Author Archives: rjarratt

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →