Another DEC Rainbow 100+

I recently acquired another Rainbow 100+. Here is a picture of it:

Rainbow 100+

The badges are on their side because this was installed in a vertical enclosure.

This came about because a little while ago I was given a Rainbow, and the person who gave it to me had a second one that he was going to keep. He told me that he wanted the vertical enclosure for his machine, like the one below, which happens to be one that I passed on to someone else some time ago:

Vertical Enclosure for a DEC Rainbow

When the opportunity arose to buy a Rainbow in a vertical enclosure I let him know. He wanted the enclosure but not the machine inside. So we agreed that I would contribute to the cost of the purchase, take the Rainbow itself and he could keep the enclosure.

When I got it home it was in a pretty clean condition. It contains an RD51 hard disk, an RX50 floppy disk drive and a 192K memory expansion options, for a total of 320K memory. The VR201 is an amber version.

Before powering it on I visually checked the PSU, it looked fine. I then imaged the hard disk, just like I did with the previous Rainbow. Interestingly, the first attempt to read the disk failed completely. The disk span up quite happily, but the MFM emulator could not find any data. Cycling power seemed to fix it and I imaged it twice just to be sure.

I then installed the hard disk emulator in place of the hard disk and powered it up. Booting from the emulated hard disk brought up MS-DOS 2.11. The AUTOEXEC.BAT then took me into the Rainbow Serial Port Setup Utility (SETPORT) program. I found that the hard disk had WordStar 3.31 installed. At some point I will go back to that and remind myself what WordStar was like.

Anyway, I now have another Rainbow and another VR201 monitor, which is good in case I need some spares.

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More Leaking Batteries

I haven’t been very active lately because I have had to temporarily relocate my collection. While moving it back again I took the opportunity to reorganise things a bit. In doing so I came across the first two PC motherboards I ever bought. I found that both had leaking batteries. I have another machine, a DECstation 220 that has suffered as a result of the same kind of battery leaking, so I decided to remove these batteries immediately.

The very first motherboard I ever bought was a 286 board, with a Headland HT-12 chipset. If I remember correctly it had 1MB of memory.

The second board I ever bought was a 386SX board with an ALI chipset.

I have added these boards to the pile of things to get working. I am a bit behind at the moment with the fact, as mentioned above, of having to temporarily relocate the collection. I am still working on the TURBOchannel Extender PSU, a couple of ZX Spectrums and the DECstation 220. However, when I get a moment I will give these two boards a very quick spin just to see if they still work at all.

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Update on H7826 Power Supply Repair

It has been a while since I last posted anything about what I have been up to. However, I have been busy trying to find out what is wrong with the H7826 power supply out of my TURBOchannel Extender.

I received advice that there were errors in my method for checking activity on the primary side and that the fault could be on the primary side. I spent some time reverse engineering the schematics for the primary side. Not being an electronics engineer I may not have drawn this logically, and there will be tracing errors. I will update the images as time goes on, so by the time you read this it may have been improved, but don’t count on it. Unfortunately the part numbers are not labelled on the boards, so I have labelled photographs with part numbers that I have made up myself.

This is the schematic for the main input section.

This is the schematic for the 50-19530 daughter board, which I think is for Power Factor Correction.

This is the schematic for the 5019572 daughter board, which controls the switching transistors. This one was done by Matt Burke, I have added labels to a photo and filled in a couple of missing bits.

Further probing with an oscilloscope revealed that the 555 on the 5019572 daughter board was not oscillating, which means the switching transistors are not being switched. I then found that the Vcc input to the 555 was not rising above about 0.2V. So the next thing was to see why this might be.

Unfortunately, while doing the probing around the 555 I think I managed to discharge the large smoothing capacitors near the 555. Thankfully I had already turned the power off, but there was a sharp crack from the spark. I could not find any physical damage anywhere.

I took the 5019572 out to test it on the bench with a bench power supply. I found that it drew far too much current, the current limiter on the bench power supply happened to be set to 1.2A, and that is what it drew. Clearly there was a short. I suspected the 555, partly because of the spark problem. When I took it out I found that it was indeed shorted across Vcc and Ground.

I replaced the 555 and then I found that its output oscillated. However the current draw was still high and the other IC, the UC3842 got very hot. I checked all the resistors, diodes and capacitors for shorts and they all appeared to be fine, so I suspect the UC3842 is also bad.

I now have to order a replacement UC3842 and see if I can get the daughter board to work correctly.

I am not sure if the short (or shorts) have been caused by the spark I provoked. However, the fact that Vcc on the 555 wouldn’t go above 0.2V when the board was installed suggests it may have already been shorted, or the UC3842 was already bad, but of course I won’t know until I have the daughter board working again and installed back on the main board.

