Anybody using the TI silent 703 terminal

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Jay Cotton

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Aug 20, 2021, 9:41:28 PM8/20/21
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I got on on ebay, and of course it's dead.

It will not post. I looked inside at the main board and there is an empty
socket U16. I think this is an eprom. If any one can confirm my suspicion
that would be very helpful.

I did find a complete schematic for the printer, and am planning a debug
session this weekend.

tnx
jc

Scott Dorsey

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Aug 21, 2021, 10:50:11 AM8/21/21
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In article <e722dd86-3b20-47a9...@googlegroups.com>,
Jay Cotton <lbmg...@gmail.com> wrote:
>I got on on ebay, and of course it's dead.

What does dead mean? No power light?

>It will not post. I looked inside at the main board and there is an empty
>socket U16. I think this is an eprom. If any one can confirm my suspicion
>that would be very helpful.

It was not at all unusual for people to design in extra eprom sockets in case
later revisions of the firmware bloated. If it looks like memory and the
pinout is right, it's likely an eprom but that doesn't mean anything is
missing.

>I did find a complete schematic for the printer, and am planning a debug
>session this weekend.

Then you should have no problem seeing with U16 is. The first thing is to
check power supply rails. It has been 40 years since I have worked on one
of these things but as I recall they have a weird rail for the thermal head.
But if you have no 5V, nothing will work.

As always with equipment of this vintage, suspect electrolytics and tantalum
capacitors before anything else. Beep out the supply rails before applying
power because shorted tantalums will cause collateral damage.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Jay Cotton

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Aug 22, 2021, 2:59:03 PM8/22/21
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Here is the situation now.

The power supplies all check out.
The clock circuit is working. (8.08mhz)
The reset circuit seems to be working.

The processor is dead. No activity at all.

I tried to find documentation for the TMS 7041 chip.
No luck there.

Kinda stuck at this point.

jc

Scott Dorsey

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Aug 22, 2021, 3:22:10 PM8/22/21
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Jay Cotton <lbmg...@gmail.com> wrote:
>Here is the situation now.
>
>The power supplies all check out.
>The clock circuit is working. (8.08mhz)
>The reset circuit seems to be working.
>
>The processor is dead. No activity at all.

So the buss isn't cycling? Do you see anything moving on the buss at all?

>I tried to find documentation for the TMS 7041 chip.
>No luck there.

There should be a TMS7000 databook online somewhere. There are various
different versions of the IC... I don't remember the difference between
the TMS7041 and TMS7040 offhand but the databook will tell you. It was
not one of the more popular microcontrollers but they were certainly out
there.

Do you have a logic analyzer?

Dennis Boone

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Aug 22, 2021, 4:13:16 PM8/22/21
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> I tried to find documentation for the TMS 7041 chip.

http://bitsavers.org/components/ti/TMS7000/1983_SPND001A_TI_TMS7000_Family_Data_Manual.pdf

De

Three Jeeps

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Aug 22, 2021, 10:03:44 PM8/22/21
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A quick read of the databook indicates that the CPU clock is suppose to be 2.5 MHz across pins 17,18. If the 8 Mhz is at the CPU clock pins, that is high. For processors of that era I would do o/c experiments and they usually fell apart around 105% of spec. Perhaps the reset line is frozen? Any activity on the address, data or r/w lines? Processor socketed? As asked earlier, got a logic analyzer?
J

Jay Cotton

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Aug 23, 2021, 12:42:55 AM8/23/21
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Several things pop out as I read through the data book.

1. 4k rom on board, and 128 bytes of ram on board the chip.
2. It is possible that the chip is looping on its internal code/ram polling a status
bit/byte before moving on to the next phase.
3. The 8Mhz clock is way high, and 2.5mhz is more likely. Need to drill in on that.
A side note here, things like clock into the chip come from a gate array, where the 8mhz crystal
is connected.

4. need to revisit the clock pins and document each one.
5. need to take a better look at the reset pin. wonder if reset is dodgy.

Jay Cotton

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Aug 23, 2021, 12:46:17 AM8/23/21
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Yes I have a logic analyzer (8 channels).

