Re: [M100] Model 100 Boot Issue?

[Stephen Adolph]

2VDC is extremely low for nicad voltage.  Should be much higher, especially
with a strong wall wart.
what happens if you desolder and remove the internal nicad?  Do you have
the ability to replace the nicad with an alternative?



Power switch on, Memory power on: M28 voltage potential between pin 7 and
pin 14 is 2.01 VDC.  Potential between pin 13 and 7 is 0VDC.

>
> -CH-
>

[M100] Model 100 Boot Issue?

[Charles Hudson]

Stephen wrote:

If M28 pin 13 has 2.13V, then I think that is enough to turn on T20.  Which
is why the power supply is "off".

So what I think this says is
* When you turn on the power switch (mem switch also on) the power supply
tries to start
* something triggers the PCS signal or the /RESET signal to clock M28 flip
flop
* the flip flop output at pin 13 turns on T28 , causing shut down.

Power switch on, Memory power on: M28 voltage potential between pin 7 and
pin 14 is 2.01 VDC.  Potential between pin 13 and 7 is 0VDC.

-CH-

[M100] Model 100 Boot Issue?

[Charles Hudson]

[M100] Model 100 Boot Issue?

[Charles Hudson]

Stephen,

Thank you again for your responses.  You pointed to M28 (an MN4013B
flip-flop on my board) as an indicator of a shutdown signal.  I tested M27
(an MN4011B 4-output NAND) and M28.  Neither has positive voltage at pin
14, and M28's pin 13 actually measures a few tenths less than 0VDC.

The choke and ferrite in the leads from the jack are OK; 8.06 VDC arrives
at the board and approximately this much makes it to the power switch.  I
checked the reset switch to see if it was shorted but it does not appear to
be so.

This may take me forever but at least it keeps my mind off my poison ivy
rash.

Thanks again,

-CH-

Re: [M100] Model 100 Boot Issue?

[Stephen Adolph]

I'll describe a scenario that once really stumped me.

When trying to power up the M100, I found it would start and instantly
stop.  Very strange.  I traced it to the /LPS signal triggering a soft
shutdown (like POWER OFF).

So, the implication is that it was a defect somewhere not related to the
power supply, that was causing the power supply to shutdown.

I will also say that I never really fixed it; I set it aside.

The point is, there are system level feedback loops that can make a power
supply appear to be defective.

If the power switch is ON and T20 is also biased ON (meaning M28 pin 13 is
HIGH) then it is being shut down by either RESET or PCS.




On Mon, Oct 19, 2020 at 6:46 AM Charles Hudson  wrote:

> My apologies.  Apparently I haven't been clear in describing the problem.
>
> I have three "slabs": It is my Model 100 that is not functioning
> properly.  It will sometimes boot but mostly does not display any life when
> I hit the power switch.
>
> I have verified that its AC adapter is the proper polarity and puts out >
> 6VDC, that the AA alkalines are fresh, that the memory backup battery has a
> full charge and that the memory battery switch is set to "on".
>
> I have also verified that in spite of these facts the CPU is not
> outputting a clock signal.  There was some question whether I was measuring
> the clock signal properly, but I was able to demonstrate measuring the
> clock signal on my Model 102.  Using the same frequency counter and
> technique, the Model 100 does not display a clock signal.
>
> The reason for this appears to be that the +5VDC supply to the CPU is only
> +0.23VDC.  The question now is what is causing this to occur.  Somewhere
> between the AC adapter's input jack and the CPU power is being lost.
>
> It will be a formidable task for me to identify which of  the components,
> which number in the hundreds and include capacitors, resistors, diodes,
> transformers and more, are failing.  But I'm learning as I go, and I thank
> you all for your suggestions.
>
> -CH-
>
>
> 
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> <#m_-5604703377747324575_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>

[M100] Model 100 Boot Issue?

[Charles Hudson]

My apologies.  Apparently I haven't been clear in describing the problem.

I have three "slabs": It is my Model 100 that is not functioning properly.
It will sometimes boot but mostly does not display any life when I hit the
power switch.

I have verified that its AC adapter is the proper polarity and puts out >
6VDC, that the AA alkalines are fresh, that the memory backup battery has a
full charge and that the memory battery switch is set to "on".

I have also verified that in spite of these facts the CPU is not outputting
a clock signal.  There was some question whether I was measuring the clock
signal properly, but I was able to demonstrate measuring the clock signal
on my Model 102.  Using the same frequency counter and technique, the Model
100 does not display a clock signal.

The reason for this appears to be that the +5VDC supply to the CPU is only
+0.23VDC.  The question now is what is causing this to occur.  Somewhere
between the AC adapter's input jack and the CPU power is being lost.

It will be a formidable task for me to identify which of  the components,
which number in the hundreds and include capacitors, resistors, diodes,
transformers and more, are failing.  But I'm learning as I go, and I thank
you all for your suggestions.

-CH-


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Re: [M100] Model 100 Boot Issue?

[Stephen Adolph]

Charles,
I guess I got off the tracks here, I didn't realize that you had issues
with +5V.
So, does the entire voltage rail sit at 0.235V?
I'll go back and read from the start

Re: [M100] Model 100 Boot Issue?

[Doug Jackson]

The CLK signal is a full TTL level output from the 8085, derived from the
clock generated by the crystal.  It is half of the crystal frequency -
Confirming that your 4.9152 Mhz crystal is running happily.

Your counter may simply not be sensitive enough to detect the crystal
signal directly, or it may place too great a load on the crystal.  I would
use an oscilloscope to look at the crystal voltage directly.  But as I said
above, you don't have to because you have confirmation that your oscillator
is running.

If you can see a 2.458 Mhz signal on CLK, then it means that your crystal
is absolutely oscillating.   You can simply check by gently lifting one leg
of the crystal, and your 2.458 Mhz signal will go away.

Kindest regards,

Doug Jackson

em: d...@doughq.com
ph: 0414 986878

Check out my awesome clocks at www.dougswordclocks.com
Follow my amateur radio adventures at vk1zdj.net

---

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On Mon, 19 Oct 2020 at 04:59, Stephen Adolph  wrote:

> Fantastic.  Well is the cpu has 5V and there is no clock at pin 37
> then...I would change the crystal.
> Of course the CPU needs ground.
>
> The crystal is fully passive
> If there was a problem with the connections on pin 1 or 2 that could also
> do it
>
>
>
>
>
> On Sunday, October 18, 2020, Charles Hudson  wrote:
>
>> Examining documentation for the Model 102 I found that the clock signal
>> is on pin 29 and a usable ground on pin 22.  With some wire-wrapped pins
>> and kynar AWG30 I hooked the 102's bus up to the frequency counter.  With
>> the 102 power off the frequency read 0.  With power on it read 2.458426
>> MHz.  I think we have established that the counter is capable of counting.
>>
>> The question remains why the Model 100 80C85 is not clocking: Is the X2
>> crystal at fault or is power not getting to the crystal?  Part of my
>> problem is that I don't know where to probe for voltages.  Suggestions
>> welcome.
>>
>> -CH-
>>
>> Pics of the test setup:
>> https://drive.google.com/file/d/11MY_V3-GAxTM3Pon__NEGR0pZzyrppx-/view?usp=sharing,
>>
>> https://drive.google.com/file/d/17opAgMdcpcEL_T_bLqT2AK1xe1yObKfV/view?usp=sharing,
>>
>> https://drive.google.com/file/d/1zqKWYKAxFqBcQ9c3CaxttLbERHVt5FSQ/view?usp=sharing
>>
>>
>>

[M100] Model 100 Boot Issue?

[Charles Hudson]

Stephen wrote:
" Well is the cpu has 5V and there is no clock at pin 37 then..."

However, the voltage between CPU pins 40 and 20 is 0.235VDC or so.  Too
little to light up anything.

Somewhere between the power input and the CPU there must be one or more
components that are failing.  Worse yet, SOMETIMES failing.  Finding them
is not my long suit but I'll give it a try.  The temptation is to blame the
electrolytics, but I thought they either work or they don't..

How to approach this?  Would you replace all the caps as a start?  Or
follow the power train and look for a place where the voltage is lower than
expected?

Thanks for suggestions.

-CH-

Re: [M100] Model 100 Boot Issue?

[Stephen Adolph]

Fantastic.  Well is the cpu has 5V and there is no clock at pin 37 then...I
would change the crystal.
Of course the CPU needs ground.

The crystal is fully passive
If there was a problem with the connections on pin 1 or 2 that could also
do it





On Sunday, October 18, 2020, Charles Hudson  wrote:

> Examining documentation for the Model 102 I found that the clock signal is
> on pin 29 and a usable ground on pin 22.  With some wire-wrapped pins and
> kynar AWG30 I hooked the 102's bus up to the frequency counter.  With the
> 102 power off the frequency read 0.  With power on it read 2.458426 MHz.  I
> think we have established that the counter is capable of counting.
>
> The question remains why the Model 100 80C85 is not clocking: Is the X2
> crystal at fault or is power not getting to the crystal?  Part of my
> problem is that I don't know where to probe for voltages.  Suggestions
> welcome.
>
> -CH-
>
> Pics of the test setup:  https://drive.google.com/file/
> d/11MY_V3-GAxTM3Pon__NEGR0pZzyrppx-/view?usp=sharing,
> https://drive.google.com/file/d/17opAgMdcpcEL_T_
> bLqT2AK1xe1yObKfV/view?usp=sharing, https://drive.google.com/file/d/
> 1zqKWYKAxFqBcQ9c3CaxttLbERHVt5FSQ/view?usp=sharing
>
>
>

[M100] Model 100 Boot Issue?

[Charles Hudson]

Examining documentation for the Model 102 I found that the clock signal is
on pin 29 and a usable ground on pin 22.  With some wire-wrapped pins and
kynar AWG30 I hooked the 102's bus up to the frequency counter.  With the
102 power off the frequency read 0.  With power on it read 2.458426 MHz.  I
think we have established that the counter is capable of counting.

The question remains why the Model 100 80C85 is not clocking: Is the X2
crystal at fault or is power not getting to the crystal?  Part of my
problem is that I don't know where to probe for voltages.  Suggestions
welcome.

-CH-

Pics of the test setup:
https://drive.google.com/file/d/11MY_V3-GAxTM3Pon__NEGR0pZzyrppx-/view?usp=sharing,
https://drive.google.com/file/d/17opAgMdcpcEL_T_bLqT2AK1xe1yObKfV/view?usp=sharing,
https://drive.google.com/file/d/1zqKWYKAxFqBcQ9c3CaxttLbERHVt5FSQ/view?usp=sharing

[M100] Model 100 Boot Issue?

[Charles Hudson]

Stephen asked:
"Are you using the EXT input or the TTL input at the back?"
...But, is there any way you can, with another M100, confirm that you can
measure 2.4576 MHz on pin 37?"

I was using the EXT input.  I do have another*, a Model 102 that is
working, and I can access the system bus from the port underneath.
Unfortunately I ordered 10 crystals this morning, but thank you for the
offer.

And thank you for your input.  I'll report my findings.

-CH-

* Also have an NEC PC-8300 but I think that would be different enough to
leave some doubt in any diagnosis.

Re: [M100] Model 100 Boot Issue?

[Stephen Adolph]

Thanks for sending the manual, interesting!
I don't think you can connect this counter to X2 directly.  It won't
oscillate.
Are you using the EXT input or the TTL input at the back?

But, is there any way you can, with another M100, confirm that you can
measure 2.4576 MHz on pin 37?  To me it feels like there is a ground issue,
or something.
The fact that this machine does start some times, suggests that you should
be able to get the counter connected and have M100 running, at the same
time.

I have a bag of 4.9152MHz crystals, if you need one.

The other way to measure clock is to connect to pins on the system bus.
Pin 15 is buffered clock.




