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Black Screen issue with Colecovision


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#26 vgcollector OFFLINE  

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Posted Mon Feb 11, 2019 5:09 PM

I am sorry I did not received any notifications after my last input.
I see you have been making significant progress and happy you have been assisted by a true expert (childofcv).

Did you say you have 3 colecovisions doing the same thing?

Before you do anything else, I would try a different tv set.
Just my 2 cents

Regards!

Al

I have used the tv set with my working Colecovision and it does fine. I am pretty good at eliminating problem possibilities.I use my good Colecovision to test the RF cable, TV, and power supply. I hope to test with the logic probe before the end of the week. Thanks for your assistance.

 

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#27 alortegac OFFLINE  

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Posted Mon Feb 11, 2019 5:12 PM

Ok, then I misunderstood you said you have 3 consoles doing the same black screen.(?)

#28 vgcollector OFFLINE  

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Posted Mon Feb 11, 2019 6:04 PM

You had it right. I have one working one and then 3 with the same black screen issue. Thanks



#29 vgcollector OFFLINE  

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Posted Mon Feb 18, 2019 6:39 AM

Connect the black lead to ground.  If you connect it to -5 and +5, that would be a 10V difference and would probably kill the probe.  Don't try to probe negative or +12V lines with it.

 

As long as you know what to expect, it's useful.  It can certainly tell you if the clock inputs are working (flashing lights), and if the +5 and gnd pins are good.  You can poke at data and address lines to see if any communication is going through the system.  For instance, the RFSH, M1, and MREQ lines from the processor should always be blinking.  Any clock line should be blinking.  If any data or address line is making it to the chip, chances are it will be blinking too.  The higher address lines (A15 through A10 or so) may not be too active, especially without a cartridge in.

 

Chip selects are trickier though, as they will only go low when that particular chip is singled out for communication.  The ROM chip's CS pin will probably be blinking though, possibly even both SRAM chips.  Audio and video output won't be digital, so who knows what the probe would say looking at any of them.

 

As a start, look at U22 pins 2, 4, 6, 8 and 10.  They should be blinking.  Same for U8 pins 6, 5, 8 and 9.  Just for grins, U8 pin 13 should be high and pin 7 should be low, though it's because these are hard-wired to power and ground respectively.

 

U7 pin 4 should be blinking.  Pins 11 and 12 should be low and U7 pin 10 should be high.

Getting closer to using the probe, but I don't want to damage it from the start. If you were using the logic probe on the Colecovision where exactly would you connect the black and red clips.I am looking for specific locations so I connect them to the correct spot. Thanks again for your help.



#30 ChildOfCv OFFLINE  

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Posted Mon Feb 18, 2019 8:22 PM

1764007603.png

Here's where I'd attach them.  Just make sure the red one especially doesn't get pulled around to touch stuff that it shouldn't as you're probing around.



#31 vgcollector OFFLINE  

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Posted Mon Feb 18, 2019 8:45 PM

attachicon.gif1764007603.png

Here's where I'd attach them.  Just make sure the red one especially doesn't get pulled around to touch stuff that it shouldn't as you're probing around.

Great picture. The black clip is attached to the frame of the power switch, but what is the red clip attached to? I appreciate the detailed picture. I just want to make sure I am doing it right.



#32 ChildOfCv OFFLINE  

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Posted Mon Feb 18, 2019 10:33 PM

It's a large choke that the +5V runs through.



#33 vgcollector OFFLINE  

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Posted Tue Feb 19, 2019 6:26 AM

It's a large choke that the +5V runs through.

Ok, thanks. I see what you are connected to now. I couldn't see the tip of clip connected until you told me where it was connecting. Thank you again. I will let you know what I find. I hope to get this done in the next couple of days.



#34 MarcusFrom1982 OFFLINE  

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Posted Tue Feb 19, 2019 10:36 PM

Clean the power supply plug sockets and the plug pins in the back of the colecovision. This can do WONDERS!

#35 vgcollector OFFLINE  

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Posted Sun Feb 24, 2019 5:23 PM

Getting closer to using the probe, but I don't want to damage it from the start. If you were using the logic probe on the Colecovision where exactly would you connect the black and red clips.I am looking for specific locations so I connect them to the correct spot. Thanks again for your help.

Finally got brave and hooked up the logic probe. Now I want to make sure I am numbering the pins correctly. From the top of the chip using U22 as an example. I have 14 pins total. I read that the numbering sequence is in a counter clockwise order. So looking at the top of the chip where it is labeled U22. The pin 1 is on the left goes down the left side 1-7. Then 8 starts from the bottom of the right side of the chip and goes up along the right side 8-14. Am I numbering the pins correctly?



