsessive compulsive Atari behavior
Posts: 141
Joined: Tue Dec 04, 2007 3:33 pm
Location: Gloucestershire

SC1224 no vertical deflection

Postby SainT » Tue Feb 27, 2018 2:27 pm

I'm after some help troubleshooting an SC1224 with no vertical deflection. I just get a single horizontal line.

So far I've found R731 was blown, I've replaced this and its blown again. So something is drawing a high current further down the line. D708 is the next thing to check going through the service manual.

If anyone has any experience with common faults with this monitor, that would be appreciated!

User avatar
SainT
Obsessive compulsive Atari behavior
Obsessive compulsive Atari behavior
Posts: 141
Joined: Tue Dec 04, 2007 3:33 pm
Location: Gloucestershire

Re: SC1224 no vertical deflection

Postby SainT » Tue Feb 27, 2018 3:12 pm

Forward voltage of 0.477V on D708 with multimeter testing. RPG10G has a forward voltage of 1.3V @ 1A. Even at pretty much zero current, it should be more like 0.6v according to the datasheets. Not sure if this is dodgy or not.... reverse is giving nothing, so it's not shorted.

User avatar
SainT
Obsessive compulsive Atari behavior
Obsessive compulsive Atari behavior
Posts: 141
Joined: Tue Dec 04, 2007 3:33 pm
Location: Gloucestershire

Re: SC1224 no vertical deflection

Postby SainT » Wed Feb 28, 2018 9:29 am

Sorted it! I managed to get the wrong fusible resistor to replace the blown one, I got 0.25w instead of 0.5w. I only noticed last night after looking through the schematics for ages trying to figure out what else could be wrong.

I replaced the blown one with a 0.5w FR2R2 as it should be and we're working again.

The issue was basically there was no power getting the the vertical deflection circuitry which is powered from the 24v line. That particular resistor was the fuse for the 24v line coming from the FBT.

It looks like a case of PCB component gunk becoming conductive over time and causing a short and blowing the fuse, as the blown fuse was well gunked from a nearby cap which covered a diode as well.

Another monitor saved from the tip! :)

User avatar
spiny
Disk Imager Supreme
Disk Imager Supreme
Posts: 2484
Joined: Mon Aug 11, 2003 11:53 pm
Location: just outside bristol
Contact:

Re: SC1224 no vertical deflection

Postby spiny » Wed Feb 28, 2018 9:44 am

nice work :)


Social Media

     

Return to “Hardware”

Who is online

Users browsing this forum: Bing [Bot] and 11 guests