All of the chips are directly soldered to the board. With exception of U16.

No action on the address/data or r/w lines. But then the chip may be running internal code that is polling at I/O port
somewhere.

jc

Scott Dorsey

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Aug 23, 2021, 2:17:11 PM8/23/21
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Three Jeeps <jjhu...@gmail.com> wrote:
>A quick read of the databook indicates that the CPU clock is suppose to be =
>2.5 MHz across pins 17,18. If the 8 Mhz is at the CPU clock pins, that is =
>high.

Could be bad crystal. More likely bad decoupling capacitors on supply rails.

Jay Cotton

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Aug 23, 2021, 6:14:06 PM8/23/21
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Page 4-27 lists the max clockin to be 10.2 mhz. The CPU has an internal divide by
4 circuit. I guess the 8mhz clock is o.k.

Probing with a scope.

I see pin13 has (INT1) 76hz. It seems to conform to the description in the terminal manual.

No data buss or address buss action at all. The MC bit is 0, as documented in the terminal
manual, for full expansion mode.

Reset is a 1. I blipped it with a ground, and did not see any changes at all.

Here is an interesting point. The CLOCKOUT pin 2 is a . No clock. This may be set by the boot
ROM.

Three Jeeps

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Aug 23, 2021, 9:44:42 PM8/23/21
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I looked in the data book to see if the clk had a divider ckt but didn't find any. If you found one then ya, 8MHz would put it into specs. U16 is the processor? or the ROM? I am not at all familar with the thing you are working on.
I quickly gleaned that on startup the CPU does a data fetch at FFFF,FFFE for boot sequence and yet you dont see any bus activity? I'd have to read more about how the CPU operates to offer help.
I did a quick google search and sources of that chip seem to be long gone. I did come across a ref to Toshiba as a second source but had no luck finding any.
J

Andy Valencia

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Aug 24, 2021, 12:32:27 AM8/24/21
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Three Jeeps <jjhu...@gmail.com> writes:
> I quickly gleaned that on startup the CPU does a data fetch at FFFF,FFFE
> for boot sequence and yet you dont see any bus activity?

I feel like he should at least see the reset line blip on powerup.
Without that, it seems like something basic upstream has failed. As
somebody said, caps on the power rails, something like that.

Andy Valencia
Home page: https://www.vsta.org/andy/
To contact me: https://www.vsta.org/contact/andy.html

Jay Cotton

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Aug 24, 2021, 2:50:04 PM8/24/21
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My next official step will be to replace the power supply caps.
I doubt that this is the primary problem, but its not that hard to do.

WRT reset. The reset goes to a 1 after the power is applied. I have
not measured the delay. Should be about 500 usec after the power
rails are stable. Controlled by a custom package (why oh why) lm3905 timer.

WRT memory read at init. I will setup the analyzer and try to catch that.
Guess I will trigger on the rising edge of reset.

Scott Dorsey

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Aug 25, 2021, 9:49:24 PM8/25/21
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Jay Cotton <lbmg...@gmail.com> wrote:
>My next official step will be to replace the power supply caps.
>I doubt that this is the primary problem, but its not that hard to do.

That's not what I said. Check the decoupling capacitors on the logic.

It probably won't hurt to do the power supply caps in the process, mind you,
since they are almost certainly bad. But it's the logic decoupling that
may be keeping the processor from running right.

Jay Cotton

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Aug 25, 2021, 10:09:57 PM8/25/21
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Well, I am seeing a bit of racket on the +5 rail. So, a few bucks for caps seems
in order.

Bypass caps eh? I'll have a go at them also, the the power supply caps come in.

jc

Jay Cotton

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Dec 8, 2021, 9:33:43 PM12/8/21
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Closing out this discussion.

I did not get the 703 running, changing caps was not the solution. I suspect it may have had a
voltage spike or the wrong power supply attached or something like that.

However, this turns out not to be a complete disaster. I got another 703 (that works) and now I have
a source of parts for the running terminal.

For those interested, https://www.youtube.com/c/CuriousMarc has a series on the silent 703 that is
very interesting. Not to mention the resurrection of the Apollo guidance computer etc.


jc
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