Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[perhaps...@gmail.com]

Hi,

Apologies for delay in providing an update — seems work can get in the way
of things sometimes.

As of now, still no change in life of the little M102 - no home screen
menu, no beep, contrast runs through full range from light to dark. LCD
cable tested and retested.

I have validated that there are signals going to/from where I understand
they should be (main ROM <> 1st 8k and other locations) and suspect that I
am caught in some sort of CPU or ROM loop (as mentioned). I do have a scope
on the way, and will be able to get more in-depth when it arrives and will
provide more details then.

As an aside, anyone every run into issues with the CPUs resistor packs? I’m
testing them in-circuit and they don’t appear to meet their specs - which
could be just fine, but I don’t know. Also, voltage is 4.9v on the CPU, ROM
+ RAM my assumption so far is that this is fine, but perhaps it really
needs 5v+ and is not tolerant of even small deviations. Clearly, I’m
fishing for solutions, but thought I’d ask anyhow.

In the meantime, I’m practicing patience and re-reviewing the schematic.
Something other than a physical connection seems to be at play.

Cheers,

Alan

On Fri, Jul 17, 2020 at 15:42 Stephen Adolph  wrote:

> my 2 cents;
> Worth it to see if you have valid signals at both the  main ROM and at
> each of the installed rams but most importantly the "top 8k". meaning the
> 8K RAM that is closest to the system socket.
>
> if there happens to be a cracked track on the PCB, that affects the memory
> subsystem, you will get this kind of behaviour.
>
> It would be reasonable for the CPU to end up in a loop under this sort of
> condition as well.
>
> Yes, I have seen this happen on my fleet of laptops.  Not common in
> general, but more common on T102 and T200 for some reason.
>
>

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Chris Fezzler]

 The quality of the information shared on this listserv is off the charts.I 
joined many moons ago when the focus was on simply using the Model T platform.  
The transformative innovation, while often over my head, has been remarkable to 
watch, support and use.


On Friday, July 17, 2020, 03:17:23 PM EDT, Jeffrey Birt 
 wrote:  
 
 
M28 has to do with the low voltage reset. If pin 13 of M28 is low, then you are 
not in low voltage reset so T20 will not be switched on which kills the power 
supply. 

  

Generally having a screen with all dark elements with these Hitachi type LCD 
controllers means the LCD is not being initialized properly. After the driver 
chips are initialized, they will turn off until told to turn on. 

  

Given that ‘BEEP’ does not work it would seem like the LCD is not being 
initialized and the boot code in ROM is stuck in a loop waiting for it. The 
following text is from an email conversation I had with group member Ian (who 
developed the M100/T102 test harness). It was nice of him to pass on this 
information about the LCD boot process and I hope it helps you with your 
troubleshooting.

  

Jeff

  

---

LCD Initialization – From Ian

The boot routines check the LCD is in "up mode" and the busy and reset bits are 
correct.  If this is not the case it will keep looping forever, i.e. the 
machine will not boot. If the screen is blank, blind type in ‘beep’ and press 
return. If this works you know the machine is booting and that the LCD is 
returning the correct status. 

The LCD is split into 10 RAM like ICs that deal with the columns and then two 
row chips.  The CS20-29 lines are the individual column chip selects and CS1 is 
the common select that allows all the ICs to be written in one operation 
usually for refresh/clearing or individually with the relevant CS20-29 line.  

If the screen is remaining dark this is the post reset condition and none of 
the chips are being correctly set up and/or cleared with a screen bit data 
write.  If one of the CS20-29 lines had failed I would expect to see blocks of 
the screen with garbage., in fact it would be blank as part of the 
initialization turns on the ICs for display.   I was surmising that the CS1 
line might have failed which is preventing the screen from being correctly 
initialized.  

But thinking further if the D/I line has failed low then it would allow the 
screen status to be read back and of course set up for the correct direction 
mode – so the status would be correct.  However, when writing screen bit data, 
it would fail to write anything to the screen.  So, it could be D/I- is stuck 
low and only allowing Instructions to be written but not allowing screen bit 
data to be written. This could mean the A8 track is broken and not connected to 
the LCD.  

