Monthly Archives: August 2017

DECstation 5000 Model 240 H7878 Possible Fault Found

As previously reported, the H7878 PSU in my DECstation 5000 Model 240 has failed. Today I examined it more closely and I think that I know what at least one of the causes of the problem is. I started by … Continue reading

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DECstation 5000 Model 240 H7878 Power Supply Failure

When I first got the DECstation 5000 Model 240 I noticed that it would power off after a period of operation. This suggested a problem with the H7878 power supply. I had already inspected it for any obviously leaky capacitors … Continue reading

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DECstation 220 Monitor Sense Circuit Problem

Updated 2017-08-27. I was using a datasheet for the LM339 that was incorrect, the paragraph where I talk about the expected results has been changed accordingly. In my last post about the work to get my DECstation 220 working again I … Continue reading

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DECstation 220 Faulty Parts Found

I have been doing more work on the DECstation 220. As I commented in my previous post, it is only putting out a corrupted pattern to the screen because it is not writing anything to the video memory, apparently because the EMEM … Continue reading

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DECstation 220 Update

Previously I reported that I am now getting corrupted video out of the DECstation 220. I have spent the last couple of weeks trying to understand the problem, checking the tracks to all the chips in the battery-damaged area, on both … Continue reading

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