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Debugging an RX01/RX02 on an RX8E in a PDP-8/e

m_thompson said:
I use both DeoxIT® D-Series (D5S-6) and DeoxIT® Gold G-Series (G5S-6). I use the D-Series for cleaning and lubricating tin contacts, and the G-Series for gold contacts.
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Thx! Anyone ever use the bottle-with-brush instead? Then a standard compressed-air can for clean-up? Appears to be more cost-effective, if less convenient.
 
We fixed the 854 power controller. Now the AC power for all of the peripherals is controlled by the key on the processor cabinet.

The 8/e would not boot OS/8 from the RX01 floppy today. It worked OK after we reseated the microcode ROMs in the RX01 diskette drive. To make it more reliable we removed the microcode ROMs, cleaned the tim plated leads, treated them with DeoxIt, and reinstalled them. The RX01 works OK now, and hopefully it stay that way.

The right diskette drive doesn't work correctly. While running diagnostics we compared the INDEX, TRACK 0, and RAW DATA signals from the two drives. As far as I can see they both look the same. The controller was reporting "A Preamble Could Not Be Found" errors. Next week we can swap the two drives to see if the problem is in the analog board or the diskette drive.
 
Only the left diskette drive on the PDP-8/e works so we swapped the left & right diskette drives. If the reading problem is in the drive the problem will follow the drive. If the problem is in the analog board in the RX01 the problem would not follow the drive. The problem followed the drive, so we know the analog board is OK.

We found a diskette drive in the warehouse that had "RX01 ONLY" silk screened on the side, so we tried that one. The replacement drive had a resistor in the read/write head connector and one on another signal connector. The replacement drive didn't work, even after removing the resistor on the head connector.

Now that we know the problem is in the drive, we can compare the signals between the working and broken drive to see if I can isolate the problem and possibly fix the diskette drive.
 
We replaced the left diskette drive in PDP-8/e again today, and actually found another one that works! This one looks like a slightly newer model because it has a resistor in the data head connector. The resistor is only used in RX01 subsystems, so the diskette must also work in the newer RX02 subsystem.

So now both diskette drives are working.

Time to fix the MI8E bootstrap board so the 8/e will boot from diskette with the push of a button.
 
I bought an MI8E bootstrap board from William Donzelli a few months ago. This board contains a 12x34 diode array that is really a ROM containing bootstrap code. The board is manufactured with all diodes installed (0 bits) and diodes are cut out to represent 1 bits. When you toggle the SW switch on the front panel the MI8E board emulates someone flipping the switches on the front panel to toggle in and run a bootstrap loader. The one that I bought contains the RX8E diskette bootstrap.
I installed the MI8E, toggled the SW switch, and was really surprised when OS/8 booted from the floppy. A 40 year old board worked without any repairs!

Now that both floppy disk drives are working it was time to attempt recovering my wife's Masters thesis from 8" floppies. She did all of the thesis documents on a DEC WT-78 word processing system quite a while ago. DEC used two recording formats for 8" floppies on the PDP-8. One was 12-bit based and one was 8-bit based, and both were IBM SSSD format. The PDP-8/e can use either version. The OS/8 installation that I am using defaults to 12-bit mode, but the console command "SET HANDLER FLOP=BYTE" will change the floppy disk device handler to 8-bit mode. Doing a DIR on the WT-78 floppy yielded a "bad directory", which was what I expected with a decades old floppy. Further investigation showed that DEC made a program "WPFLOP" to read/write Word Processing floppies. I used the console command "R WFLOP" to run the program, and "RXB1:1" and hit the Escape key to type file #1 on the console. Word Processing file #1 conveniently was the file directory listing. Using WPFLOP I have recovered 2/3 of the Masters thesis files and have converted it to an MS Word file. I will convert the remaining files tomorrow.
 
Very nice - I think you've more than earned an "easy one"! Even better that you get points with your wife for helping her out!

What is the Y suffix on your board? The printset I have from bitsavers lists variants from YA through YM but nothing for the RX8E.

I am currently using a reconfigured blank board to boot SerialDisk and plan to convert a YE (Typset RIM) to RX8E using information from Lou Ernst. It would be interesting to compare his version with yours.

Jack
 
Sorry for the confusion - from your description, it sounded as if the card was already pre-configured for the RX boot when you got it form Will. I've got a few of the boards here, some OK, some not so OK.

Question for anyone who has played with one of these boards - have you been able to locate the ENABLE flipflop mentioned in the trouble shooting section on page 4-7 of the manual (actually Chapter 4 of Volume 2 of the PDP-8/E Maintenance Manual)? I can't find it on the print and at first figured it was a typo, that the manual was referring to the DATA f/f since it has two enable lines coming out of it but in the next paragraph the DATA f/f is referenced.

