PEB Problems (Disk Controller, RS232)

[h0trod]

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

Edited February 1, 2023 by h0trod

[Stuart]

Basic (excuse the pun!) check of the disk controller card DSR using a TI Extended BASIC cartridge: http://www.stuartconner.me.uk/ti/ti.htm#checking_disk_controller_card_dsr

 

This post ... 

... suggests that a null modem cable might be needed. Take a look at that thread and see if it helps.

Edited February 1, 2023 by Stuart

[h0trod]

15 minutes ago, Stuart said:

Basic (excuse the pun!) check of the disk controller card DSR using a TI Extended BASIC cartridge: http://www.stuartconner.me.uk/ti/ti.htm#checking_disk_controller_card_dsr

 

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?

[+dhe]

32 minutes ago, h0trod said:

Does XB try to do something with disk on start?

Yes. A regular (stock) TI XB cart will try to load a file called DSK1.LOAD when you choose XB from the main menu.

 

Having another disk controller and interface card would be key to figuring out where you problem is. What seems to be a disk controller problem, can easily be caused by a flacky interface card.

 

As I discovered in another thread, the interface card, can be a bugger, because what you think might be a flacky or bad chip, can be a dodgy connection on either end of the fire house.

 

 

[h0trod]

1 minute ago, dhe said:

Yes. A regular (stock) TI XB cart will try to load a file called DSK1.LOAD when you choose XB from the main menu.

 

Having another disk controller and interface card would be key to figuring out where you problem is. What seems to be a disk controller problem, can easily be caused by a flacky interface card.

 

As I discovered in another thread, the interface card, can be a bugger, because what you think might be a flacky or bad chip, can be a dodgy connection on either end of the fire house.

 

 

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

[+dhe]

I'm not a hardware guru - there are folks here who are.

 

But, testing the memory will exercise some of the data/address lines, working with the disk controller will use CRU lines and other control signals that just memory will not.

 

If you had a sidecar TIPI, then you could test the cru lines, leaving out the pbox. It's also possible, the 9901 in your console has a problem, and it's not pbox related at all.

 

Do you have another console to try?

[WhataKowinkydink]

3 hours ago, h0trod said:

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.

It's been a spot since I've done some serial operations but I recall using a null modem cable.   PuTTY + TE II should at least give you some basic ability to test things.   Once you get your disk drive sorted out you can get TELCO (a much better terminal emulator) and then do some more serious serial ops.

[+arcadeshopper]

A TI Modem connection needs to be 2-3 3-2 7-7 and probably 6-20 but ymmv.. (null modem)  this is because the modem and the TI are the same DCE/DTE format.. while a PEECEE is the other.. so modems plug in with a straight cable.. interestingly, a pc plugs in with a straight cable to the TI for file xfers

 

I sell an adapter in my store for your modem to work if you need

 

Greg 

[Stuart]

11 hours ago, h0trod said:

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?

Yes, XB tries to load the file DSK1.LOAD as dhe stated. Try powering on just the console first, select XB, then power on the PEB, then try the first two lines of that BASIC program and see if they run or give an error. If they do run, then try the rest of the program. If they give an error (because XB didn't find the 32K RAM at startup) ... anyone know if XB can be convinced that the 32K is there after startup?

 

Plan B: If you have, or where planning to get, one of the 64K/128K cartridge boards, then I have an EPROM image for that (http://www.stuartconner.me.uk/ti/ti.htm#minimem_lbla_tibug_disassembler_cartridge) that includes TIBUG, which will let you test the card in the same way as the MiniMem EASYBUG.

[h0trod]

4 hours ago, Stuart said:

Yes, XB tries to load the file DSK1.LOAD as dhe stated. Try powering on just the console first, select XB, then power on the PEB, then try the first two lines of that BASIC program and see if they run or give an error. If they do run, then try the rest of the program. If they give an error (because XB didn't find the 32K RAM at startup) ... anyone know if XB can be convinced that the 32K is there after startup?

 

Plan B: If you have, or where planning to get, one of the 64K/128K cartridge boards, then I have an EPROM image for that (http://www.stuartconner.me.uk/ti/ti.htm#minimem_lbla_tibug_disassembler_cartridge) that includes TIBUG, which will let you test the card in the same way as the MiniMem EASYBUG.

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!

[h0trod]

13 hours ago, arcadeshopper said:

A TI Modem connection needs to be 2-3 3-2 7-7 and probably 6-20 but ymmv.. (null modem)  this is because the modem and the TI are the same DCE/DTE format.. while a PEECEE is the other.. so modems plug in with a straight cable.. interestingly, a pc plugs in with a straight cable to the TI for file xfers

 

I sell an adapter in my store for your modem to work if you need

 

Greg 

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.

[Stuart]

2 hours ago, h0trod said:

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.

So that indicates that your PEB interface is working OK. You might want to try replacing the 74LS245 near the PEB edge connector on the disk controller card ... that's often the culprit.

[h0trod]

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.

Edited February 3, 2023 by h0trod

[h0trod]

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.  

[Stuart]

The TMS9902 RS-232 interface chips plus enabling/disabling the card all use the CRU interface, so that must be working for you to have got as far as you have.

[h0trod]

On 2/3/2023 at 1:40 PM, h0trod said:

Disk Controller: Got a 74LS245 on the way, fingers crossed.

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

[h0trod]

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.

Edited February 9, 2023 by h0trod

[Stuart]

1 hour ago, h0trod said:

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.

Does the controller card LED come on when you run the program, out of interest?

[h0trod]

Just now, Stuart said:

Does the controller card LED come on when you run the program, out of interest?

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

[h0trod]

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.

[+dhe]

@Shift838 made or makes a PBOX interface card.

 

It's great because it's three parts. Console Interface side, cable and PBOX interface side.

 

If you can get one of those it would make trouble shooting easier, because a bad flex cable can exhibit a lot of different symptoms and is really the weak link.

 

And even worse, since the connection can be weak / not connected / working from one test run to the other, you can end up chasing a lot of ghost - not like a chip that simply doesn't work.

[WhataKowinkydink]

4 hours ago, h0trod said:

it doesn't even flash briefly at power on.

Which it definitely should do - good catch.  @dhe has a good point too about the flex cable. 

[h0trod]

35 minutes ago, WhataKowinkydink said:

Which it definitely should do - good catch.  @dhe has a good point too about the flex cable. 

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.  

[h0trod]

9 hours ago, h0trod said:

 

I was able to run the XB test program and it returned alternating rows of

0 0 0 0 0 0 0 0

. . . . . . . . 

 

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.

[Stuart]

On 2/9/2023 at 8:37 PM, h0trod said:

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.

Try replacing U6 on the Disk Controller as well, which is a 74LS125. With that replaced, you've replaced pretty much all the ICs that interface the card with the PEB bus. If the Disk Controller still interferes with the RS-232 card, remove the 74LS125 and 74LS245 and try the RS-232 again. This leaves just the 74LS244s which are inputs from the bus so they shouldn't affect the operation of the RS-232. If the RS-232 still doesn't work, remove the 74LS244s as well in case one of them is duff and try again. If still no joy, take a close look at the replacements you've done and see if you've damaged or bridged a track.