Recent content by Mark_W

No, only LC III and LC 520/550 has onboard vram. There's no activity on scsi bus at all? You can also try to insert a floppy disk, see if it tries to boot from floppy drive.

Is VRAM installed? LC II has no onboard VRAM and if no VRAM is installed, it will boot to a blank screen. Also try a different VRAM stick. Also plug in a hard drive or bluescsi and see if the motherboard tries to boot from it.

So like I said primary side should be ok, if you see around 10v across pin 4 and 6 on TDA4605 then it should try to start, and you should see the switching signal on mosfet's gate with an oscilloscope. You should also see DC voltage on secondary side as soon as the power supply starts, but seems...

Did you short BD11 when taking these measurements? If so and voltage across pin 4/6 is still 0 then you found the problem. Soft power control for logic board psu isn't working, and you need to fix it first. Considering there are only 3 transistors and 1 optocoupler (CNY17-3) in the circuit iirc...

Yes basically what @jonschultz said, you are measuring the voltage regards to cold ground which is floating, you need to measure voltage across pin 6 and pin 4 on TDA4605. Like I said, you need to verify whether QP11 turns off after receiving power on signal from logic board, and whether...

53.8v is way too high, should be around 10-20v IIRC. Also ip7 is on primary side so you need to measure the voltage of it regards to hot ground, not cold ground.

Power supply for CRT part and logic board are mostly independent, and from your readings the CRT part should be working fine. 5V standby voltage is generated by CRT part and it's present so we can rule it out. You can jump start the logic board power supply by shorting BD11 with a jumper. If...

So both analog board and logic board have issues. I'd figure out the problem with analog board first, wavy pattern is usually a telltale sign of bad capacitors, if you have already recapped it, double check your capacitors. Also check 5v/12v voltage output on hdd power plug, as well as 31v...

DL21/22 voltage is ok, but DF2 voltage is much higher than it should be (8.2V). Did you install the correct zener diode? Also double check those power resistors and caps nearby, make sure you didn't install anything wrong.

Does the High-res card actually support 512x384? On this site 512x384 is listed as not supported: https://vintageapple.org/gamba2/vid-mon-matrix.html

If the front bezel says "Macintosh SE" and it's on the lower right corner then it's really an SE. If the "Macintosh SE" text is on the left then it should be an SE30 case, "/30" might be sanded off or faded for some reason, I've seen a few SEs without any text on front bezel before. Also...

The screen geometry and color are both way off which is a good hint that something's wrong with secondary voltage outputs from CRT transformer.Start with checking all voltages on CRT side, make sure 24V, 8.4V from transformer output are normal, as well as regulated 18V, 8.2V from zener diodes...

If you want an all in one boot disk, you can try macpack here under preinstalled macos images: https://mega.nz/folder/8hA3AQCJ#pWUq92L70yDXlogy9lk5Dg It contains system 6.0.8, 7.0.1, 7.1.2 and 7.5.5 iirc, and also thousands of classic software and games. I've used this image in an external...

Ok so I finally have an original LC to play with, friend gave it to me for repair, although it looked fine but leaky caps has done some damage to it. One trace from VRAM socket to cultdac is open causing very minor screen artifacts at 256 color mode, mc34119 amplifier is also dead resulting in...

Bought a whole lot of CC II/LC520 and LC475/575 boards from a forum member and been busy repairing them last weekend. Figured I might make a thread here and log my findings. LC575 - 1: Entire board is covered in electrolyte, especially the section near battery so I guess it's been battery...