Monthly Archives: August 2017

DECstation 5000 Model 240 H7878 Possible Fault Found

Posted on August 28, 2017 by rjarratt

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

Posted on August 27, 2017 by rjarratt

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

Posted on August 26, 2017 by rjarratt

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

Posted on August 19, 2017 by rjarratt

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

Posted on August 13, 2017 by rjarratt

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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