If WR/RD had failed, then it would not initialize, and the screen would not 
work - it would hang. I think the LCD ICs reset to down mode and not up mode 
which the boot sequence wants to see. 

---

  

From: M100  On Behalf Of perhaps...@gmail.com
Sent: Friday, July 17, 2020 1:15 PM
To: m...@bitchin100.com
Subject: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

  

Thanks Jeff. I have revisited all the documented diagnostics in the service 
manual, and checked/re-checked all the voltages, reset circuit and LCD.

  

The current state is that the system has correct voltages in both 
power-on/memory-on and power-off/memory-on modes. The LCD works, in as much as 
it can be adjusted from light to dark contrast (full black screen) but displays 
nothing otherwise.

  

I have checked the reset signal on the ICs, and see only one anomaly in M28 
(Flip-flop) where:
   
   - Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset button 
in/active)
   - Pin #13 (Q) - 0v (reset button out), 0v (reset button in/active). Neither 
state shows either high or low.
   - I will note that since I don't have a logic chart, I'm not sure if this is 
normal or an anomaly.

In addition, I have checked T9, T10, T11 and T25 and with the exception of T9 
all show what I assume is correct behavior on the Emitter -- H/4.9v (reset 
out), L/0v (reset in/active). 
   
   - T9 however shows L/0.3v (reset out), H/2.7v (reset in/active). 
   - A check of all the transistors via my multimeter (diode test) shows they 
all appear to be OK (0.7v from B to E, and B to C). So T9's behavior might be 
good, but without anything to compare I don't know.

I also checked the keyboard, in case it was not working and thus the 
 signal would never be seen -- as best as I can tell 
it works.

  

I have checked/rechecked all flat cables connecting LCD + Keyboard, and they 
all appear to have no bad connectors or breaks along the cable (checked in 
various positions to ensure not an intermittent break).

  

Additionally, I have fully charged the memory battery, turned the system off, 
removed the AAAs (I have no externa

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Stephen Adolph]

my 2 cents;
Worth it to see if you have valid signals at both the  main ROM and at each
of the installed rams but most importantly the "top 8k". meaning the 8K RAM
that is closest to the system socket.

if there happens to be a cracked track on the PCB, that affects the memory
subsystem, you will get this kind of behaviour.

It would be reasonable for the CPU to end up in a loop under this sort of
condition as well.

Yes, I have seen this happen on my fleet of laptops.  Not common in
general, but more common on T102 and T200 for some reason.

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[perhaps...@gmail.com]

Thanks Jeff B, & Bert P.

I will review the note from Ian, and in the meantime did recheck the CPU
(using a logic probe and my BK Precision multimeter).

Crystal Oscillators

   - X1 = 32.76 khz
   - X2 = 4.916 mhz

M19/CPU

   - #1 = constant signal
   - #2 = 4.916 mhz
   - #12-19 (AD0-7) = detect a pulse on all lines
   - #21-28 (A8-15) = detect a pulse on all lines
   - #37 (clk) = 2.458 mhz
   - #40 (vdd) = 4.929 v
   - noted activity or sorts on all other pins.

>From the above it appears the CPU is active, of course without an
oscilloscope (on my list to get), I can only confirm activity present - not
whether good/valid. My next steps are to recheck the physical LCD cable,
and then dive into the "LCD Initialization – From Ian" and see if I can
identify anything there.

Really appreciate the response, it has really helped encourage me onward.
I'll check back with what I discover, and welcome more ideas in the interim.

Cheers, Alan

On Fri, Jul 17, 2020 at 12:17 PM Bert Put  wrote:

> Hi Alan,
>
> I'm with Jeff on this one.  So far you've shown that you've tested
> voltages, cables, even the LCD contrast pot, but you haven't really
> talked about the logic side.  You mentioned you replaced all the RAM
> (even installing sockets), as well as re-capping the board, but so far I
> haven't seen anything to verify that the system clock is running, or
> that the CPU is running.
>
> It will be hard to do this without an oscilloscope but maybe you have a
> frequency counter or something that you can use to verify the clock is
> running, and that the CPU is running?  Jeff's video shows how you can
> check for activity on the address and data lines; without that activity
> literally nothing will happen on the board.  Good luck.
>
> Cheers,Bert (not Jeff :-)
>
>
> On 7/17/20 2:07 PM, perhaps...@gmail.com wrote:
> > Hi Matt
> >
> > Thanks. I have found similar issue with the LCD cable on the ends,
> > corrected and carefully reinserted. I will take another look, and redo
> > continuity from connector to connector.
> >
> > If I can find a flat ribbon with the correct specs, I’ll also try to
> > order a replacement.
> >
> > Here’s to hoping I missed something with the cable!
> >
> > Alan
> >
> >
> > On Fri, Jul 17, 2020 at 11:52 Matthew Stock  > > wrote:
> >
> > Hi Alan,
> >
> > I was working through a similar issue recently.  Fortunately, I had
> > access to a logic analyzer and was able to confirm that the CPU was
> > operating properly, and even where in the ROM it was looping.  Once
> > I was able to determine it was waiting for the LCD status to change,
> > I rechecked the cable and found that several pins on the cable end
> > that slide into the LCD connector had delaminated and folded over.
> > I was able to smooth them out and insert the cable and the LCD
> > behaved after that.
> >
> > I know you mentioned that you already checked the cable, but it
> > might be worth checking the ends and/or run a continuity test from
> > the soldered connector pins on the motherboard and the LCD board to
> > be certain you have electrical connectivity all the way through.
> >
> > Matt
> >
> >
> > On Fri, Jul 17, 2020 at 2:15 PM perhaps...@gmail.com
> >   > > wrote:
> >
> > Thanks Jeff. I have revisited all the documented diagnostics in
> > the service manual, and checked/re-checked all the voltages,
> > reset circuit and LCD.
> >
> > The current state is that the system has correct voltages in
> > both power-on/memory-on and power-off/memory-on modes. The LCD
> > works, in as much as it can be adjusted from light to dark
> > contrast (full black screen) but displays nothing otherwise.
> >
> > I have checked the reset signal on the ICs, and see only one
> > anomaly in M28 (Flip-flop) where:
> >
> >   * Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset
> > button in/active)
> >   * Pin #13 (Q) - 0v (reset button out), 0v (reset button
> > in/active). Neither state shows either high or low.
> >   * I will note that since I don't have a logic chart, I'm not
> > sure if this is normal or an anomaly.
> >
> > In addition, I have checked T9, T10, T11 and T25 and with the
> > exception of T9 all show what I assume is correct behavior on
> > the Emitter -- H/4.9v (reset out), L/0v (reset in/active).
> >
> >   * T9 however shows L/0.3v (reset out), H/2.7v (reset
> in/active).
> >   * A check of all the transistors via my multimeter (diode
> > test) shows they all appear to be OK (0.7v from B to E, and
> > B to C). So T9's behavior might be good, but without
> > anything to compare I don't know.
> >
> > I also checked the keyboard, in case it was not working an

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Jeffrey Birt]

>>Cheers,Bert (not Jeff :-)

There can never be too many Berts, Birts, Burts, 😊

Jeff Birt


 

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Brian K. White]

i.e. the machine will not boot. If the screen is blank, blind type in 
‘beep’ and press return. If this works you know the machine is booting 

Press Enter once to get into BASIC first.

--
bkw

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Jeffrey Birt]

M28 has to do with the low voltage reset. If pin 13 of M28 is low, then you are 
not in low voltage reset so T20 will not be switched on which kills the power 
supply. 

 

Generally having a screen with all dark elements with these Hitachi type LCD 
controllers means the LCD is not being initialized properly. After the driver 
chips are initialized, they will turn off until told to turn on. 

 

Given that ‘BEEP’ does not work it would seem like the LCD is not being 
initialized and the boot code in ROM is stuck in a loop waiting for it. The 
following text is from an email conversation I had with group member Ian (who 
developed the M100/T102 test harness). It was nice of him to pass on this 
information about the LCD boot process and I hope it helps you with your 
troubleshooting.

 

Jeff

 

---

LCD Initialization – From Ian

The boot routines check the LCD is in "up mode" and the busy and reset bits are 
correct.  If this is not the case it will keep looping forever, i.e. the 
machine will not boot. If the screen is blank, blind type in ‘beep’ and press 
return. If this works you know the machine is booting and that the LCD is 
returning the correct status. 

The LCD is split into 10 RAM like ICs that deal with the columns and then two 
row chips.  The CS20-29 lines are the individual column chip selects and CS1 is 
the common select that allows all the ICs to be written in one operation 
usually for refresh/clearing or individually with the relevant CS20-29 line.  

If the screen is remaining dark this is the post reset condition and none of 
the chips are being correctly set up and/or cleared with a screen bit data 
write.  If one of the CS20-29 lines had failed I would expect to see blocks of 
the screen with garbage., in fact it would be blank as part of the 
initialization turns on the ICs for display.   I was surmising that the CS1 
line might have failed which is preventing the screen from being correctly 
initialized.  

But thinking further if the D/I line has failed low then it would allow the 
screen status to be read back and of course set up for the correct direction 
mode – so the status would be correct.  However, when writing screen bit data, 
it would fail to write anything to the screen.  So, it could be D/I- is stuck 
low and only allowing Instructions to be written but not allowing screen bit 
data to be written. This could mean the A8 track is broken and not connected to 
the LCD.  

If WR/RD had failed, then it would not initialize, and the screen would not 
work - it would hang. I think the LCD ICs reset to down mode and not up mode 
which the boot sequence wants to see. 

---

 

From: M100  On Behalf Of perhaps...@gmail.com
Sent: Friday, July 17, 2020 1:15 PM
To: m...@bitchin100.com
Subject: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

 

Thanks Jeff. I have revisited all the documented diagnostics in the service 
manual, and checked/re-checked all the voltages, reset circuit and LCD.

 

The current state is that the system has correct voltages in both 
power-on/memory-on and power-off/memory-on modes. The LCD works, in as much as 
it can be adjusted from light to dark contrast (full black screen) but displays 
nothing otherwise.

 

I have checked the reset signal on the ICs, and see only one anomaly in M28 
(Flip-flop) where:

*   Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset button 
in/active)
*   Pin #13 (Q) - 0v (reset button out), 0v (reset button in/active). 
Neither state shows either high or low.
*   I will note that since I don't have a logic chart, I'm not sure if this 
is normal or an anomaly.

In addition, I have checked T9, T10, T11 and T25 and with the exception of T9 
all show what I assume is correct behavior on the Emitter -- H/4.9v (reset 
out), L/0v (reset in/active). 

*   T9 however shows L/0.3v (reset out), H/2.7v (reset in/active). 
*   A check of all the transistors via my multimeter (diode test) shows 
they all appear to be OK (0.7v from B to E, and B to C). So T9's behavior might 
be good, but without anything to compare I don't know.

I also checked the keyboard, in case it was not working and thus the 
 signal would never be seen -- as best as I can tell 
it works.

 

I have checked/rechecked all flat cables connecting LCD + Keyboard, and they 
all appear to have no bad connectors or breaks along the cable (checked in 
various positions to ensure not an intermittent break).

 

Additionally, I have fully charged the memory battery, turned the system off, 
removed the AAAs (I have no external power supply), turned memory off for 15+ 
mins and repowered the unit. No change in behaviour. Blind  followed by 
typing B E E P doesn't work, and if I leave the unit powered on, power-save 
does not turn the unit off.

 

If the CPU is waiting for the LCD, and stuck in a loop how do I resolve this? 
If it is related to M28 and T11 then

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Bert Put]

Hi Alan,

I'm with Jeff on this one.  So far you've shown that you've tested
voltages, cables, even the LCD contrast pot, but you haven't really
talked about the logic side.  You mentioned you replaced all the RAM
(even installing sockets), as well as re-capping the board, but so far I
haven't seen anything to verify that the system clock is running, or
that the CPU is running.

It will be hard to do this without an oscilloscope but maybe you have a
frequency counter or something that you can use to verify the clock is
running, and that the CPU is running?  Jeff's video shows how you can
check for activity on the address and data lines; without that activity
literally nothing will happen on the board.  Good luck.

