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Can I run an RL02 on a PDP-8/M???

Well, it's been five years since I fired up the 8a and RL02... had to dig everything out of the heap in the garage and cable the DEC Writer II back to the system (I had used it for the 8m back then). OS/8 booted no sweat, so it looks like all the hardware still works fine. I took a look inside the card cage and noted that some of the slots at the bottom are only quad wide, versus hex, and the RL8A is plugged in to one of those; so that pretty clearly confirms the other two card 'tabs' are unused!

Tomorrow I'll try to get the RL8A plugged into a slot on my 8m.

So, two questions:
1) What are the odds that the OS/8 build for my 8a will boot "as is" on my 8m?
2) Is there a simple bootstrap that I can toggle into my 8m to boot OS/8?
(The 8a is too simple: it has a 'boot' key on the front panel:D)
 
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Perfect!
I spent a little time trying to find that info with no luck; from your post it appears you did too!
I was starting to think I was going to have to find the bootstrap code in my 8a, but you did the work already:)

Unfortunately, I only have 8K in my 8m... we'll see how it goes. I always assumed I was going to need 12K to run TSS8 anyway, but I've found a little contradictory info in some early TSS8 docs that imply that a 4 user system could run with only 8K; I'm skeptical since the Monitor takes two fields and I thought it was always resident (FIP and SI are swapped as needed). But, maybe TS8II (field 1) can be swapped, as well?

Lou - N2MIY said:
I posted the RL8A bootstrap in this thread: http://www.vintage-computer.com/vcforum/archive/index.php/t-35640.html

Your RL8A OS/8 pack should boot on the 8/m. Does the 8/m at least 12kW of memory? The RL handler is a two-page handler.

Lou
Click to expand...
 
AteEm said:
Unfortunately, I only have 8K in my 8m... we'll see how it goes. I always assumed I was going to need 12K to run TSS8 anyway, but I've found a little contradictory info in some early TSS8 docs that imply that a 4 user system could run with only 8K; I'm skeptical since the Monitor takes two fields and I thought it was always resident (FIP and SI are swapped as needed). But, maybe TS8II (field 1) can be swapped, as well?
Click to expand...
From what I remember (which may not be accurate as my memory fails me at times) I think TSS/8 needed a minimum of 12k. You are right FIP and SI would swap in when needed. Your user space would also swap in too. Of course another 4k or 8k would make the system perform much better. I wanted to see it run again on an 8i as it's front panel is so much nicer than the 8i as it displays all the info all the time as opposed to the rotary switch on the 8e where you could choose what to view on the lights. TSS/8 ran the null job which would just make the lights count in the AC. We used to try to write programs to make the AC do other things. Rotate a bit left to right, right to left, count down, etc. Yeah, we were bored and just wanted to see what we could do. :)
 
OP here with an update after the holidays slowed things down:p

Pulled the 8m out of storage with the intention of plugging in the RL8A...I figured to just get the system up and running in its old configuration and make sure I could run a couple diagnostics first. Turned the system on and started to toggle in a quick test program...maybe two or three minutes later all the front panel lights go out along with the fans all slowing WAY down...two seconds later the circuit breaker on the back pops:-(

Power supply bridge rectifier toast. So, I manage to find a replacement and buy two. Put one in and fire it up...a few seconds later and I see a spark and smoke from the where the power cord enters the chassis; there's a little box containing the various power supply connectors and XY caps/transorbs. Turns out that all of my plugging and unplugging of the connectors had caused the connector that was soldered to the board inside the little box to break loose. That turned out to be quite a little repair job since the smoke and flash had come from what was left of the PCB trace vaporizing!

After getting it all back together, I decided to check the bridge rectifier and found it was damaged! So, like a TOTAL MORON, I ASS-U-MEd that it had been damaged by the failure I'd just had. If I'd stopped to actually think about it I would have realized that couldn't have caused the bridge rectifier to fail...the trace blowing open was really just acting like a fuse.

So, I proceeded to put in my backup bridge rectifier and, what a surprise, blew it up as soon as I turned the power on!! Have I mentioned how STUPID I am??

Finally, entering proper troubleshooting mode I decided to actually look into why the bridge blew up the first time! Turns out one of the two 24,000 uF caps in the power supply is a dead short.

In looking at the circuit, I'm a bit curious about the design of the front end. It's a pretty classic full-wave bridge out of a CT transformer, but the bridge directly feeds the two 24,000 uF caps which, judging from their physical size, are low ESR. That implies the potential for a huge inrush current when first applying power. I'm somewhat concerned if I purchased a replacement bridge with a sufficiently high current rating (25 Amp), since I couldn't find and data on the OEM part. My replacement bridge is physically larger, but that may not mean much. All I can assume is that DEC designed enough impedance into the secondary windings of the transformer to limit the inrush current to a safe value. Anyone know what the current rating of the OEM bridge rectifier in the PSU was?

Anyway, while my local parts store was more than happy to sell me my THIRD bridge rectifier, they said, "Good luck finding the cap!" After some serious online searching I found the 24,000 uF caps of the correct voltage and physical size; not cheap at $17 each plus shipping, but they're on their way (I bought two figuring the other one may be close to failing, too).

Hopefully, they'll arrive by next week and I'll be back to where I was 5 years ago!:p
 
Unfortunately, this is a pretty typical scenario. You might want to wait for Lou to post a reply - he may be able to recommend a few other specifics to check before risking your third bridge.

BTW - please share the source for your parts when you've received them and judged them to be useful.
 
RSX11M+ said:
Unfortunately, this is a pretty typical scenario. You might want to wait for Lou to post a reply - he may be able to recommend a few other specifics to check before risking your third bridge.

BTW - please share the source for your parts when you've received them and judged them to be useful.
Click to expand...

The power supply capacitors arrived today while I was at work and I'm happy to report that after installing them and the THIRD bridge rectifier all voltages came right up! I plugged all the boards back in the OMNIBUS and low and behold I'm back up an running:D Passed the simple AC counting test...probably should run some of the MAINDEC diagnostics, but I'm itching to plug in the RL8A.

Anyway, the bridge was easy to find at a local parts store: NTE5326 (600V, 25A full wave bridge) overkill, but it's what they had in stock.
The capacitor was the tough one to find. The usual distys, Newark, Digi-Key, Mouser, etc. either didn't show an equivalent, or wanted an absurd (like 30 piece) minimum at like $50 each!!
The required caps are 25,000 uF at 50V and need to be 2" dia. x 5 5/8" long. I found them at TEDSS.com for $17.97 each. Their part number is 101-1066-02, phone number is 843-266-0003.
Note that I have the H740 Switcher power supply, NOT the H724 linear used in the 8E.
 
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