On Sun, Oct 18, 2020 at 7:37 AM Charles Hudson  wrote:

> Stephen wrote:
>
> "
>
> * between 37 and ground you should have clock for sure.
> * If I were you I would confirm that your frequency counter reads the
> correct result when the M100 is working.
> * not sure how your counter works
>
> * X1 is for the RTC, won't prevent start up
> * X2 is the 4.9152 MHz crystal.
>
> "
> I repeated my tests with the frequency counter, first verifying its
> operation by connecting to a known-good source of oscillation (Velleman
> PMK147'1).  While connected to X2 with power on the frequency drifted from
> approximately 60 Hz to about 135 Hz, up and down.  With power off the
> frequency returned to 0 Hz.  I moved the counter contacts to pins 20 and 37
> of the CPU.  With power on I got 0 Hz.
>
> I will try replacing the X2 crystal next.
>
> -CH-
>
> Link to counter manual:
> https://drive.google.com/file/d/1Qpj-rVU-FyOG4KIyBXnG977CGlm0duFU/view?usp=sharing
>

[M100] Model 100 Boot Issue?

[Charles Hudson]

Stephen wrote:

"

* between 37 and ground you should have clock for sure.
* If I were you I would confirm that your frequency counter reads the
correct result when the M100 is working.
* not sure how your counter works

* X1 is for the RTC, won't prevent start up
* X2 is the 4.9152 MHz crystal.

"
I repeated my tests with the frequency counter, first verifying its
operation by connecting to a known-good source of oscillation (Velleman
PMK147'1).  While connected to X2 with power on the frequency drifted from
approximately 60 Hz to about 135 Hz, up and down.  With power off the
frequency returned to 0 Hz.  I moved the counter contacts to pins 20 and 37
of the CPU.  With power on I got 0 Hz.

I will try replacing the X2 crystal next.

-CH-

Link to counter manual:
https://drive.google.com/file/d/1Qpj-rVU-FyOG4KIyBXnG977CGlm0duFU/view?usp=sharing

Re: [M100] Model 100 Boot Issue?

[Robert J. Hutchins]

Try removing the RAM, one at a time…

 

From: M100 [mailto:m100-boun...@lists.bitchin100.com] On Behalf Of Charles 
Hudson
Sent: Saturday, October 17, 2020 2:14 PM
To: m100@lists.bitchin100.com
Subject: [M100] Model 100 Boot Issue?

 

Delving deeper into the mystery:  With no batteries in the tray and no adapter 
powering the unit I measured the voltage of the (nominally) 3.6V 80mah backup 
battery at 4.3 VDC.  I had replaced the original with this battery a few years 
ago and it appears to be in good shape.  (I bought mine on eBay).

 

I also checked the power switch and the adapter socket for continuity; both 
passed.  I unplugged the cable to the display and checked for corrosion; I 
can't see any evidence in the cable, the battery tray or the motherboard in 
that area.  I looked up crystal X1, which seemed to have a foreign substance 
around its base: either glue / insulator or something has leaked.  I don't know 
if there is anything in a crystal that could leak, but I couldn't test the 
crystal directly anyway.

 

Instead I found the 80C85 and located pins 1, 20 and 37, and attached a 
frequency counter to 20 and 37.  The counter was set to sweep from 1.5 MHz to 3 
MHZ.  With power applied to the motherboard the counter never "latched" on any 
frequency.

 

It's too soon to blame the crystal, though: Referring to the troubleshooting 
matrix #1 in the Service Manual, I checked everything listed up until I got to 
the "converter transformer", which was not referenced by part number.  I assume 
it is the one near the power switch, and I took a guess as to which was pin 1.  
If I guessed right, I did not find the expected voltage.

 

I removed and replaced C82 and C83 as recommended but that did not solve the 
problem.  I took some pictures for the benefit of any interested parties:  
https://drive.google.com/file/d/11gkvYUbYowW8TM8zglytiRFqBSvOLlmz/view?usp=sharing,
 
https://drive.google.com/file/d/1BoU6FzNwI6ZIIugVMHL1gieF5Mjrueil/view?usp=sharing,
 
https://drive.google.com/file/d/1M5wl4RLkGL4oSCo6qvCEW8CdmPPl_IVJ/view?usp=sharing,
 
https://drive.google.com/file/d/1g5F2R15J0sJ3UBLnhmxMWurtETGTnaaF/view?usp=sharing.

 

Thanks for your help so far:  Any further suggestions welcome.  

 

-CH-

 

 

 


 
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Re: [M100] Model 100 Boot Issue?

[Stephen Adolph]

Charles, some comments.