Cheers,Bert (not Jeff :-)


On 7/17/20 2:07 PM, perhaps...@gmail.com wrote:
> Hi Matt 
> 
> Thanks. I have found similar issue with the LCD cable on the ends,
> corrected and carefully reinserted. I will take another look, and redo
> continuity from connector to connector. 
> 
> If I can find a flat ribbon with the correct specs, I’ll also try to
> order a replacement. 
> 
> Here’s to hoping I missed something with the cable!
> 
> Alan
> 
> 
> On Fri, Jul 17, 2020 at 11:52 Matthew Stock  > wrote:
> 
> Hi Alan,
> 
> I was working through a similar issue recently.  Fortunately, I had
> access to a logic analyzer and was able to confirm that the CPU was
> operating properly, and even where in the ROM it was looping.  Once
> I was able to determine it was waiting for the LCD status to change,
> I rechecked the cable and found that several pins on the cable end
> that slide into the LCD connector had delaminated and folded over. 
> I was able to smooth them out and insert the cable and the LCD
> behaved after that.
> 
> I know you mentioned that you already checked the cable, but it
> might be worth checking the ends and/or run a continuity test from
> the soldered connector pins on the motherboard and the LCD board to
> be certain you have electrical connectivity all the way through.
> 
> Matt
> 
> 
> On Fri, Jul 17, 2020 at 2:15 PM perhaps...@gmail.com
>   > wrote:
> 
> Thanks Jeff. I have revisited all the documented diagnostics in
> the service manual, and checked/re-checked all the voltages,
> reset circuit and LCD.
> 
> The current state is that the system has correct voltages in
> both power-on/memory-on and power-off/memory-on modes. The LCD
> works, in as much as it can be adjusted from light to dark
> contrast (full black screen) but displays nothing otherwise.
> 
> I have checked the reset signal on the ICs, and see only one
> anomaly in M28 (Flip-flop) where:
> 
>   * Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset
> button in/active)
>   * Pin #13 (Q) - 0v (reset button out), 0v (reset button
> in/active). Neither state shows either high or low.
>   * I will note that since I don't have a logic chart, I'm not
> sure if this is normal or an anomaly.
> 
> In addition, I have checked T9, T10, T11 and T25 and with the
> exception of T9 all show what I assume is correct behavior on
> the Emitter -- H/4.9v (reset out), L/0v (reset in/active). 
> 
>   * T9 however shows L/0.3v (reset out), H/2.7v (reset in/active). 
>   * A check of all the transistors via my multimeter (diode
> test) shows they all appear to be OK (0.7v from B to E, and
> B to C). So T9's behavior might be good, but without
> anything to compare I don't know.
> 
> I also checked the keyboard, in case it was not working and thus
> the  signal would never be seen -- as
> best as I can tell it works.
> 
> I have checked/rechecked all flat cables connecting LCD +
> Keyboard, and they all appear to have no bad connectors or
> breaks along the cable (checked in various positions to ensure
> not an intermittent break).
> 
> Additionally, I have fully charged the memory battery, turned
> the system off, removed the AAAs (I have no external power
> supply), turned memory off for 15+ mins and repowered the unit.
> No change in behaviour. Blind  followed by typing B E E P
> doesn't work, and if I leave the unit powered on,
> power-save does not turn the unit off.
> 
> If the CPU is waiting for the LCD, and stuck in a loop how do I
> resolve this? If it is related to M28 and T11 then I can start
> with replacing T11. However, I'm reluctant to replace more
> parts, as full recap, new X1 and X2 and D13 have not changed the
> behavior so far.
> 
> At this point, I'm at a loss and would welcome advice - I really
> do w

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[perhaps...@gmail.com]

Hi Matt

Thanks. I have found similar issue with the LCD cable on the ends,
corrected and carefully reinserted. I will take another look, and redo
continuity from connector to connector.

If I can find a flat ribbon with the correct specs, I’ll also try to order
a replacement.

Here’s to hoping I missed something with the cable!

