h0trod

There was one easy thing left to try. The FD1771 Floppy Drive Controller IC's are socketed. so I swapped the one from my good controller into my bad controller. No luck. I feel like I'm about to learn a lot more about floppy drive control signals, and get a crash course on how to use this digital oscilloscope..

I spoke too soon. While the "repaired" disk controller seems to load programs OK from the drive, it does not save them properly. I generally get an I/O Error 66 after a save attempt. At this point, the Disk Controller LED remains lit. If I catalog the disk in DM II after one of these failed saves, I see a "program" with no name and a garbage "size" value. DM II disk tests, initialization, disk name all work fine. If I switch to my other working controller, I can save without issue. Beyond frustrated 😡

After replacing the DSR ROMs.. it lives! Thanks a bunch to everyone in the thread for helping me work through the possible issues. It's very satisfying to see it work!

Found some more dodgy solder joints and touched them up, and unfortunately I'm right back where I started. LED flashes at bootup. Stays lit and system hangs upon attempt to access the card (DM II startup screen or Extended Basic startup.) I have a set of DSR EPROMs I may as well try to install before I give up.

Quick update, maybe getting somewhere. I replaced both the 74LS245 (again, and socketed it this time) and the the 74LS125. Still had the issue with the TI locking up at boot when the RS232 card is in. Removed all 74LS244s, RS232 behaves correctly. Trying one 74LS244 at a time, determined issue only occurs when a chip is installed in the center socket. Swapped around chips to verify it is indeed the socket not the chip. Found a short between two pins with the multimeter that I could barely see even with magnification. Good news: after fixing this, I no longer have issues with the card interfering with RS232. Bad news: still no sign of life from the card: not even the brief flash at power on. DM II gives me Disk Error 0. Will continue taking a close look at my solder job, and I have at least one spare for each of these chips and I will try some swaps. Will also try again to read ROMs. I may also replace the 5V regulator, despite it reading a solid 5V it gets very hot and has long since separated from the thermal paste that once upon a time sunk the heat, but I doubt this is the primary issue.

An interesting thought, worth trying! And I did. I still get all zeros. I'm assuming the upper ROM starts at 0x5000 (20480 decimal). Since I don't think the card is being enabled, I'm not surprised by this result, but I appreciate the idea. I can almost type this XB program in from memory now 😂

Yes, with the working card the test program works exactly as expected.

Maybe I'm misunderstanding - but I think it must, or the program would be pointless, no? The program is linked earlier in the thread. FWIW, I got another disk controller card to try and it's working fine - so I suspect my problems are confined to the controller itself and not the PEB, firehose, etc. Still planning on doing my best to get the original card running, waiting on some parts.

I have some ROMs on the way just in case. But the output from the XB test program that's supposed to read the beginning of the ROM contents has me believing that I'm not successfully reading the ROM, not that it's corrupted.

Thank you. I appreciate your continued assistance! I have checked under magnification and tested adjacent pins for shorts and am fairly sure nothing is bridged. I have also begun checking every trace from the 245 and 244's to their destinations for continuity to be sure I didn't lose a pad or a trace in my soldering / desoldering efforts - that's still ongoing but so far I have found nothing. It's still possible I applied too much heat and damaged something downstream. I will try your suggestions.. I wish I had a local source for these parts!

I have also confirmed that this is the same output I get when the card isn't even installed in the PEB. Not surprised, since when it is installed it's not "turned on" according to the LED.

Yeah, I almost wonder if I made things worse with the chip replacements. The LED did flash at power on previously. We'll see what happens when I get the other Disk Controller card in. This isn't a project I want to throw too much money at. But I certainly want it working, and if I become convinced that the flex cable is the most likely issue, I'll pursue it.

There are additional issues when the Disk Controller and RS-232 card are installed together. The RS-232 card works fine when the Disk Controller is not installed (to the extent I've already documented here.) But if both are in the PEB at the same time I get strange behavior. On my first attempt, I launched TE II and after going through the configuration screen, the TI immediately rebooted to the title screen. After shutting down and trying again, the TI won't boot to the title screen with both cards in, and the RS-232 led remains lit. If I take the Disk Controller back out, RS-232 worls fine again.

No LED while running. Also happened to notice - it doesn't even flash briefly at power on.

