Category Archives: Retro-Computing

H7874 Power Supply

The H7874 is the power supply¬† used in the BA4xx and R400x enclosures, such as several machines in the VAX 4000 series. I have a VAX 4000-500 in a BA440. I had some problems with this power supply that seemed … Continue reading

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Further Analysis of the VAXmate H7270 PSU Failure

I have been doing further analysis of the failure of my VAXmate’s H7270 PSU. To start with the schematics are now greatly improved. I am still not sure how correct they are, but here are the latest and greatest: I … Continue reading

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Possible Cause of VAXmate H7270 PSU Failure

Now that I have acquired a DSO (a Rigol DS1054Z), I have been doing more work to understand the failure of the H7270 PSU on my VAXmate that I first blogged about here. I still don’t fully understand the problem, … Continue reading

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VAXmate PSU (H7270) Failure

While I was using my newly working VAXmate the other day, it suddenly failed. I had left it running for a few minutes and when I came back there was a smell and the machine was not running. I wondered … Continue reading

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VAXmate

I acquired a VAXmate earlier this year. The VAXmate was the successor to the Rainbow. It is PC compatible and runs MS-DOS. It was the first commercial diskless PC, although mine came with an expansion box containing a Seagate ST225 … Continue reading

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MUSL Compiler Builds a Simple MU5 Program

I have been slowly working on getting a MUSL compiler that targets the MU5 emulator, with the ultimate goal of compiling the MUSS source code to run on it. The first step is to build a cross compiler that works … Continue reading

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Teletype Model 33 ASR Ribbon Feed

In November last year I attended DEC Legacy 2018 and as usual I took along my treasured Teletype Model 33 ASR. I hooked it up as usual to the PDP10 simulator in SIMH to run DEC’s TOPS-20 operating system. You … Continue reading

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