Jack
 
Jack, There are no signs of any soldering on the MI8E that I have, either in the diodes or the jumpers, and there are magic-marker dots next to the jumpers that were removed to to set the addresses. I can't tell if this was a generic MI8E that someone configured for the RX01, or if it was done at the factory. I will take some pictures of it and post them on the RICM WWW page.
 
We used David Gesswein's dumprest tools to make new diskettes from images. So far we have bootable OS/8 with diagnostics, OS/8 with Fortran-IV, and COS-310. COS-310 was targeted towards business use, but we haven't found a copy of the DIBOL language to run in it. We are also looking for a copy of the WPS word processing software to run under OS/8. None of the diskettes have support for the DECtape, so we will need to learn how to reconfigure the OS handlers.

The MI8E bootstrap board is very nice. Just toggle the SW switch and it boots from diskette.
 
PDP-8e_WPS-8.jpg
I made a diskette of the WPS word processing software for the PDP-8/e. It booted and ran just fine, and I was able to look at the the files on the diskettes that contained my Wife's master's thesis. I was surprised to see that the contents of the MQ register display on the front panel of the 8/e was cascading lights while it was running. Someone at DEC had too much time on their hands! We have an LQP-02 printer, so I might see if I can get that connected and working with WPS.

WPS normally ran on a dedicated WT78 that was a PDP-8 microprocessor inside of a VT-52 terminal. This was very cool stuff 30 years ago.
 
Mike,

This is great. I always wanted to do this myself. Can you provide some detail as to where you found the disk image? Not all WPS-8 systems were run on VT78 or decmates. There were large systems called WS200 that used an 8/a, supported multiple terminals, and stored files on RL02. I have a pocket service guide for those systems which I need to scan and get to David G. someday.

I have bootable WPS RX02 for my decmates, but never saw a bootable RX01 with WPS. If it's not too much trouble, can you e-mail me or post a link to an imagedisk image of this floppy?

Thanks,
Lou
 
Lou,

I got the ws78_v3.4_wps_system_disk.rx01 image from Dave's WWW page at ws78_v3.4_wps_system_disk.rx01.

I don't have a clock board in my 8/e, so the elapsed time and the date/time on WS78 don't change.

I need to get a VT-52 and LQP-02 connected to the 8/e so my wife can have flashbacks to working on a new WP-78.

Seeing your WS200 service guide would be interesting.
 
m_thompson said:
Where can I get some RX01 SSSD 8" floppies to go with this system?
Used are OK.
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I might have some. I have two hard cases (one plastic, one cardboard) full. But they may not be SSSD.
I'd have to look. You are likely to find someone closer that may have them too. I'll take a look at what
mine are.
 
Hi All;
For those of Us, Like me not in the know..
Are these Hard Sector OR Soft Sector, ecxept for needing to be Formatted, would any 8" work as long as it was the same type, Hard vs Soft Sector ??

THANK YOU Marty
 
Marty said:
Hi All;
For those of Us, Like me not in the know..
Are these Hard Sector OR Soft Sector, ecxept for needing to be Formatted, would any 8" work as long as it was the same type, Hard vs Soft Sector ??

THANK YOU Marty
Click to expand...
RX01 is soft sectored. This is hard sectored:

Hard%20sector%20diskette%20for%20Incoterm.png


Used on the Incoterm SPD 10/20. They still need to formatted but the start of a sector is indicated by a hole in the diskette. I think that a hard sectored disk would work fine in a soft sector drive.
 
Hi All;
MattisLind, "" I think that a hard sectored disk would work fine in a soft sector drive. "" NOT Usually.. Now my experience is with Shurgart 8" Drives, But, I would say NO !! I know the Difference, I have Hard Sector for my Altair 8800 and I have Soft Sector for when I am running with John's Z-80 and ZFDC Board.. A hard Sectored Diskette has tooo many holes for a soft Sectored system..
And the one You are showing has the Sector Holes in the Wrong place, from what I have.. So maybe RX01 has its sector hole different than mine..

1148.jpg 1149.jpg 1151.jpg

THANK YOU Marty
 
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Marty,

The hard sectored disks for your system look a lot like an RX01. The sector hole is in the usual place (near the hub), but there is one hole for each sector. Long long ago you might remember the 2 and change boxes of Memorex hard sectored floppies I sent you. The reason the third box was partially full was because way back, out of desparation, I opened the jacket on one of those floppies, took the media out of the jacket, and cut a ring of tape to block all but one sector hole. That basically turned the hard sectored disk back into a soft sectored disk. I did format it as a real dec RX01 in my DSD440. I still have that disk (but didn't use it much as I was luck enough to find a guy nearby with some soft sectored disks.

Lou
 
Hi All;
Yes, Lou, I remember.. I guess that would be approach, "" and cut a ring of tape to block all but one sector hole. ""
And with my Pictures, I was trying to show the difference between the two..

THANK YOU Marty
 
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