Category Archives: Retro-Computing

VAXmate Flyback Transformer

Recently I fixed the power supply of my VAXmate, but found that there was a problem on the monitor board, which may be what caused the power supply to fail in the first place. My suspicion immediately fell on the … Continue reading

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MicroVAX 3100 Model 95 Power Supply

I have a MicroVAX 3100 Model 95 that I acquired some years ago. At 32 VUPs it is one of the faster MicroVAXen. Some time ago I stopped using it because memory modules would suddenly stop working. At the time, … Continue reading

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VAXmate H7270 PSU Fixed, But No Video

In previous posts I have been describing my attempts to find a fault in the H7270 power supply of my VAXmate. After a long time studying and testing it I finally found the fault. It was a shorted diode (marked … Continue reading

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Partial Re-cap of H7109-C PSU for a VAXstation 4000 VLC

Recently I had occasion to dig out one of my VAXstation 4000 VLC machines. Before using it I decided it was prudent to check the power supply, a H7109-C, to make sure there were no leaking or bulging capacitors. It … Continue reading

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Memory for a DECstation 2100

Recently I bought a set of 8 memory modules that were advertised as “DEC VS4000”. They had a part number of 50-19464-02. This is one of the modules: I had assumed this was for the VAXstation 4000 VLC, but it … Continue reading

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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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