Alan


On Fri, Jul 17, 2020 at 11:52 Matthew Stock  wrote:

> Hi Alan,
>
> I was working through a similar issue recently.  Fortunately, I had access
> to a logic analyzer and was able to confirm that the CPU was operating
> properly, and even where in the ROM it was looping.  Once I was able to
> determine it was waiting for the LCD status to change, I rechecked the
> cable and found that several pins on the cable end that slide into the LCD
> connector had delaminated and folded over.  I was able to smooth them out
> and insert the cable and the LCD behaved after that.
>
> I know you mentioned that you already checked the cable, but it might be
> worth checking the ends and/or run a continuity test from the soldered
> connector pins on the motherboard and the LCD board to be certain you have
> electrical connectivity all the way through.
>
> Matt
>
>
> On Fri, Jul 17, 2020 at 2:15 PM perhaps...@gmail.com 
> wrote:
>
>> Thanks Jeff. I have revisited all the documented diagnostics in the
>> service manual, and checked/re-checked all the voltages, reset circuit and
>> LCD.
>>
>> The current state is that the system has correct voltages in both
>> power-on/memory-on and power-off/memory-on modes. The LCD works, in as much
>> as it can be adjusted from light to dark contrast (full black screen) but
>> displays nothing otherwise.
>>
>> I have checked the reset signal on the ICs, and see only one anomaly in
>> M28 (Flip-flop) where:
>>
>>- Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset button
>>in/active)
>>- Pin #13 (Q) - 0v (reset button out), 0v (reset button in/active).
>>Neither state shows either high or low.
>>- I will note that since I don't have a logic chart, I'm not sure if
>>this is normal or an anomaly.
>>
>> In addition, I have checked T9, T10, T11 and T25 and with the exception
>> of T9 all show what I assume is correct behavior on the Emitter -- H/4.9v
>> (reset out), L/0v (reset in/active).
>>
>>- T9 however shows L/0.3v (reset out), H/2.7v (reset in/active).
>>- A check of all the transistors via my multimeter (diode test) shows
>>they all appear to be OK (0.7v from B to E, and B to C). So T9's behavior
>>might be good, but without anything to compare I don't know.
>>
>> I also checked the keyboard, in case it was not working and thus the
>>  signal would never be seen -- as best as I can
>> tell it works.
>>
>> I have checked/rechecked all flat cables connecting LCD + Keyboard, and
>> they all appear to have no bad connectors or breaks along the cable
>> (checked in various positions to ensure not an intermittent break).
>>
>> Additionally, I have fully charged the memory battery, turned the system
>> off, removed the AAAs (I have no external power supply), turned memory off
>> for 15+ mins and repowered the unit. No change in behaviour. Blind 
>> followed by typing B E E P doesn't work, and if I leave the unit powered
>> on, power-save does not turn the unit off.
>>
>> If the CPU is waiting for the LCD, and stuck in a loop how do I resolve
>> this? If it is related to M28 and T11 then I can start with replacing T11.
>> However, I'm reluctant to replace more parts, as full recap, new X1 and X2
>> and D13 have not changed the behavior so far.
>>
>> At this point, I'm at a loss and would welcome advice - I really do want
>> to get this fully functional. Thanks in advance. FYI I'm more than happy to
>> talk real time with anyone offline too.
>>
>> Cheers,
>>
>> Alan
>>
>>
>> On Fri, Jul 3, 2020 at 5:10 PM Jeffrey Birt 
>> wrote:
>>
>>> One other thing I forgot to mention. I started a video series on general
>>> troubleshooting methodology for vintage computers. The idea is to cover the
>>> troubleshooting process rather than the repair of a specific computer. The
>>> first video is about evaluation of the computer and getting yourself
>>> started down the right path.
>>>
>>>
>>>
>>> https://www.youtube.com/playlist?list=PLegscpHOheJt_EpuPs9hfBpOJ5elRhYvw
>>>
>>>
>>>
>>> Jeff Birt
>>>
>>>
>>>
>>> *From:* M100  *On Behalf Of *
>>> perhaps...@gmail.com
>>> *Sent:* Friday, July 3, 2020 6:28 PM
>>> *To:* m...@bitchin100.com
>>> *Subject:* Re: [M100] M102, Black Screen, Help!
>>>
>>>
>>>
>>> Thanks Jeff.
>>>
>>>
>>>
>>> On Fri, Jul 3, 2020 at 5:27 AM Jeffrey Birt 
>>> wrote:
>>>
>>> Have you done a hard reset? Ctrl+Break+Reset button. Have you checked
>>> adjust the screen contrast pot?
>>>
>>>
>>>
>>

Re: [M100] Troubleshooting M102 (Was: M102, Black Screen, Help!)

