Recent content by SEthirty

That's great to hear! 8-)

Yeah, aside from a lot of probing and measuring those two things finally did it. The cap goo was indeed very hungry! :-x

After an our of probing I found that UK6, the video ROM, was missing a connection on pin 10 with UD8 on pin 4. I made a direct connection with a piece of thin wire, and... wait for it... it finally works! 8-) 8-) 8-) Here you can see it is displaying the "you did not properly turn the...

The journey continues... I've just replaced the 74LS166A with a 74HC166A, and it seems to work again! ...But only partially. We finally have video on the monitor again, but is is overlayed with a striped "jail bar" pattern: I've checked for continuity on all the connections the 74HC166A has...

Found a nice datasheet here: http://pdf.datasheetcatalog.com/datasheets/270/334520_DS.pdf On the first page you can see the function table; I could see parallel data on pin 4 and 5 with the scope, clock is running and power is OK. Pin 1 (serial) is tied to pin 9 (clear) and constantly held...

I assume you mean the neck board; I already checked every single component on that one, even replaced the transistor, but that didn't help. I also haven't got another one, so it is quite difficult to swap them. ;-)

Continuity is fine, but I get no output directly on pin 13 of the 74LS166, so I think I'll order a new one, and hope the Mac will work again! :beige:

Made some progress: there is no input serial video signal on pin 9 of the UG6, which should have come from pin 13 of the 74LS166... need to do a continuity test, but otherwise I think that 74LS166 is our culprit!

Just checked the outputs of the muxes, and... it looks like they work fine. I probed the mux output pins (7 and 9 of the 74F253's) on UC7 pins 9, 10, 11, 13, 14, 15, 16 and 17, but they all seemed to display serial data. Let's look further from there.

Here's a quick pic: I'll check those muxes and the video signal from over there, hopefully I'll find something useful.

Has nobody got an idea?

I've just checked all the rails of the PAL's, but they all were just fine. The UG6 chip got a approx. 15.3MHz clock on pin 1, which would be the system clock /2, so I assume that is correct. See it for yourself (it is far from a perfect square wave because my scope is too slow in digital mode...

Now that's some useful info! I'll check the power rails on the UG6 IC and linked components, maybe it just doesn't get its juice.

I just checked for a heater (pin 3 and 4) to cathode (pin 2) short, but that fortunately wasn't the case.

Well, I finally got around it and installed a new transistor, but I still get the retrace lines... what to check next?