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did you end up fixing this Dehij ?

So I solved this problem. Was the flyback. I started testing in the contracts and brightness circuits given the visual changes when brightness was adjusted. All looked ok from a component perspectives I tested the output of the Contrast Pot on my scope and it showed a lot of noise, then...

I have narrowed it down to the brightness controls now (I think). See video, when brightness is increased so does the interference. I have checked most components in this areas and all look good, I have moved the Pot around checked continuity between components. I just need to check the two...

So I have done some more investigations, all electrolytic caps are now replaced on the analog board, DP3 and DP4, CNY17G, I have swapped TDA4605 and TEA2037A with another classic all without any changes. I have noticed that the MOSFET IRF740 in the large heatsink gets warm on this machine...

Well I thought I had it fixed. On Tuesday was all good, nice steady scene, nice clear sound. Turned it on this morning and there is "interference" ripples on the screen. So I tried the logicboard in a known working Mac Classic and it is fine so this new problem is on the Analog Board. The...

I have the same problem, what lead you to PP1 ?

Do you know the replacement Flyback is a working one ? You can test with a Oscilloscope if need be. Is the machine actually working and displaying anything ? Is there a noise inferring the crowbar circuit is being initiated ? I had a similar problem -...

I fixed this. Was a brown trace from Pin 1 of J12 that went past C8. It wasn't including C8 therefore impacted the 12v rail.

I can't actually any usage of the +12v on the schematic other than the output of the J6. So would this cause an issue with no booting to the beep and happy screen. If all chips are using +5v and that is reading ok can I assume the problem is somewhere with a trace ? I have checked about 40...

I suppose the obvious questions is the checkerboard likely a symptom of this or not related ?

thanks but what would pull it down to 1.8v if C8 is new ?

Hi all, I have a Mac Classic with a checkerboard pattern. I have recapped the analog and the logic board. I have proved the analog board works with a known working logic board (Board B) and I have proved the Logic board (Board A) also doesn't wok with the known working Analog board. The...

I always think it is safer to have the AB installed in the machine particularly with the anode cap (big red wire) safely connected to the CRT with the earth cable connected. Too risky for amateurs to be playing around some of these deadly voltages. Safety first folks, safety first...

I fixed this on the weekend with the summary being : I think the Flyback caused the issue with Q2 (Q3 US) (as per above) being burned out. When I replaced Q2 as per above the temp was rising quickly on a few components. When I used a Flyback from another 512K AB the temps were again stable...

See this link with the underlying problem - https://68kmla.org/bb/index.php?threads/240v-power-circuit.38381/

Hi all, can I use a 157-0121 Flyback from a Macintosh Classic AB to replace a Flyback on a 512k AB ? Same screen Clinton 5144.

Yes I did and great work. I think my problem is back at Figure 2 of the original doc though re the horizontal sweep and high voltage circuit.

Yes I did and great work. I think my problem is back at Figure 2 of the original doc though re the horizontal sweep and high voltage circuit.

I have progressed this a bit in the background. I have tried the logic board from the 512 with a known working Mac Plus analog board and all ok, I have then tried the working Mac plus logicbaord with the problematic 512k analog board and has the same problem, no video. I then tried using an...

all fixed and yes these were the capacitors that needed replacing, did all 4.