#36 nick3092 OFFLINE  

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Posted Sun Feb 24, 2019 5:37 PM

Finally got brave and hooked up the logic probe. Now I want to make sure I am numbering the pins correctly. From the top of the chip using U22 as an example. I have 14 pins total. I read that the numbering sequence is in a counter clockwise order. So looking at the top of the chip where it is labeled U22. The pin 1 is on the left goes down the left side 1-7. Then 8 starts from the bottom of the right side of the chip and goes up along the right side 8-14. Am I numbering the pins correctly?

Sounds like you are describing it right. Visually it would look something like this (U is the notch)

1 U 14
2     13
3     12
4     11
5     10
6     9
7     8

Edited by nick3092, Sun Feb 24, 2019 5:38 PM.


#37 vgcollector OFFLINE  

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Posted Sun Feb 24, 2019 5:53 PM

Sounds like you are describing it right. Visually it would look something like this (U is the notch)
 

1 U 14
2     13
3     12
4     11
5     10
6     9
7     8

Ok thanks. I thought I had it right, but I wanted to make sure  because if I wasn't I needed to find out now.

 

ChildofCV, I checked all the readings on the chips and they match up with what you had above for chips U22, U8, and U7. I was really hoping one of these would have showed us some failure. What should I check next?

 

I am really learning some new stuff, and thank you to everyone who has responded to this post. Hopefully at the end I will have some kind of procedure that will help anyone who gets the black screen issue when you switch on the Colecovision. I am good at documenting fixes.



#38 ChildOfCv OFFLINE  

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Posted Sun Feb 24, 2019 6:22 PM

So if U22 pin 4 is blinking, that means you have video clock.  You've also checked that the reset circuit is allowing operation and that the other clocks are working.

 

I guess next, we should see if the VDC is alive.  It's a bit more challenging to count it out since it has 40 pins, and because the heat sink prevents you from seeing the pin 1 identifier.  At least, it should have a heat sink.  On mine, the sink fell off and was rattling around inside.  Fortunately the VDC still worked, so I got some double-sided thermal tape and stuck it back on.

 

Anyway, the chip is upside down compared to the others.  Pin 1 is upper right.

 

For signs of life, check pins 1 and 2 for blinking.  In fact, everything from 1-9 ought to blink some.  

10 and 11 only activate when it's writing data to a chip.  So unless a game is in the middle of playing, 10 and 11 are uncertain.  

12 is ground, so should read low.  

13 comes from the CV's address bus and will probably be blinking as a matter of course.  

14 and 15 are select inputs from the CV.  They will be reading high unless it's actually talking to the chip.  

16 goes low whenever vertical retrace happens, but only when the interrupt is enabled by software.  I would expect it to be constant high for this situation.  But if it's blinking, that's acceptable.  

17-24 are the system data bus, so you should see blinking on all of those.  

25-32 will be dependent on VDC reading memory.  I suspect them to be pretty quiet unless a game running.  

33 is the +5 supply and should read high.  

34 is an external reset input and should read high.  

35, 36, and 38 (note that we skip a pin here) are the video signal outputs.  They are analog, so the probe will probably not give you any useful indications from them.  

37 is a clock output.  The CV leaves the pin disconnected, but it ought to be blinking.  

39 is also disconnected but will probably be blinking if you probe it.  

Finally, 40 is the clock input.  We already tested it from the clock generator, but you could check it here at the input just to make sure it didn't get interrupted on the way.

 

If all of that is as described, the VRAM chips are the next suspect.



#39 vgcollector OFFLINE  

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Posted Sun Feb 24, 2019 7:38 PM

So if U22 pin 4 is blinking, that means you have video clock.  You've also checked that the reset circuit is allowing operation and that the other clocks are working.

 

I guess next, we should see if the VDC is alive.  It's a bit more challenging to count it out since it has 40 pins, and because the heat sink prevents you from seeing the pin 1 identifier.  At least, it should have a heat sink.  On mine, the sink fell off and was rattling around inside.  Fortunately the VDC still worked, so I got some double-sided thermal tape and stuck it back on.

 

Anyway, the chip is upside down compared to the others.  Pin 1 is upper right.

 

For signs of life, check pins 1 and 2 for blinking.  In fact, everything from 1-9 ought to blink some.  

10 and 11 only activate when it's writing data to a chip.  So unless a game is in the middle of playing, 10 and 11 are uncertain.  

12 is ground, so should read low.  

13 comes from the CV's address bus and will probably be blinking as a matter of course.  

14 and 15 are select inputs from the CV.  They will be reading high unless it's actually talking to the chip.  

16 goes low whenever vertical retrace happens, but only when the interrupt is enabled by software.  I would expect it to be constant high for this situation.  But if it's blinking, that's acceptable.  

17-24 are the system data bus, so you should see blinking on all of those.  

25-32 will be dependent on VDC reading memory.  I suspect them to be pretty quiet unless a game running.  

33 is the +5 supply and should read high.  

34 is an external reset input and should read high.  

35, 36, and 38 (note that we skip a pin here) are the video signal outputs.  They are analog, so the probe will probably not give you any useful indications from them.  