Progress, maybe. I replaced the three 74LS244s on the controller card, and attempted disk accesses no longer lock up the system. Any attempt to use Disk Manager to access the drive returns an instant "Disk Error 0". I was able to run the XB test program and it returned alternating rows of 0 0 0 0 0 0 0 0 . . . . . . . . So clearly I still have issues. I have another Disk Controller card on the way so I can compare behavior.

The part arrived today, unfortunately the swap had no effect. Barring other suggestions, I will try replacing the 244's next.

I have scanned and uploaded the Myarc RS-232 manual to the Internet Archive. I'm not a frequent scanner, so please forgive the imperfections. https://archive.org/details/myarc-rs-232-interface-card-rsic-1

Sorry for responding to myself here, but I hacked together the simplest possible null modem: 2-3, 3-2, 7-7 and finally got something to work. Clearly there's something going on with the handshaking lines that I don't understand and is going to take some more digging. The Myarc manual says Pin 5 (CTS) function is "Clear to send CRU out". That has me a little nervous, since one of the comments about the disk controller issues was "might be CRU related", and now I see that "CRU" again next to something possibly related to this dodgy handshaking.

RS232: Got a loopback dongle and a null modem adapter in the mail today. Loopback adapter, no issues. Characters sent in full duplex mode are echoed back to the screen. With high hopes, tried null modem adapter to WiModem232.. nope. Try to send a character and LED on card lights and stays lit, no action on screen. Disconnect WiModem, light goes out. My guess is something is going on with control signals (CTS, DSR, DCD, DTR). I am trying to make sense of these pages in the WiModem manual, and determine whether they might apply to the Myarc card. My WiModem is the v1. Disk Controller: Got a 74LS245 on the way, fingers crossed.

Some success on the RS232 front. With the O-scope I was able to see bytes were being sent on pin 3, so I knew the card was not completely dead. The comment above and a consult with the Myarc manual gave me an idea of what I could try now, before my null modem adapter arrives: I should be able to connect the TI directly to my DEC VT131 terminal with the straight-through cable I have. It worked! One down, one to go.

On my to-do list for the weekend.

Plan A: I get the error. XB doesn't know about the 32K when started up this way. Plan B: I don't have any special carts or anything yet, but making a list of things that will be useful in investigating this. Thanks!

I thought that a successful test of the 32K card would (likely) rule out the interface card. Not true?

Thanks - I guess I had thusfar neglected to actually try starting Extended Basic with the Disk Controller card in the system, because it seems that locks up the system in the same way! Does XB try to do something with disk on start?

I got my first TI around age 10.. and my first PEB a few days ago at age 46. I'm trying to test everything bit by bit, but the PEB stuff is all new to me. It included four cards: Flex Cable Interface, 32K Memory, Disk Controller, and Myarc RS-232. The TI disk drive is also in the PEB. I think the Flex Cable and 32K are fine. Extended Basic was able to see the 32K (with "SIZE"), and I was able to type in and run one of the 32K test programs in this thread, which report all chips good. I don't know how exhaustive such a test is, but it's a start. I tried to use the Myarc card connected to my WiModem232 with no joy. I connected the WiModem to a separate terminal and configured it for 300 baud, 7E1. I then connected it to the Myarc card (with a DB25 M-M gender changer) and configured Terminal Emulator II with these parameters. I just get the cursor in the top left, and nothing I type is echoed. I believe this configuration should work (ie, I don't think a null modem cable should be required), but I am waiting on a loopback connector to definitively show if it's working or not. I tried the card in multiple slots (also with the flex cable in multiple slots), and with all the other PEB cards except the Flex Cable removed. I also tried with the other end connected through the Speech Synth pass-through port as well as directly to the TI. No dice. That brings me to the Disk Controller. Every time the PEB tries to access the Disk Controller, the TI locks up and the LED stays lit. I found this thread which mirrors my symptoms exactly, but it doesn't look like the OP was able to track down the root cause. Like the OP in that thread, the lockup occurs whether or not the Disk Controller is connected to the drive. I tried all the slot-moving tricks with this card, as well. As a first step I checked the output voltages and the 5V and 12V regulators on the card and they are spot on. I examined the rear for cracked solder joints or rework. No obvious bad joints, but it looks like there was a little rework around the one custom chip towards the left of the board (opposite the connector side). The thread mentioned above talks about some debugging steps using the Mini Memory cart, which I don't have. Wondering if there's any way I can use XB to probe at the card, or perhaps attempt to read the ROMs? Any other ideas? I'm OK with a multimeter and oscilloscope but no experience troubleshooting digital logic. Thanks J