* you are right to leave pins 1 and 2 alone, they are very sensitive to
capacitance.
* between 37 and ground you should have clock for sure.
* If I were you I would confirm that your frequency counter reads the
correct result when the M100 is working.
* not sure how your counter works

* X1 is for the RTC, won't prevent start up
* X2 is the 4.9152 MHz crystal.

As I have been playing with different CPUs I have become aware that IF the
crystal doesnt oscillate correctly, you get absolutely nothing (of
course).  So, I do tend to check that the crystal is toggling by looking at
pin 37.



On Sat, Oct 17, 2020 at 5:14 PM Charles Hudson  wrote:

>
> Instead I found the 80C85 and located pins 1, 20 and 37, and attached a
> frequency counter to 20 and 37.  The counter was set to sweep from 1.5 MHz
> to 3 MHZ.  With power applied to the motherboard the counter never
> "latched" on any frequency.
>
>
>
>
> 
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>

[M100] Model 100 Boot Issue?

[Charles Hudson]

Delving deeper into the mystery:  With no batteries in the tray and no
adapter powering the unit I measured the voltage of the (nominally) 3.6V
80mah backup battery at 4.3 VDC.  I had replaced the original with this
battery a few years ago and it appears to be in good shape.  (I bought mine
on eBay).

I also checked the power switch and the adapter socket for continuity; both
passed.  I unplugged the cable to the display and checked for corrosion; I
can't see any evidence in the cable, the battery tray or the motherboard in
that area.  I looked up crystal X1, which seemed to have a foreign
substance around its base: either glue / insulator or something has
leaked.  I don't know if there is anything in a crystal that could leak,
but I couldn't test the crystal directly anyway.

Instead I found the 80C85 and located pins 1, 20 and 37, and attached a
frequency counter to 20 and 37.  The counter was set to sweep from 1.5 MHz
to 3 MHZ.  With power applied to the motherboard the counter never
"latched" on any frequency.

It's too soon to blame the crystal, though: Referring to the
troubleshooting matrix #1 in the Service Manual, I checked everything
listed up until I got to the "converter transformer", which was not
referenced by part number.  I assume it is the one near the power switch,
and I took a guess as to which was pin 1.  If I guessed right, I did not
find the expected voltage.

I removed and replaced C82 and C83 as recommended but that did not solve
the problem.  I took some pictures for the benefit of any interested
parties:
https://drive.google.com/file/d/11gkvYUbYowW8TM8zglytiRFqBSvOLlmz/view?usp=sharing,
https://drive.google.com/file/d/1BoU6FzNwI6ZIIugVMHL1gieF5Mjrueil/view?usp=sharing,
https://drive.google.com/file/d/1M5wl4RLkGL4oSCo6qvCEW8CdmPPl_IVJ/view?usp=sharing,
https://drive.google.com/file/d/1g5F2R15J0sJ3UBLnhmxMWurtETGTnaaF/view?usp=sharing
.

Thanks for your help so far:  Any further suggestions welcome.

-CH-




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Re: [M100] Model 100 Boot Issue?

[Joshua O'Keefe]

On Oct 17, 2020, at 11:05 AM, Erik van der Tier  wrote:
> Does anyone know where and what to get?

The one linked below is what I am using and it works beautifully.  Installation 
was not difficult.

https://www.arcadeshopper.com/wp/store/#!/NI-MH-3-6v-80Mah-replacement-battery/p/109811157/category=32594049

Re: [M100] Model 100 Boot Issue?

[Erik van der Tier]

Hi,

I’ve been having the same issue. But it sounds like it is worse on your 
machine. If it really is the backup battery, I’d like to know where to get a 
replacement. Does anyone know where and what to get?

