Anyone ever seen this happen to the DEF yoke connector? 128K
- Thread starter uniserver
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Yeah, this is mentioned on page 103 of Larry Pina's book. I also had an analog board with that kind of damage, but not as severe.
Pina says this happens when C1 shorts, sending high current through pin 4 of the J1 connector. Solution: replace C1 and possibly L2, as well as the connector.
Pina says this happens when C1 shorts, sending high current through pin 4 of the J1 connector. Solution: replace C1 and possibly L2, as well as the connector.
I would almost ALWAYS use a mylar film/orange drop cap in a deflection circuit. But thats just me.
Hey there, I know I'm a little bit late to the thread, but I had this same problem and my C1 cap looks fine. Sometimes my 512k makes a prolonged buzzing noise when the J1 connector is plugged in, other times it seems to boot like normal except the screen is dark. Any thoughts?
Did you measure the resistance through C1, or just do a visual check? Maybe it's failed even though it looks OK to the eye.
I just did a visual check for leaks/bulging. What's weird is that I used to be able to slap it a little bit to get video (hinting at a loose solder connection) but now no amount of slapping will bring anything on the screen.
Even if C1 is good, the charring on the connector could cause this as it doesn't make proper contact. I guess the high frequency signal could cause the buzzing noise. Replacing the wiring harness would probably be a good idea. I have the same problem with a Plus even with a new C1 cap.
Yeah, I'm going to try and scrape off some of the charred black bits and try to see if I can get the screen to work. What I'm wondering is what could have caused the meltdown in the first place? If the melting is caused by the C1 shorting, wouldn't that happen again?
Melting/charring/heat is caused by high current flowing through a high resistance. The resistance of the contact increased, causing it to heat up.
Why the resistance increases? Well bad connection mostly. Either the solder joint, or the metal pin itself starting to oxidize/corrode, This creates a higher resistance. The yoke still wants to consume the same amount of energy so the "resistor" begins to burn off heat.
Best solution: Cut off the yoke connector, unsolder the jack from the board and just direct-solder the yoke into place. Or, replace the connector if they can still be found.
Why the resistance increases? Well bad connection mostly. Either the solder joint, or the metal pin itself starting to oxidize/corrode, This creates a higher resistance. The yoke still wants to consume the same amount of energy so the "resistor" begins to burn off heat.
Best solution: Cut off the yoke connector, unsolder the jack from the board and just direct-solder the yoke into place. Or, replace the connector if they can still be found.
Thanks for the advice! So you're saying that most compact mac's J1 connectors can just start melting over time?
Depends on oxidation, the crusty solder joints, and the mileage on it. In theory, Yes... I fixed alot of these burned connectors in other electronics, like on power supplies for TVs, i have even seen ATX connectors do this.
I've seen this a few times, the worst case being on an SE/30 I took apart well over a decade ago. In Macs, it really doesn't seem to be that common; I've taken apart countless compacts and most of them still look OK, even if they had faulty analog boards. I believe the SE/30 I had was used heavily, as it was already in very poor shape by 1999 when I got it.
Ok so I cut off the J1 connector and replaced it with another one, I resoldered the other end of the J1 connector (as well as C1) and tried turning it on. All I get now is either a loud "BUUUUU" humming noise, or a booting beep and that humming noise. The screen still doesn't turn on. What do you guys think?
How about a recording of the noise? Is it a "flup flup flup" sound perhaps?
No, it's more of a "BNNNNNNNN" that goes continuously. I think it's coming from the actual CRT. Anyways, I just slapped the thing and I saw a flash of the "?" Screen. Also something new: when I slap the side, it sometimes restarts the computer and I get the startup bong but still no screen. Any clue why?
Ha! Something even weirder just happened: for some reason when I bend the analog board, the screen returns to normal! When I stop bending it (towards the side wall) it goes back to black! Any thoughts?
