Recent content by goerz

When I put the original Q12 from a good board the brightness issue is fixed. There are still other problems, though, because the screen flickers, and there is intermittent wobbling even with the good chip. I haven't tried putting BR103 in the good board because I'd prefer to limit the number of...

So I sourced this (relatively) expensive BR103 component, and nothing has changed: I still get a flupping set. R50 is back at the original 2.2KOhm. I put the original Q12 back, at least this way I can hear a nice startup bong, although the brightness is a bit random and the screen is wobbling. I...

Thank you, I'll search for one on eBay. Do you happen to know if the pinout of BR103 is reversed, the same way that of BRX49 is?

I'm resurrecting this thread because I have a problem with Q12 on an international board Mac Plus. I have a Mac Plus with a display that is too bright and the front brightness knob doesn't work. https://68kmla.org/bb/index.php?threads/blank-screen-on-recapped-macintosh-plus.44830/ When...

I did, using a donor board. No effect though... Next stop: replacing Q2. I've got a BU406 replacement on the way.

Ok so i tried with a spare flyback I had lying around and that didn't solve the problem. Then I swapped Q12 from the good board to this one and the excessive brightness went away! Also the front brightness knob came back to life. The problem now (besides finding a replacement for Q12 - this one...

Update: I have another working board, so I started swapping components. So far I have determined that it is not the CRT connector, resistor R5, nor the brightness control (variable resistor R56). Also, the good board works fine on this Plus, meaning that the problem does not lie in the CRT...

Wonderful, thank you! Let's hope this does the trick.

The top pin of the CRT connector, the one connected to C1 (that likely had failed) has signs of overheating, since it is darkened. Does a modern replacement exist?

Thanks, I will resolder everything then. It's going to take a while...

Yes, I recapped the analog board (240V version) completely (originally it generated a garbled screen), and I also replaced the U3 optocoupler. Initially it was a success: clear and steady image, bootup chime, stable 5V output. Then after a few minutes the screen went blank and the board started...

So i swapped R5 with a resistor from a working board and the problem didn't go away. Back to the working bench.

It doesn't work. The lines do disappear if the brightness control on the analog board is set to the minimum, but the image out of focus. Plus, the front brightness knob doesn't do anything.

I have a Mac Plus with the same issue. I read on the Dead Mac Scrolls that I should replace resistor R5 (470K ohm, 0.25 watt, 5%) on the analog board. I tested mine and it's 420K ohm: maybe it doesn't mean much, but the drop in resistance is still more than twice its 5 % tolerance. Maybe we...

I replaced C1 (which was leaking, by the way) with a 3.9 uf 450V film capacitor. This replacement has been tested on other boards I had been working on, so I don't think it can be the cause of the overvolt.