Author Archives: rjarratt

Corroded H7826 Power Supply

Posted on October 23, 2017 by rjarratt

Now that I have got the DECstation 5000/240 working again it is time to move on to the TURBOchannel Extender that came with it. This is in a terrible state, with lots of corrosion all over the place. The worst … Continue reading →

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Booting VAXen From The Network

Posted on October 17, 2017 by rjarratt

Sometimes it is very useful to be able to boot a VAX from the network. The two most common scenarios are Your machine is diskless. As time goes on this is going to be more and more common as SCSI … Continue reading →

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DECstation 5000/240 Running Ultrix

Posted on October 13, 2017 by rjarratt

Having recently fixed the DECstation 5000/240 PSU, I wanted to see that the machine actually runs properly and can run an operating system. I had previously had another DECstation 5000/240, which I had swapped for something else, but I had kept the … Continue reading →

Posted in DECstation 5000/240, Retro-Computing | Tagged | 2 Comments

DECstation 5000 Model 240 PSU Fixed

Posted on October 1, 2017 by rjarratt

I have finally fixed the H7878 PSU from my DECstation 5000 Model 240. When I last posted about it, the PSU was not working very well, it was unable to sustain any load. Following that post I asked for suggestions … Continue reading →

Posted in DECstation 5000/240, Retro-Computing | Tagged | 4 Comments

DECstation 5000 Model 240 PSU Failing Under Moderate Load

Posted on September 17, 2017 by rjarratt

The H7878 PSU in my recently acquired DECstation 5000 Model 240 had a shaky start and then stopped working altogether. I found a problem with the input rectifier smoothing capacitors, at least one of them anyway. It was a real job to … Continue reading →

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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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