Thursday, April 5, 2018

Yet another Star Rider repair

Would you use ice to find a troublesome part on a large board with a lot of generic TTL ICs?  Wise people wouldn't.  I may not be a wise person.

Monday, March 26, 2018

Isolation transformer and AC power

I found this old conversation with Mitch Schleiss about AC power and isolation transformers.  Posting it here so it gets preserved.

A lot of the old monitors have what we call a "hot chassis" meaning the metal frame portion is directly connected to 110vac.  If you were to touch it and ground yourself, meaning the ground plug on an outlet and/or a metal pipe in your house, you would be shocked by 110ac.  If you were to touch the metal frame to a ground, you would probably blow out a transistor or diode.  You need an isolation transformer which just has the same amount of windings on both the primary side and the secondary side to give you that 110ac in and 110ac out.  Seems like a dumb transformer but what it does is that there is no direct connection between the house wiring and the monitor: "isolated"  They are harder to come by now a days but is really needed for safety and component protection.  I have worked on monitors without it but you need to really understand what is going on!

The monitor is not connected to the ground at all.  The problem with the term ground is that it means too many things.  There is the power supply ground-referenced to the 5 volts. There is the FG or Frame Ground or sometimes called Floating Ground which usually means the Ground to the round plug on the ac outlet which should connect to the actual earth ground. and some others too.

In the days of arcade games, you would find switching power supplies with the ground and the FG connected together.  This is wrong and could cause all kinds of issues beyond safety like ground loops and audio humm.  The 2 spades on an ac plug are actually a hot and a neutral (which is actually the same as earth ground) but most people who wire up your house are morons and dont care which one goes where as it is just AC to them.

The ground on an ac outlet is really there for safety.  It is made so if something goes wrong, it is supposed to bleed off the power to ground instead of THROUGH you. More of a UL safety law here in the states.  That is why you see things like laptop power supplies with no ground.  THey are completely covered in plastic and thus you can not touch anything that is HOT even if it malfunctions.

My added notes:

Looks like you really can touch either side of the AC output of the isolation transformer and not get shocked!

Yes, I am touching the metal here. Yes, it is powering the light bulb. Yes, I am not getting shocked.

Touching both sides at the same time would likely shock one.  I am not going to attempt it.

The frame of my G07 is not connected to either AC input wire.  Therefore, I believe it should indeed be connected to earth.

Sunday, March 25, 2018

Dexter now support ALG multi-ROM

If you've enjoyed the ability for Merlin-Dx and Dexter to let you switch between three games (Dragon's Lair, Space Ace, and Dragon's Lair 2) then you may be excited about this new free update to Dexter which will allow Shaun Wood's ALG multi-ROM to tell Dexter which laserdisc image to load!

Saturday, March 24, 2018

Exploring a 110V AC outlet solid state relay


Needed for a future project, I had a hard time knowing how these things are supposed to work.  Most youtube videos I watched assumed that the wiring was obvious and didn't explain it.  I decided to find out for myself.

Tuesday, January 2, 2018

I think I finally understand how Star Rider's manchester/biphase decoder works

I've been scared to dig into one of the Star Rider schematics, the one with the "biphase" decoder on it.  This circuit is how it grabs the picture number from the laserdisc video signal, and how it also decodes the other biphase (aka manchester) data that exists on the disc.

I've put verbose comments on the schematic page so that I never forget what I've learned.  I hope someone finds it interesting as this represents somewhat of a victory for me :)

Since the jpg is large, I've hosted it on my wiki.  Click here here to view.

Tuesday, December 5, 2017

Star Rider VGG Repair (corrupt video)

Yet another Star Rider repair video.  This time it's a VGG board with problems.

Monday, December 4, 2017

Star Rider Biphase data captured from a real laserdisc and real laserdisc player

I hooked up my PR-8210A to Star Rider to get some accurate captures of correctly decoded biphase data.  Hopefully this is one of the last times that I need to use the PR-8210A for research!

Here's the captures that it took.