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Repair Progress on the H7826 Power Supply

I have been working on the H7826 power supply that came in the TURBOchannel Extender of my DECstation 5000/240. Normally, after a visual inspection, I will just apply power to see if a PSU works. This one, though, was not in a very good state, with a lot of dirt and corrosion, and bits of heat sink all over the board. You can see more details in my earlier post.

So, the first step was to clean it up and replace many of the electrolytic capacitors that are apparently known to fail. Most of the capacitors I removed were in the output area, although I did remove a couple of small electrolytics near the two big input smoothing capacitors. After removing the capacitors in the output area and cleaning it up it looked like this:

I did not find evidence of leakage, but the dark area under one of the capacitors is a bit suspicious. I tested the continuity around the dark area and it seems fine. I then replaced the capacitors and cleaned the corroded heat sinks as best I could. The results are in the pictures below:

So then it was time to see if the PSU works. I reassembled it, making sure the fans were attached, as well as the status LED. I applied power and….. nothing. I was disappointed, but not surprised.

I did some probing around to see at which point the PSU is failing. I found the voltage across the big smoothing capacitors was a healthy 330VDC or so, so they are fine (they were not fine on the H7878 in the DECstation itself). I then checked the primary side of the transformer and I could see a signal. However, when I checked the secondary side of the transformer there was no signal at all.

This could be a problem with the transformer itself, or something else after the transformer. It was impossible to check without removing parts, so I started by removing the transformer. Here is the board without the transformer (primary side on the right):

H7826 With Transformer Removed

In the two pictures that follow I arbitrarily numbered the pins 1 to 6 from left to right. This is the primary side, where the windings are 1-6, 2-3 and 3-4:

H7826 Transformer Primary Side

This is the secondary side, where the windings are 1-2, 3-4 and 5-6:

H7826 Transformer Secondary Side

While I was at it I got out a ringing tester that I made a while ago (thanks to a member of the classiccmp mailing list) to make sure that the transformer is working and does not have any shorted windings.

This is the result of the ringing test on pins 1-6 of the primary side:

H7826 Primary 1-6 Ringing Test

On the secondary side pins 1-2 and 5-6 gave this result:

H7826 Secondary 1-2 and 5-6 Ringing Tests

The other windings all looked like this:

H7826 Other Ringing Tests

I am told the latter result may be because there are insufficient turns on the windings being tested, and that these results show that the transformer is working and there are no shorted windings. That is a huge relief because I suspect that the transformer would be very hard to replace.

The next thing to check was the output rectifier. In circuit, one of the diode networks (an MBR 3045) appeared to show some shorts. That meant I had to remove them, to test them out of circuit. The problem here is that the rectifiers are screwed into a large heat sink and the parts around the heat sink make it impossible to reach the screws. This meant that I had to remove the whole heat sink. To make matters worse, the heat sink is fixed to the board by two pegs. I could not see how the heat sink was connected to the pegs

To do this I first had to de-solder the three diode network parts and the temperature sensor. Once I had done that I tried gently levering the heat sink off the pegs, in the hope that the heat sink was just held on the pegs by friction. Thankfully this turned out to be the case. I used a little bit of WD40 to help the process, letting it soak in first, and I soon had the heat sink and the 4 components attached to it out of the board. The pictures below show the pegs and the heat sink:

I used a Peak DCA55 tester to check the diode network parts and they seem to be working fine, so that is not the cause of the transformer not showing any outputs. When probing the holes in the board, the ones for the rectifier network nearest the output still appeared all to be shorted together, but I traced that to two low-value resistors, so that is not the problem.

So I am still stuck not knowing why there seems to be no signal on the output windings of the transformer.

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Imaging RD51 From a DEC Rainbow 100 Model B

I recently acquired a DEC Rainbow 100 Model B, with a working RD51 disk. The disk is running MS-DOS 2.11. I want to preserve the contents of the disk before it fails. A while back I acquired the MFM Emulator board designed by David Gesswein and built it. Mine is an older revision of the board and it works really well. I have also bought the later board but I have yet to build it.

I connected it up as you can see in the picture below. In this case I connected the floppy power connector to the emulator board, and of course the RD51 to the MFM connectors.

Imaging RD51 With Gesswein Emulator

You can see that the BeagleBone Black that runs the software is connected to a network cable. I use PuTTY to log into the BeagleBone Black over SSH and run the commands needed. To image the disk I used the following commands:

./mfm_read -d 3 --ana --emu /sd/<file>.dsk --ext /sd/<file>.ext --note "<description>" | tee /sd/.log

After that I shut the machine down, and discharge the reservoir capacitors with a resistor, just to speed things up. The later revision has a jumper for this I believe.

