Need some help troubleshooting. (UNIX PC, 7300)

[CRD]

Heyo, No idea if this group is still active, but I'll give it a shot considering I have run out of ideas.

I have a 7300 in my possession, it powers up with fans spinning and I can hear the harddrive being accessed but the CRT lights up to a solid green screen. And I have already reseated all my socketed chips, including the CPU, and traced my connections looking for broken traces, vias and bodge wires and found none.

The computer did have loading bars when I originally acquired it, but has since refused to do anything but give a solid green screen.

My question is: What are my options at this point? And is there any fix for this that I haven't tried yet?

Any and all ideas are welcome, I'm at the end of my rope with it as of now.

Thanks, CRD.

[pe...@transcend.aero]

Do you have a bootable floppy disk?

[CRD]

The floppy drive seems to function, but I don't have any floppies.

[Peter Schmidt]

On Friday, December 27, 2019 at 7:36:05 PM UTC-5, CRD wrote:
> The floppy drive seems to function, but I don't have any floppies.

So when you say "solid green screen", is it truly solid, or is it a bunch of horizontal lines with some small gaps?

I just powered mine up for the first time in several years, and that's what it did. :-/ However, I let it sit for 30 minutes, and then power cycled it, and it came up fine. :-)

So, before we get out oscilloscopes to find out what parts in the power supply on on the moboard are marginal, you might try letting it warm up like I just did.

You are also going to need the admin boot floppy to facilitate trouble-shooting, and so you can park the hard disk's heads before moving the machine. Early MFM drives did not auto-park on power off, and I destroyed the first drive in this machine forgetting that, d'oh.

[CRD]

Thank you for the input.

It is truly solid. Photo here:

https://i.redd.it/0i62yx3dhl841.jpg
-OR-
https://www.reddit.com/user/RetroProcessor18/comments/eji8hx/att_unix_pc_7300_power_up/

I will double check and let the computer run for a time.

I am also concerned as when I acquired the computer it at least started running the loading bars, the hard drive spins up, but I do not know if it is damaged. I do have an adapter board to replace the hard drive in the future.

[pe...@transcend.aero]

This may not be the root cause of the green screen, but the 3B1/7300 will overheat after some smallish number of minutes running with the case off. Mine would go catatonic after as little as 10 minutes. I never managed to get enough cooling air in the right places without the case on, but it surely must be doable. Once overheated, I needed to leave it off for like 20 minutes before powering back on, inside the case.

If you can get a cellphone recording of the hard drive noises at power up, I can opine on its health. Put the mic right at the base of the monitor.

—Peter

P.S. Here’s mine right now, running the Office, the Programmer’s Calculator, and GNU emacs :-)
https://drive.google.com/open?id=1gLeI4Pc8qiKR3km_RuMXfiwqMBYPMv0h

[David Gesswein]

In article <68b37b82-e1c1-4aa7...@googlegroups.com>,

CRD <crdo...@gmail.com> wrote:
>
>I have a 7300 in my possession, it powers up with fans spinning and I
>can hear the harddrive being accessed but the CRT lights up to a solid
>green screen. And I have already reseated all my socketed chips,
>including the CPU, and traced my connections looking for broken traces,
>vias and bodge wires and found none.
>
>The computer did have loading bars when I originally acquired it, but
>has since refused to do anything but give a solid green screen.
>
>My question is: What are my options at this point? And is there any fix
>for this that I haven't tried yet?
>
>Any and all ideas are welcome, I'm at the end of my rope with it as of now.
>
>Thanks, CRD.

From HwNotes in http://www.unixpc.org/3b1/osu/documents/

When the machine is first started, the boot ROM goes though some tests before
it tries to boot. If one of these tests fails, the machine halts with the
number of the test on the LEDs. The LEDs are behind the gates on the left side
of the machine, near the front.

LED 1 Red
LED 2 Green
LED 3 Yellow
LED 4 Red (I guess they ran out of colors)

Test 4 3 2 1 Problem
1 off off off on Failed telephone initialization
2 off off on off Failed video RAM test
3 off off on on Failed map RAM test
4 off on off off Failed to set map RAM to unity map
5 off on off on Failed dynamic RAM test
6 off on on off Failed initialization
7 off on on on Failed to find loader on disk

I looked at mine. You see them sequence through a couple of the states as
it runs the tests. At the end they are all on while trying to boot.

> My question is: What are my options at this point? And is there any fix
> for this that I haven't tried yet?
>

What test equipment do you have such as volt meter, scope etc?
Have you checked voltages?

[Convergent MightyFrame]

CRD, may I ask where you are located? I have a large cache of AT&T Unix PC Parts, and I might be able to help you diagnose... If you are close enough to me, I could be persuaded to make a house call. I split my time between Las Vegas and Central Iowa.

[CRD]

I appreciate the offer, I am located in New York, so several hours away from your location in Iowa.

[CRD]

Thank you for the input Peter. I have yet to close up the machine back into it's housing, but I did record the spin up and spin down of the hard drive. It doesn't sound good, but I'm not entirely sure what I am listening for. I hear movement on spin up and a faint squealing on spin down. Both can be heard in the video I have linked below.

https://www.reddit.com/user/RetroProcessor18/comments/ew6p81/att_unix_pc_mfm_hard_drive_power_up_power_down/

-CRD

[pe...@transcend.aero]

The little “Bzzzt” sound at 16s should probably be more like “blurrp-biddle-biddle-biddle,” which is the typical MFM hard drive head calibration (I think that’s what is is doing) on power up. The high pitched, faint scraping sound at 34s could be the anti-static tab on the hard drive, but it may also be the read/write heads, having failed to retract properly, scraping on the platters.

So, IMHO there’s a lack of typical healthy MFM drive startup noises, a presence of concerning noises, but not definitive due to competing sounds from floppy and fan(s).

Next step would be to try to boot the diagnostic floppy, I think.

—Peter

[AJ Palmgren]

CRD, I just messaged you on redditt, and I'm in a good place to follow up with you to provide some help if you still would like it. I see you've posted here recently on other threads, so hopefully you're still out there.

Drop me an email to the address at http://mightyframe.blogspot.com/p/contact.html

Talk soon,
Best,
AJ