twistedpneumatic
Experienced Member
I went back to approach fixing my PET again. This is where I'm at currently.
I installed 3 new ram chips and their sockets.
PETTEST2.BIN is installed.
As you claim it should...the signals are all 5V until about ~6s after it boots of which VSYNC is about 4.4, HSYNC is around 3.5V, and 0.3V on Video-IN. Seems normal enough...so I think I can conclude the board is atleast partially functional. Maybe V-in should be higher...but it seems as the CRTC is being initialized so I don't think its much of an issue. I could always disconnect the resistor to the grid to see if a raster forms.
Anyway...based on that I measured around the CRT board. Got proper voltages on the cathode(glows), HYOKE and VYOKE coils, along with proper voltages on E18, E30, E400, and the -115V rail once HSYNC kicked on. The only voltage so far that has come up wrong is Q761(by R762 on zimmers-321448 schematic), where the base never comes back down to 12.9V, rather stays at 18V. Other transistors on the board do similar but kick down once HSYNC comes in and the HOT can start generating voltages.
So the tube currently does this: The tube starts glowing...a dot appears on the screen, eventually gets quite bright over a second or two. The beam drops down and a raster that makes the entire width and about half the height flashes then it dies. I've found the tube to make a sorta crackling sound...I had an old trinitron that did this so I think its the HV discharging? Also some slow motion video on my phone....I heard the while from the CRT since it was slowed down by 8x, and it was stable for a teeny bit, then start to wharble or something...sounded...unhealthy? Anyway the raster appears(1 run) and the picture dies. No more dot even. I'm suspecting loss of HV....though the grid voltage is on which would also cause that.
I'm lost on where to go now from here. I'm still betting on the CRT being bad....I showed the video of it running to someone at VCF and they said caps on the tube. I checked them with my multimeter and they mostly seemed good. I'm confused on where to go from here though.
I installed 3 new ram chips and their sockets.
PETTEST2.BIN is installed.
As you claim it should...the signals are all 5V until about ~6s after it boots of which VSYNC is about 4.4, HSYNC is around 3.5V, and 0.3V on Video-IN. Seems normal enough...so I think I can conclude the board is atleast partially functional. Maybe V-in should be higher...but it seems as the CRTC is being initialized so I don't think its much of an issue. I could always disconnect the resistor to the grid to see if a raster forms.
Anyway...based on that I measured around the CRT board. Got proper voltages on the cathode(glows), HYOKE and VYOKE coils, along with proper voltages on E18, E30, E400, and the -115V rail once HSYNC kicked on. The only voltage so far that has come up wrong is Q761(by R762 on zimmers-321448 schematic), where the base never comes back down to 12.9V, rather stays at 18V. Other transistors on the board do similar but kick down once HSYNC comes in and the HOT can start generating voltages.
So the tube currently does this: The tube starts glowing...a dot appears on the screen, eventually gets quite bright over a second or two. The beam drops down and a raster that makes the entire width and about half the height flashes then it dies. I've found the tube to make a sorta crackling sound...I had an old trinitron that did this so I think its the HV discharging? Also some slow motion video on my phone....I heard the while from the CRT since it was slowed down by 8x, and it was stable for a teeny bit, then start to wharble or something...sounded...unhealthy? Anyway the raster appears(1 run) and the picture dies. No more dot even. I'm suspecting loss of HV....though the grid voltage is on which would also cause that.
I'm lost on where to go now from here. I'm still betting on the CRT being bad....I showed the video of it running to someone at VCF and they said caps on the tube. I checked them with my multimeter and they mostly seemed good. I'm confused on where to go from here though.