[Matthew Stock]

Hi Alan,

I was working through a similar issue recently.  Fortunately, I had access
to a logic analyzer and was able to confirm that the CPU was operating
properly, and even where in the ROM it was looping.  Once I was able to
determine it was waiting for the LCD status to change, I rechecked the
cable and found that several pins on the cable end that slide into the LCD
connector had delaminated and folded over.  I was able to smooth them out
and insert the cable and the LCD behaved after that.

I know you mentioned that you already checked the cable, but it might be
worth checking the ends and/or run a continuity test from the soldered
connector pins on the motherboard and the LCD board to be certain you have
electrical connectivity all the way through.

Matt


On Fri, Jul 17, 2020 at 2:15 PM perhaps...@gmail.com 
wrote:

> Thanks Jeff. I have revisited all the documented diagnostics in the
> service manual, and checked/re-checked all the voltages, reset circuit and
> LCD.
>
> The current state is that the system has correct voltages in both
> power-on/memory-on and power-off/memory-on modes. The LCD works, in as much
> as it can be adjusted from light to dark contrast (full black screen) but
> displays nothing otherwise.
>
> I have checked the reset signal on the ICs, and see only one anomaly in
> M28 (Flip-flop) where:
>
>- Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset button
>in/active)
>- Pin #13 (Q) - 0v (reset button out), 0v (reset button in/active).
>Neither state shows either high or low.
>- I will note that since I don't have a logic chart, I'm not sure if
>this is normal or an anomaly.
>
> In addition, I have checked T9, T10, T11 and T25 and with the exception of
> T9 all show what I assume is correct behavior on the Emitter -- H/4.9v
> (reset out), L/0v (reset in/active).
>
>- T9 however shows L/0.3v (reset out), H/2.7v (reset in/active).
>- A check of all the transistors via my multimeter (diode test) shows
>they all appear to be OK (0.7v from B to E, and B to C). So T9's behavior
>might be good, but without anything to compare I don't know.
>
> I also checked the keyboard, in case it was not working and thus the
>  signal would never be seen -- as best as I can
> tell it works.
>
> I have checked/rechecked all flat cables connecting LCD + Keyboard, and
> they all appear to have no bad connectors or breaks along the cable
> (checked in various positions to ensure not an intermittent break).
>
> Additionally, I have fully charged the memory battery, turned the system
> off, removed the AAAs (I have no external power supply), turned memory off
> for 15+ mins and repowered the unit. No change in behaviour. Blind 
> followed by typing B E E P doesn't work, and if I leave the unit powered
> on, power-save does not turn the unit off.
>
> If the CPU is waiting for the LCD, and stuck in a loop how do I resolve
> this? If it is related to M28 and T11 then I can start with replacing T11.
> However, I'm reluctant to replace more parts, as full recap, new X1 and X2
> and D13 have not changed the behavior so far.
>
> At this point, I'm at a loss and would welcome advice - I really do want
> to get this fully functional. Thanks in advance. FYI I'm more than happy to
> talk real time with anyone offline too.
>
> Cheers,
>
> Alan
>
>
> On Fri, Jul 3, 2020 at 5:10 PM Jeffrey Birt  wrote:
>
>> One other thing I forgot to mention. I started a video series on general
>> troubleshooting methodology for vintage computers. The idea is to cover the
>> troubleshooting process rather than the repair of a specific computer. The
>> first video is about evaluation of the computer and getting yourself
>> started down the right path.
>>
>>
>>
>> https://www.youtube.com/playlist?list=PLegscpHOheJt_EpuPs9hfBpOJ5elRhYvw
>>
>>
>>
>> Jeff Birt
>>
>>
>>
>> *From:* M100  *On Behalf Of *
>> perhaps...@gmail.com
>> *Sent:* Friday, July 3, 2020 6:28 PM
>> *To:* m...@bitchin100.com
>> *Subject:* Re: [M100] M102, Black Screen, Help!
>>
>>
>>
>> Thanks Jeff.
>>
>>
>>
>> On Fri, Jul 3, 2020 at 5:27 AM Jeffrey Birt 
>> wrote:
>>
>> Have you done a hard reset? Ctrl+Break+Reset button. Have you checked
>> adjust the screen contrast pot?
>>
>>
>>
>