Need help with a macintosh performa CRT - Page 1
Forum section: electronics / projects

author: TRS-90
author_rank: Regular Contributor
timestamp: April 24, 2016, 02:44:01 am
content: I have a macintosh performa 577 that has a busted hard drive so I cant use it as a computer, but the CRT still works so I would like to attach a composite input to it.BUT, there is NO driver circuitry inside! From what I could find (which was very little) the CRT is controlled entirely in software on the motherboard and since I don't have a lot of high tech equipment (aside from a multimeter, a computer and a cheap soldering iron) I cant find the inputs or source of the video signal.If anyone could help me find the schematics or help me make a video driver circuit by providing a parts list then I would be very grateful.Also the CRT board is a power supply from what I could see when I took it apart.(sorry for the long post)

author: TRS-90
author_rank: Regular Contributor
timestamp: April 24, 2016, 05:26:39 pm
content: Okay I forgot some information.The CRT is a Sony Trinitron 14 inch (however on 13 inches are visible from what I heard).The computer also has a weird power on system which only powers on the motherboard (the CRT is on when to flip the power switch) when you press the designated power key on the keyboard, which is a problem since I want to use the 5 an 12 volt power connectors on the harness but they don't have any power going to them, I checked!So how is it able to soft power on?!?Anyway that is what I forgot to put in on my original post.

author: helius
author_rank: Super Contributor
timestamp: April 24, 2016, 05:51:27 pm
content: Macintosh models with ADB keyboards use a dedicated pin of the ADB cable to start the power sequence. This pin is directly connected to the keyboard's power key (labeled with a thin isosceles triangle). On many models power for this pin comes from a battery, so the machine won't start when the battery is dead. On others there is a standby 5V supply that is always active, similar to the ATX design. When the power supervisor is set to the on state, it releases a disable signal to the PSU which allows it to turn on (exactly the same as ATX). This provides software power control and scheduled activation from the real time clock.You are mistaken about the CRT being driven from the mainboard. There is no flyback or horizontal output transistor on that board and it is not produced with isolation required for CRT voltages.

author: TRS-90
author_rank: Regular Contributor
timestamp: April 24, 2016, 05:57:00 pm
content: Oh, I did not know that.I am not experienced in the world of TV technology but I am willing to learn in this case.Is there a way to get a composite in put to the CRT in any way?I would like to put a game console in the case and use the original CRT inside the system but I can't find where on would put the wires to do that.Thanks for the info on the power on system used by the way.

author: helius
author_rank: Super Contributor
timestamp: April 24, 2016, 06:14:40 pm
content: There is no composite decoder as far as I know: it uses RGBHV signals. Some models of these machines did have TV input (RF), and since the boards are easily swapped you could put one in.

author: TRS-90
author_rank: Regular Contributor
timestamp: April 24, 2016, 06:23:33 pm
content: I sort of guessed that they had RGB with the colored wires but I wasn't sure.Also I tried to find one of the Sony Trinitron 14 inch CRT boards but I couldn't find one.But swapping the boards presents an issue in regards to the power supply, see I would like to use the original power supply to power the game console I want to put in this machine, though I could possibly rig a power supply on the new board in some macgyverish way.Also is there any way to make the new board default to composite in without having to use the buttons.I would like it to be more of a monitor type deal than a TV in terms of plug and play (or solder and play in this case).Thanks.

author: TRS-90
author_rank: Regular Contributor
timestamp: April 24, 2016, 06:47:25 pm
content: WHOOPS! I did not realize what you meant until I read it for the 3rd time or so!Well in this case would a macintosh perfroma 577 from 1994/95 or a macintosh LC580 have one of those RF inputs?(those are the computers in close enough manufacturing types I have on hand at the moment)Also the first arcade game used a TV with a composite mod on it because the TV originally had only RF in on it so I could do that if I can find the info on it.Sorry for reading it wrong.

author: Kilrah
author_rank: Unknown
timestamp: April 24, 2016, 06:56:48 pm
content: Quote from: TRS-90 on April 24, 2016, 06:47:25 pmThat's an easy mod though given that the output of the RF demodulator IS typically composite. In your case of converting composite to RGBHV it's a whole different matter, especially if you're unlucky and whatever scan rates the monitor expects aren't in a range that matches video.

author: TRS-90
author_rank: Regular Contributor
timestamp: April 24, 2016, 07:01:49 pm
content: Okay that mod should be easy to do (I hope I can get the inputs right).The CRT used in this computer is a standard sony trinitron tube so it should work with the composite signal just fine as far as I know.Any tips on finding the RF part of the CRT driver board in the computer or what the internal power supply is rated for?

author: TRS-90
author_rank: Regular Contributor
timestamp: April 25, 2016, 08:59:30 pm
content: I did some research on the power supply and found the rating in the service manual.PSU: 120-240V universal 120 wattsBut even in the service manual I couldn't find hardly any information on the analog board inside this particular computer.Meaning I can't see if it has one of those RF sections and I didn't look for it when I opened the case because I did not know it was there.Are the schematics anywhere on the internet because I can't find them.

author: helius
author_rank: Super Contributor
timestamp: April 26, 2016, 01:02:53 am
content: It's a typical compact CRT board with added voltage regulators for the computer. The RGBHV signals go through a wire harness from the main board's pin connector, to the socket on the analog board. You could identify the pins being used by tracing backwards from the adjustment potentiometers at the rear panel, to the pins at the edge. The specific pots are labeled 'RR', 'GG', and 'BB', and control the amount of drive added by the three video amps.Be careful and use correct service procedures if you want to reverse engineer the analog board, since there are lethal voltages present, even when the machine is unplugged.

author: TRS-90
author_rank: Regular Contributor
timestamp: April 26, 2016, 02:05:09 am
content: So if I'm reading this right, if I trace the wires back to the adjustments panel or a little past/before it and hook up some component cables to the wires and turn on the CRT I would get a signal? or would I have to do some more stuff in regards to the deflection coils?(The game console I plan on using probably has a component cable adapter for it)Also is there a way to make the power supply turn on automatically? It would make the console easier to hook up that way.Thanks again

author: TRS-90
author_rank: Regular Contributor
timestamp: July 25, 2016, 07:27:21 pm
content: I hate to revive a post that has been so dead for so long but I wanted to see if I could do this post justice for once.The board I am dealing with: PCBF ANALOG BD LC520/LC575/MACTV 820-0582-AIt has ALL the connections I need but I DON'T KNOW where they go on the board and I don't know a way to safely test the pins without damaging something on the board.The connector has 40 pins on it. I assume 4 pins for the microphone 15 for VGA video and 2 for the power on system.I cant fathom what the rest would do.There IS a constant +5V coming from the power supply.CAN WHO WORKS AT APPLE OR HAS A COPY PLEASE HELP ME FIND THE SCHEMATIC!I specified the model above.End of line.