Thread
SE/30 horizontal sweep lines....still!
Well, I finally got around it and installed a new transistor, but I still get the retrace lines... what to check next?
I just checked for a heater (pin 3 and 4) to cathode (pin 2) short, but that fortunately wasn't the case.
Thats not anything. That is just noise. Your missing the video signal. A real signal is much greayer in amplitude, but it also contains the video signal for a line and has a front/back porch inversion.I was wrong on the fuzzy line stuff, I just hadn't set up the scope properly for such small data.This is what I got directly on the logic board, probe on pin 13 of the UG6 IC, the video data output:
The signal isn't all that strong, only around 100mV P-P.
This is the signal on the inputs of the 74LS38 IC on the analog board, due to a couple of resistors on the logic board, the amplitude is a bit less than the output of the UG6 IC, around 70mV P-P.
On the output of the 74LS38 I get the 1.5VDC, so I think I'll try the spare logic gate, maybe that one will work.
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.Thats not anything. That is just noise. Your missing the video signal. A real signal is much greayer in amplitude, but it also contains the video signal for a line and has a front/back porch inversion.I was wrong on the fuzzy line stuff, I just hadn't set up the scope properly for such small data.This is what I got directly on the logic board, probe on pin 13 of the UG6 IC, the video data output:
The signal isn't all that strong, only around 100mV P-P.
This is the signal on the inputs of the 74LS38 IC on the analog board, due to a couple of resistors on the logic board, the amplitude is a bit less than the output of the UG6 IC, around 70mV P-P.
On the output of the 74LS38 I get the 1.5VDC, so I think I'll try the spare logic gate, maybe that one will work.
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 for this kind of signals):
BTW, you can right-click the images and choose to view them in a new window or something to get a bigger version.
After that I went on to measure the vertical sync on pin 14 of the UG6, which is a 60Hz pulse train which sounds plausible, so I assume that one is correct as well.
While I was at it I also measured the vertical sync on pin 18 of the UI6, which gave a nice 22.3kHz square wave:
So... it seems UG6, the composite-video-creation IC doesn't make a video signal, which causes this nasty pattern on the display. Is UG6 the one I should replace (anyone with a scrap board who can unsolder it for me?) or is there a possibility something else is causing this?
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 for this kind of signals):
BTW, you can right-click the images and choose to view them in a new window or something to get a bigger version.
After that I went on to measure the vertical sync on pin 14 of the UG6, which is a 60Hz pulse train which sounds plausible, so I assume that one is correct as well.
While I was at it I also measured the vertical sync on pin 18 of the UI6, which gave a nice 22.3kHz square wave:
So... it seems UG6, the composite-video-creation IC doesn't make a video signal, which causes this nasty pattern on the display. Is UG6 the one I should replace (anyone with a scrap board who can unsolder it for me?) or is there a possibility something else is causing this?
Has nobody got an idea?
can you post a picture of what is acutely displayed on your se/30's CRT?
I knew your horiz and vert signals where good otherwise you would have no raster.
You need to stare at the SE/30 schematics for the video section and find out where the video bitstream from the vram mux serializer gets lost.. and check the traces. If good, replace the IC.
You need to stare at the SE/30 schematics for the video section and find out where the video bitstream from the vram mux serializer gets lost.. and check the traces. If good, replace the IC.
Here's a quick pic:
I'll check those muxes and the video signal from over there, hopefully I'll find something useful.
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.
So you can rule everything out from there on back.. now you need to look forward.
You can start by cutting the video signal wire going from the analog board to the main logicboard. This will tell you where to start looking. Im thinking shorted capacitor somewhere, as you have no signal but bad dc-offset biasing your tube on...
You can start by cutting the video signal wire going from the analog board to the main logicboard. This will tell you where to start looking. Im thinking shorted capacitor somewhere, as you have no signal but bad dc-offset biasing your tube on...
And you already tried swapping the video board with a known working one?
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!
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:
Pull the datasheet of that ic and make sure all your truth table conditions are met first...
because i get that same screen , when the video board goes bad with the se.
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. ;-)
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 high.
Pin 15 is high, but "pulsed" low at a rate of approx. 2MHz.
...But I can't see on myself if this is all good or not.
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 to make and for shorts, but everything measures fine. What could this be?
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 to make and for shorts, but everything measures fine. What could this be?
There is either bad VRAM, or one of your muxes that loads up the VRAM is got a broken trace. your VRAM is missing information. So either the data coming from it, or going to it, is missing databits.
Reason? Bad VRAM, or more likely, bad trace.
Reason? Bad VRAM, or more likely, bad trace.
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! 
Here you can see it is displaying the "you did not properly turn the computer off last time" message in Dutch:
I'm glad I finally fixed it!
Thank you very much techknight for pointing me in the right direction! You deserve a pat on the back. :I
Here you can see it is displaying the "you did not properly turn the computer off last time" message in Dutch:
I'm glad I finally fixed it!
Thank you very much techknight for pointing me in the right direction! You deserve a pat on the back. :I
hey man good find.. so pin 10 on the Vrom to pin 4 on the UD8, man your cap goo must have been extra bad!
so you think this and the I/C you replaced and this bridge wire from vrom was the fix here?
so you think this and the I/C you replaced and this bridge wire from vrom was the fix here?
Yeah, aside from a lot of probing and measuring those two things finally did it.
The cap goo was indeed very hungry! :-x
pretty nice man!
Well i knew something was up soon as I seen that scope shot.
Glad you got it working.
Glad you got it working.
Congrats! Another one saved 
i just fixed SE/30 just now with a dead 74LS166
the cap goo seems can short them out… and they go bad.
the cap goo seems can short them out… and they go bad.
That's great to hear!
i need to add "10 on the Vrom to pin 4 on the UD8" another variant of SE/30 screen diarrhea. shot gun fixes are cool!
shot gun fixes are cool!