Cheers,
   Erik

> On 17 Oct 2020, at 18:09, Charles Hudson  wrote:
> 
> 
> Following up on this issue:  Not being sure how the recharge circuit for the 
> memory backup battery works, I plugged in the AC adapter and left the 
> computer power switch in the ON position for 24 hours, then tested to see if 
> the battery was charged.  In multiple attempts there was one instance where 
> cycling the switch from OFF to ON resulted in a proper boot-up and menu 
> display.
> 
> Subsequent attempts all failed, however.  Thinking this may have been due to 
> a marginally-charged  backup battery, I left the machine connected to the AC 
> adapter for another 24 hours, this time with the switch in the OFF position.
> 
> When I turned the machine ON for the first time it booted to a menu.  I 
> selected BASIC and that loaded.  I entered a small for-next program and ran 
> it.  I saved the program and returned to the menu, where I selected it again 
> and it ran.  I returned to the menu again and powered down.  When I turned 
> the machine ON again nothing came up.
> 
> So far I know nothing, in other words, other than that the machine is capable 
> of booting, but does not do so consistently.  Next question is why.  Could be 
> the backup battery is low, could be the crystal won't start reliably, could 
> be a flaky power switch.  Probably is none of the above.
> 
> -CH-
> 
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Re: [M100] Model 100 Boot Issue?

[Gregory McGill]

if the backup battery is original. that's the likely culprit..  also..it's
going to leak.. if it's not already leaking..  replace it or clip it off
the board

On Sat, Oct 17, 2020 at 9:09 AM Charles Hudson  wrote:

> Following up on this issue:  Not being sure how the recharge circuit for
> the memory backup battery works, I plugged in the AC adapter and left the
> computer power switch in the ON position for 24 hours, then tested to see
> if the battery was charged.  In multiple attempts there was one instance
> where cycling the switch from OFF to ON resulted in a proper boot-up and
> menu display.
>
> Subsequent attempts all failed, however.  Thinking this may have been due
> to a marginally-charged  backup battery, I left the machine connected to
> the AC adapter for another 24 hours, this time with the switch in the OFF
> position.
>
> When I turned the machine ON for the first time it booted to a menu.  I
> selected BASIC and that loaded.  I entered a small for-next program and ran
> it.  I saved the program and returned to the menu, where I selected it
> again and it ran.  I returned to the menu again and powered down.  When I
> turned the machine ON again nothing came up.
>
> So far I know nothing, in other words, other than that the machine is
> capable of booting, but does not do so consistently.  Next question is
> why.  Could be the backup battery is low, could be the crystal won't start
> reliably, could be a flaky power switch.  Probably is none of the above.
>
> -CH-
>
>
> 
>  Virus-free.
> www.avast.com
> 
> <#m_-4182803861493036851_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>

[M100] Model 100 Boot Issue?

[Charles Hudson]

Following up on this issue:  Not being sure how the recharge circuit for
the memory backup battery works, I plugged in the AC adapter and left the
computer power switch in the ON position for 24 hours, then tested to see
if the battery was charged.  In multiple attempts there was one instance
where cycling the switch from OFF to ON resulted in a proper boot-up and
menu display.

Subsequent attempts all failed, however.  Thinking this may have been due
to a marginally-charged  backup battery, I left the machine connected to
the AC adapter for another 24 hours, this time with the switch in the OFF
position.

When I turned the machine ON for the first time it booted to a menu.  I
selected BASIC and that loaded.  I entered a small for-next program and ran
it.  I saved the program and returned to the menu, where I selected it
again and it ran.  I returned to the menu again and powered down.  When I
turned the machine ON again nothing came up.

So far I know nothing, in other words, other than that the machine is
capable of booting, but does not do so consistently.  Next question is
why.  Could be the backup battery is low, could be the crystal won't start
reliably, could be a flaky power switch.  Probably is none of the above.

-CH-


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[M100] Model 100 Boot Issue?

[Charles Hudson]

Josh,

Thank you for your response and for the link to the Model 100 Service
Manual.  I was unaware of its existence.

The machine is clean around the battery tray; there is no evidence of
leaking.  But I had been leaving the memory switch on and knowing what I
now know about its role in memory operation I can see that may be the
source of the problem.

I assumed that occasional operation with AC power and a set of alkaline AAs
would be enough to keep the NiCd charged but I never actually measured its
voltage.  I only measured the voltage from the AC supply, aka "wall wart".

I will report back what I find.

-CH-


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[M100] Model 100 Boot Issue?

[Charles Hudson]

I do have a scope and will check for crystal output.  Thanks for the
suggestion.

-CH-


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Re: [M100] Model 100 boot issue?

