View Full Version : Helios II up and running PT-DOS!!!

May 9th, 2014, 03:33 PM
I finally sorted out my Helios II problem.

My drive was completely rebuilt by a friend who is an expert in Persci drives so I knew it wasn't the issue.

So first problem, my 32kra had a bad ram chip. When the system heated up it failed.

Next problem, the Helios front panel was causing a failure to boot. On advise, I created a special cable to bypass the front panel.

Finally I had a bad chip on the formatter card. It must have been marginal as it worked in another Sol-20 that belonged to a friend with a working Helios system. I've been thinking about this for the past hour and his system is an early unit without the T2 transformer and without the factory brown out mod so that could be the difference. My one system is a T2 and the other has the ECN specified modification.

Btw to find the problem on the formatter required me to write a program to convert a PTDOS image for DISKT to an ENT file so I could load it over a serial port into solos. There wasn't a copy anywhere on the internet that wasn't an image file. With DISKT, an oscilloscope and the manual I was able to track down what was preventing my system from booting.

Anyway I'm pretty stoked that it's up and running.


May 9th, 2014, 05:08 PM
Always exciting when a restoration project finally boots and runs. Good job!


May 11th, 2014, 03:09 AM
I've never seen a boot screen for PT DOS before. Brilliant!
Would be great if you made a youtube vid of PT DOS in action, and run through some of the basic functions. I would love to see that.


May 11th, 2014, 04:56 AM
I think the reason you haven't seen PTDOS in action is other than using an emulator, there really is only one person who know how to rebuild these Persci drives back to spec, and he does it as a hobby. I have noticed a lot of the Helios cabinets I have seen don't that those drives in them anymore. They have replacements and may not be able to read the Helios disks. Even the pic of the unit at the Computer History Museum in California looks like the drives were swapped for a set of Seagate drives.

I think this person has told me he has rebuilt 6 drives so far. I only know of mine and one other that are out of his care. So this is very exciting for me.

I still have a lot of cosmetics to get done on the unit. The case needs refinishing and I have to replace a couple of broken connectors on the controller and formatter cards. I found NOS connectors and will put stress relief pulls on the cables so the plastic doesn't break on the connectors, which seems to be a common issue with these type.

Anyway I will make some videos when it's all done in the summer. I plan on doing the cosmetics next month since the weather will be nice to take out the compressor and sprayer.


May 11th, 2014, 07:45 AM
That is so cool. The last time I ever saw PTDOS bootup on the SOL20 with Helios drives was at the NYC PC Expo in '77

May 11th, 2014, 08:55 AM
That's why I was so excited to get it working. PTDOS running on a Helios II with correct Persci drives is the "White Whale" of S100 floppy disk setups. My system came though a third party but was originally one of Jim Battle's of Sol20.org setups that he mentions on his site that he couldn't get running. That was also a few years ago. Since then there have been some discoveries on how to repack and rebuild the bearings in the drives and stuff like that.

I also didn't do the hard part. As I mentioned a friend rebuilt the drive. I just got the controller cards and Helios front panel fixed. Granted that wasn't easy, but it wasn't as hard as rebuilding a disk drive down repacking unobtainable bearings.

I also now know what I'm showing off at VCF next year :-)


May 14th, 2014, 04:19 PM
That's awesome. It' so rewarding getting something going again.