[TUHS] Re: AT&T UNIX PC (7300) Teardown and Restoration

[segaloco via TUHS <tuhs@tuhs.org>]

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Nope, unfortunately I only know as much as is needed to plug into the GPIO RX/TX/GND working on single boards. I wouldn't be surprised if my assumption I just run these pins into the D-25 in the right holes is bunk...but that's how we learn sometimes. Once I move I should be able to setup a proper work bench where I can tinker on this sort of thing more intentionally rather than haphazardly. So perhaps a silly question for an expert but a valid one for me. I'll chase that angle and see if it bears fruit.

- Matt G.
------- Original Message -------
On Tuesday, January 3rd, 2023 at 4:40 PM, Warner Losh <imp@bsdimp.com> wrote:

> On Tue, Jan 3, 2023, 5:30 PM segaloco via TUHS <tuhs@tuhs.org> wrote:
>
>> I'd love to get my hands on a 3B2 someday, this'll be cool if I can get it going but that'd be a much more robust machine.
>>
>> I'm starting to suspect if there isn't any sort of boot ROM that spits out commentary on the UART and that doesn't get flexed until UNIX is up, I may not be able to get very far. I referred to http://bitsavers.trailing-edge.com/pdf/att/3b1/999-809-010IS_UNIX_PC_Remote_Access_1986.pdf for the serial settings and it appears:
>>
>> 9600 baud, 1 stop bit, no parity, 8 data bits
>>
>> And the relevant pins
>>
>> Pin 1 - GND
>> Pin 2 - RX
>> Pin 3 - TX
>> Pin 4 - RTS
>> Pin 5 - CTS
>> Pin 6 - DSR
>> Pin 7 - GND
>> Pin 8 - DCD
>> Pin 20 - DTR
>>
>> So I've plugged my USB-TTY GND/RX/TX into the relevant pins and setup the necessary tty settings. The manual then suggests if running null modem mode to short pin 4 to 5 and then pins 6, 8, and 20 together, presumably omitting any need for modem signalling from the remote machine, doing basic serial RX/TX. Unfortunately even with all of this bypassing I get nothing out of the RS-232 port. What I don't know is if I could even expect something or if this is unlikely to bear fruit whether the hardware works or not. In any case, if I do get this thing running I'll have a writeup for folks afterwards. If not, then hopefully I can figure out something useful to do with this thing rather than junking it.
>
> Silly question... did you level shift to RS 232 levels? You likely did... but if not...
>
> Warner
>
>> - Matt G.
>> ------- Original Message -------
>> On Tuesday, January 3rd, 2023 at 3:53 PM, rob@atvetsystems.com <rob@atvetsystems.com> wrote:
>>
>>> Hello Matt,
>>>
>>> I’ve got one of these in my garage. I bought it about twenty years ago as a working system but when I got it home I noticed that the hard disk wasn’t connected but at some point I’d like to get it and my 3b2/300 working.
>>>
>>> Regards, Rob.
>>>
>>>> On 3 Jan 2023, at 23:27, segaloco via TUHS <tuhs@tuhs.org> wrote:
>>>>
>>>> And here are some pictures of the guts.
>>>>
>>>> https://imgur.com/a/E1ioxZl
>>>>
>>>> Various bits inside date this to late 1985. The good news is it at least turns on, but that's about as far as I've gotten with it. The display never turns on, nor do I hear any sounds indicating it tries to start the CRT. The fans kick on and there it stays until I turn it off. I plugged in a USB-TTY to pins 2, 3, and 7 (RX/TX/GND) and listened at 9600 baud 8 bit 1 stop no parity and got nothing. Swapped the RX/TX, still nothing. Of course, that's all predicated on the assumption there's something there to even interact with. I have little faith that whatever UNIX install was on this is extant. Additionally, it didn't come with a keyboard, so if there was some futzing with key combos that would trigger some sort of UART over those lines, I can't do that. I wonder if there are some contacts inside I can just poll for activity with this serial connector, not sure how safe that is...
>>>>
>>>> Anywho, the CPU has a bit of corrosion on the surface, not sure how that bodes for the innards, but this is in kinda rough shape either way. I hope I can salvage it but if not, I'm going to at least do some study on the CRT particulars and see if I can extract and keep the monitor from it, been wanting a smaller CRT to have around for a while.
>>>>
>>>> - Matt G.
>>>> ------- Original Message -------
>>>> On Tuesday, January 3rd, 2023 at 12:20 PM, segaloco via TUHS <tuhs@tuhs.org> wrote:
>>>>
>>>>> Good day everyone, just starting a thread for yet another project I'll be tinkering on over time. Picked up a (presumably broken/untested) 7300 off eBay to at the very least tear down and get some good pictures of and, with some luck, perhaps get working again.
>>>>>
>>>>> https://imgur.com/a/CExzebl
>>>>>
>>>>> Here are some pictures of the exterior for starters. I'll update this thread when I've got pictures of the guts and also with any info I can glean regarding whether this might be salvageable. The rust on the back is pretty nasty but I've seen older/worse start up just fine.
>>>>>
>>>>> - Matt G.

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