Now is the time to run the Rainbow from the emulated disk. To do that you just connect the MFM connectors to the edge connectors on the emulator board, connect the power and power up.

This however does not automatically start a disk emulation however. I have not set that up because I want to use it to emulate different disks at different times. So I still need the network cable to be able to login and run the emulation this time. The commands to emulate the disk for the Rainbow are:

./mfm_emu -d 1 -f /sd/<file>.dsk

Note that I have to use drive id 1 for this to work on the Rainbow. Here it is working:

Running Rainbow With Gesswein Emulator

The Rainbow thinks it has a hard disk, but really it is just an emulator!

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Corroded H7826 Power Supply

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 of it though is the H7826 power supply. A lot of the heat sinks have corroded, leaving metallic flakes all over the board, presumably capable of creating shorts.

In some areas there seems to be some traces of a liquid which seems to be holding a lot of dirt and some of the flakes that have come off the heat sinks. I suspect this could be leaked electrolyte from some of the capacitors. However, none have obviously leaked, although they are mostly in contact with the surface of the board, so they could have leaked from underneath.

I will have to source some new heat sinks and find a way to clean the board thoroughly, and probably replace all the electrolytic capacitors. Only then will I dare to try to power it on. In its current state it is just too risky.

I don’t think the pictures below really do the problem justice, but hopefully they give a flavour of what state it is in.

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Booting VAXen From The Network

Sometimes it is very useful to be able to boot a VAX from the network. The two most common scenarios are

  1. Your machine is diskless. As time goes on this is going to be more and more common as SCSI disks die out.
  2. You have a disk in the machine and you have the VMS media, but you don’t have devices to load the media from.

In these scenarios booting from a running instance of VMS is the easiest way to get your machine running, and the best bit is that you don’t even need it to be running on physical hardware. I use the wonderful SIMH emulator to run VMS, and I use it as the boot node for getting other VAXen running. You need your boot node to be in a cluster and then add the real VAX as a satellite to the cluster.

I am assuming that you have VMS running on SIMH. If you need to understand how to install VMS then Phil Wherry’s page is a great start. Some notes to consider when following these instructions follow:

  • Make sure you select to install DECnet Phase IV
  • You may want to include DECwindows support too if you want to run it on a real diskless VAX.
  • When prompted for the SCSSYSTEMID you can use the suggested value of 1025, which equates to a DECnet node address of 1.1. However, if you are likely to want to get on HECnet, or run this machine as part of an existing DECnet network then you may want to use another value. To set your node address as N.M, the SCSSYSTEMID is calculated as N * 1024 + M.

Once VMS is up and running, login as SYSTEM, register a DVNETEND and a VAXCLUSTER license. The first step is to set up DECnet, but this is only so that you can communicate between the boot node and the satellite using DECnet. To configure DECnet run @NETCONFIG. For the node address use the address that corresponds to the SCSSYSTEMID you used above, so if you used 1025, then enter a node address of “1.1”. You do not need the node to operate as a router (and you need to register a DVNETRTG license if you do). I then choose all the defaults when asked about accounts. Finally edit the SYSTARTUP_VMS.COM file so that DECnet is started automatically (uncomment the line START/NETWORK DECNET).

Now you are ready to setup the boot node as a cluster. To do this run @CLUSTER_CONFIG_LAN. Choose option 1 to ADD <node> to existing cluster, or form a new cluster, then choose to use the LAN for cluster communications. The cluster’s group number just needs to be a unique number with respect to any other clusters you may have, unless you want it to be part of an existing cluster. Select Y when asked if it will be a boot server (obviously, that is the whole point here). For the ALLOCLASS I used the second number in the node’s DECnet address (for address M.N, I used N for the ALLOCLASS).

After the machine has rebooted it is time to add the VAX as a satellite. Login as SYSTEM. I found I had to run the following commands, although I am sure I have not had to that before


Then run @CLUSTER_CONFIG_LAN, select 1 to ADD a VAX node the cluster, then select that the node will be a satellite. Give the node a name and an SCSSYSTEMID that translates to a DECnet address. The hardware address for the new node’s LAN adapter is its MAC address. Once the satellite has been configured, just start up the physical machine and tell it to boot from the network adapter.

There is a full transcript here.

If you have a local disk on the satellite then you can mount the disk and restore the basic VMS saveset to the disk. I then copy the remaining savesets onto the same disk, so that when I boot off the physical disk I say the remaining media is on the same disk. That is how I install VMS onto a physical disk from the network.


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