Author Archives: rjarratt

I recently turned once again to trying to get the DECstation 220 working. I have the original motherboard and a spare one. Both had battery damage and neither one works. The spare actually works less well than the original but … Continue reading →

I have a number of RF72 hard disks. These are 1GB DSSI disks (DEC rather grandiosely called them Integrated Storage Elements, or ISEs). Most of them work well, but I have one that will not spin up. The console firmware … Continue reading →

A few years ago I acquired a KDA50, which consists of 2 modules, the M7164 and the M7165, an RA72 disk, two RA70 disks, an RA60 disk drive, an operator control panel (OCP) and some big cables, with one I/O … Continue reading →

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 →