[Josh Malone]

On Tue, Oct 13, 2020 at 6:50 PM Charles Hudson  wrote:
>
>   and then checked the PSU voltage and replaced the AAs as first steps.

There are multiple voltages from the PSU; were they all okay? (+5Vdd,
-5Vee, +3 to +5 Vb)

> after reassembly I inserted a fresh set of batteries.  I must have left the 
> power switch "on" because
> when I turned it right side up I saw some characters on the display.

This indicates to me that the memory power switch had been left in the
ON position as well. This likely drained your memory NiCad beyond a
safe point. It will need at least 24 hours to attempt to recharge.
Again,the Vb (battery power rail) is critical here as this is what
actually powers the RAM chips. No RAM == unhappy computer.

You also mentioned re-seating the display cable. Does the connector
look physically okay? The proximity to the AA compartment often leads
battery corrosion to affect this cable. If this machine has *ever* had
any battery leaks, this cable is suspect, along with most of the power
supply circuit.

Download the service manual from
https://archive.org/details/TandyM100ServiceManual and follow the
troubleshooting guides in the back, keeping in mind the age of these
parts :)

Good luck!

-Josh

Re: [M100] Model 100 boot issue?

[Stephen Adolph]

I recently added 'check the crystal is oscillating'  to my list of basic
checks..
Can you scope it and see if you have 2.4MHZ clk?


On Tuesday, October 13, 2020, Charles Hudson  wrote:

> My Model 100 came to me with some problems and I have addressed what I can
> (replaced memory backup battery and the usual capacitors, for example) but
> this one has me stumped:  After reliable service for more than a year, a
> few months ago it simply would not light up.  I hit the reset button, of
> course, and then checked the PSU voltage and replaced the AAs as first
> steps.  I varied the display pot to see if it had been moved accidentally.
> None of this solved the problem.
>
> Once before it had displayed this problem and I had solved it then by
> splitting the case and unplugging / replugging the display cables.  I took
> it apart again and today after reassembly I inserted a fresh set of
> batteries.  I must have left the power switch "on" because when I turned it
> right side up I saw some characters on the display.  Not the usual menu,
> though.
>
> So I pressed the reset button, and the usual menu appeared , with a prompt
> below that seemed to relate to the code for the DVI: "Select ..."  I
> pressed the reset button again, and the display went blank.  I shut down,
> took out the batteries and turned off memory backup power for about 15
> seconds, replaced batteries, enabled memory power and powered up.  Still
> blank.
>
> I checked my reference materials because I faintly remembered there is a
> cold-start sequence.  I found it on line, at last: SHIFT+CTL+BREAK held
> down together, then press RESET.  That didn't work either.  No sign of life.
>
> I'm posting here in hopes someone has run across this problem and can
> diagnose it or suggest a direction for investigation. Thanks for any
> suggestions.
> -CH-
>
>
>
>
> 
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>

[M100] Model 100 boot issue?

[Charles Hudson]

My Model 100 came to me with some problems and I have addressed what I can
(replaced memory backup battery and the usual capacitors, for example) but
this one has me stumped:  After reliable service for more than a year, a
few months ago it simply would not light up.  I hit the reset button, of
course, and then checked the PSU voltage and replaced the AAs as first
steps.  I varied the display pot to see if it had been moved accidentally.
None of this solved the problem.

Once before it had displayed this problem and I had solved it then by
splitting the case and unplugging / replugging the display cables.  I took
it apart again and today after reassembly I inserted a fresh set of
batteries.  I must have left the power switch "on" because when I turned it
right side up I saw some characters on the display.  Not the usual menu,
though.

So I pressed the reset button, and the usual menu appeared , with a prompt
below that seemed to relate to the code for the DVI: "Select ..."  I
pressed the reset button again, and the display went blank.  I shut down,
took out the batteries and turned off memory backup power for about 15
seconds, replaced batteries, enabled memory power and powered up.  Still
blank.

I checked my reference materials because I faintly remembered there is a
cold-start sequence.  I found it on line, at last: SHIFT+CTL+BREAK held
down together, then press RESET.  That didn't work either.  No sign of life.

I'm posting here in hopes someone has run across this problem and can
diagnose it or suggest a direction for investigation. Thanks for any
suggestions.
-CH-




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