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DEC Rainbow PC100A - Replacing bad RX50 with dual Gotek drives, strange behavior...

T

Thatsmanjear

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I had a dusty Rainbow PC100A not being used because the RX50 floppy was bad (both A: and B: ) and I could never figure out how to get them repaired...I tried! So decided to just swap them out for a pair of Gotek floppy emulators. Using the metallic shell that originally surrounded the RX50 and the sled, I 3D printed some Gotek drive trays, drilled a few holes, mounted them up and have a perfect dual-Gotek "module" that is easily installed and removed as needed. ANYWAY...the reason for this post is because the dual Gotek setup causes a strange POST error if I don't have TWO USB drives installed in the two Gotek's during POST.

Drive A: Gotek has jumper S0
Drive B: Gotek had jumper S1
34-pin floppy cable is straight, no twist, two connectors for the two Gotek's.
FF.CFG on the USB drive for the Gotek has: interface=shugart and host=dec

If I just wire up one of the Goteks by itself, then POST is fine, booting is fine (if the Gotek is the A: (S0), or B: (S1) then selecting the appropriate option at the boot screen works)

If I wire up BOTH Goteks at the same time, but only one of the Goteks has the USB drive plugged in, then the POST fails with LED pattern (2-3-7), which is "Remove card or check diskette".

If I wire up BOTH Goteks at the same time, and have two USB drives plugged in, then it will POST and boot fine (either A: or B: ).

If I wire up BOTH Goteks at the same time, have two USB drives, POST and Boot, then I can remove one of the USB drives (e.g., boot from A: and remove the B: USB drive) and it continues to work fine. Obviously if I try to access B: then I get a drive not found error, but I can then plug the Gotek back in and it works, just like removing and inserting floppies.

What confuses is me is that obviously I don't need to have two real floppies inside an RX50 to boot the Rainbow off of a single drive.

During POST, it hits Drive A: then hit Drive B: (the activity light on the Gotek lights up momentarily).

Any ideas?

20260429_151041.jpg 20260429_172453.jpg 20260429_172434.jpg
 
While the symptoms were not exactly the same here, I've experienced a lot of silliness when trying to use a pair of Gotek drives on a Pro350. I was never able to nail it down completely but there is some logic buried in the firmware that expects RX50 behavioral quirks. If you are in an experimental mood, try flashing both Gotek units with this test firmware. It contains a small update that ensures both drives step in unison as would a real RX50. I'll be very curious to see if it helps.
 

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Hi, thanks for the response. I flashed both Gotek drives with your firmware and the behavior was the same, it won't POST cleanly unless both Gotek's have a USB drive inserted.

I agree that the way the RX50 uses common spindle and stepper motors it's like when the firmware code is checking Drive A: it must be expecting Drive B: to be returning some status as well, and the Gotek obviously doesn't respond like it wants.

While a solution would be nice, it's not terrible to have to insert another USB drive into B: during POST then just remove it for the rest of the session.
 
Well, it was worth a try. I developed that patch when working with a DECmate III. There, it did solve a bunch of issues. It expected both A and B to report track 0 when only one was actually homed.
 
Now, just to confuse things, I finished putting a dual Gotek in a DECmate II to replace the RX50 there and it works perfectly. The same Gotek pack in my Pro 380 gets sadface from the diagnostics.

Note that I *did* use a twisted cable for the DECmate. I jumpered the top one (after the twist) to MO. The bottom was left with default settings (old LED one, I think S0). Both drives work independently and I can boot it up with neither having a USB drive in, but I also suspect the DECmate II is less finicky about this. Settings in FF.CFG were

interface = shugart
host = dec
pin02 = low
pin34 = rdy
 

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  • PXL_20260422_213632395.jpg
    PXL_20260422_213632395.jpg
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ClassicHasClass said:
Now, just to confuse things, I finished putting a dual Gotek in a DECmate II to replace the RX50 there and it works perfectly. The same Gotek pack in my Pro 380 gets sadface from the diagnostics.

Note that I *did* use a twisted cable for the DECmate. I jumpered the top one (after the twist) to MO. The bottom was left with default settings (old LED one, I think S0). Both drives work independently and I can boot it up with neither having a USB drive in, but I also suspect the DECmate II is less finicky about this. Settings in FF.CFG were

interface = shugart
host = dec
pin02 = low
pin34 = rdy
Click to expand...
You may want to beat on the diskette subsystem before declaring victory. I had what appeared to be initial success with unmodified Flashfloppy firmware on my DECmate III, but after trying a round of format/copy and diagnostics it started throwing errors. These were only mitigated after I patched the firmware to make both drives seek in unison when only one was selected.
 
Thatsmanjear said:
Hi, thanks for the response. I flashed both Gotek drives with your firmware and the behavior was the same, it won't POST cleanly unless both Gotek's have a USB drive inserted.

I agree that the way the RX50 uses common spindle and stepper motors it's like when the firmware code is checking Drive A: it must be expecting Drive B: to be returning some status as well, and the Gotek obviously doesn't respond like it wants.

While a solution would be nice, it's not terrible to have to insert another USB drive into B: during POST then just remove it for the rest of the session.
Click to expand...

Just for kicks, what happens if you swap the Goteks around without changing those jumpers? Does anything change?

If you have a flash drive in the first Gotek and not the second does swapping them around make any difference?

Basically the questions are:
- Does it only boot from the first drive?
- Does it know which drive is which?
- Does it just check both for a valid boot disk anyway?
- Do the Gotek units actually check these S0 and S1 jumpers and respect them?

P.S.

I know that in PCs from a particular era onward, the drives are internally wired/jumpered to be the same and so the twist in the cable dictates which actually sees the active drive select.
 
ClassicHasClass said:
How odd. Maybe the DECmate III is more persnickety about that than the DECmate II?

I'm tempted to try your firmware to see if that makes my Pro 380 happy, or have you already?
Click to expand...
As luck may have it, although the software change was developed with my Pro 350 in mind I have not had a proper time slice for testing on that machine. The fact that it corrected the DECmate III problems was icing on the cake.
 
Istarian said:
Just for kicks, what happens if you swap the Goteks around without changing those jumpers? Does anything change?

If you have a flash drive in the first Gotek and not the second does swapping them around make any difference?

Basically the questions are:
- Does it only boot from the first drive?
- Does it know which drive is which?
- Does it just check both for a valid boot disk anyway?
- Do the Gotek units actually check these S0 and S1 jumpers and respect them?

P.S.

I know that in PCs from a particular era onward, the drives are internally wired/jumpered to be the same and so the twist in the cable dictates which actually sees the active drive select.
Click to expand...
Hi, yes, the Gotek's honor their S0/S1 jumper setting. I can choose to boot from A: from the Rainbow boot menu and it boots off the Gotek jumpered to S0. Or I can choose B: and the Gotek jumpered to S1 is the boot device. (both of those cases are with a USB flash in each). I didn't try having a USB flash in only drive B:

...and in the meantime I thought I'd try to fix my VR241 monitor because the top row of characters is about 3/4 cut off and no about of fiddling with the adjustment pots on the monitor CRT board could correct it. Figured I had some grumpy capacitors, so in the process of probing/replacing caps.
 
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