37 is a clock output.  The CV leaves the pin disconnected, but it ought to be blinking.  

39 is also disconnected but will probably be blinking if you probe it.  

Finally, 40 is the clock input.  We already tested it from the clock generator, but you could check it here at the input just to make sure it didn't get interrupted on the way.

 

If all of that is as described, the VRAM chips are the next suspect.

Ok, here are my findings. Just to clarify I started with pin 1 on the right side of the chip, and then 40 would be in the top left.

For signs of life, check pins 1 and 2 for blinking.  In fact, everything from 1-9 ought to blink some. -1-blinking, 2-low

10 and 11 only activate when it's writing data to a chip.  So unless a game is in the middle of playing, 10 and 11 are uncertain.  -didnt test

12 is ground, so should read low.  -Low

13 comes from the CV's address bus and will probably be blinking as a matter of course.- Low 

14 and 15 are select inputs from the CV.  They will be reading high unless it's actually talking to the chip.- 14- blink, 15- low 

16 goes low whenever vertical retrace happens, but only when the interrupt is enabled by software.  I would expect it to be constant high for this situation.  But if it's blinking, that's acceptable.  - Low

17-24 are the system data bus, so you should see blinking on all of those.17-19 blink, 20-24 blink,  

25-32 will be dependent on VDC reading memory.  I suspect them to be pretty quiet unless a game running-Didn't test.  

33 is the +5 supply and should read high. - Low

34 is an external reset input and should read high.  -Low

35, 36, and 38 (note that we skip a pin here) are the video signal outputs.  They are analog, so the probe will probably not give you any useful indications from them.  -didn't test

37 is a clock output.  The CV leaves the pin disconnected, but it ought to be blinking.  Blinking

39 is also disconnected but will probably be blinking if you probe it.  Blinking

Finally, 40 is the clock input.  We already tested it from the clock generator, but you could check it here at the input just to make sure it didn't get interrupted on the way.-Blink

 

Let me know what you think of these readings. The Pin 33 & 34 were the ones that stood out to me.

Thanks for the quick replies. I am probably done testing for the night, but let me know what direction you would like me to test or re-test.



#40 vgcollector OFFLINE  

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Posted Sun Feb 24, 2019 10:14 PM

Ok, here are my findings. Just to clarify I started with pin 1 on the right side of the chip, and then 40 would be in the top left.

For signs of life, check pins 1 and 2 for blinking.  In fact, everything from 1-9 ought to blink some. -1-blinking, 2-low

10 and 11 only activate when it's writing data to a chip.  So unless a game is in the middle of playing, 10 and 11 are uncertain.  -didnt test

12 is ground, so should read low.  -Low

13 comes from the CV's address bus and will probably be blinking as a matter of course.- Low 

14 and 15 are select inputs from the CV.  They will be reading high unless it's actually talking to the chip.- 14- blink, 15- low 

16 goes low whenever vertical retrace happens, but only when the interrupt is enabled by software.  I would expect it to be constant high for this situation.  But if it's blinking, that's acceptable.  - Low

17-24 are the system data bus, so you should see blinking on all of those.17-19 blink, 20-24 blink,

25-32 will be dependent on VDC reading memory.  I suspect them to be pretty quiet unless a game running-Didn't test.

33 is the +5 supply and should read high. - Low

34 is an external reset input and should read high.  -Low

35, 36, and 38 (note that we skip a pin here) are the video signal outputs.  They are analog, so the probe will probably not give you any useful indications from them.  -didn't test

37 is a clock output.  The CV leaves the pin disconnected, but it ought to be blinking.  Blinking

39 is also disconnected but will probably be blinking if you probe it.  Blinking

Finally, 40 is the clock input.  We already tested it from the clock generator, but you could check it here at the input just to make sure it didn't get interrupted on the way.-Blink

 

Let me know what you think of these readings. The Pin 33 & 34 were the ones that stood out to me.

Thanks for the quick replies. I am probably done testing for the night, but let me know what direction you would like me to test or re-test.

I just wanted to verify I am checking the pins in the right way since this is reversed. Here is my assumptions for the pin locations.

Attached Thumbnails

  • Colecovision pin numbering.JPG


#41 ChildOfCv OFFLINE  

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Posted Sun Feb 24, 2019 10:39 PM

The indentation for that chip is on the right, so by the diagram above, you have the two backwards.  Also, remember that the pins go counter-clockwise.  So pin 1 is upper right, pin 20 is upper left, 21 is lower left, and 40 is lower right.

20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1
+---------------------------------------------------------+
|                                                         |
|                                                        _|
|                                                       {_|
|                                                         |
|                                                         |
+---------------------------------------------------------+
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Edited by ChildOfCv, Sun Feb 24, 2019 10:40 PM.


#42 omf OFFLINE  

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Posted Mon Feb 25, 2019 2:50 AM

33 is the +5 supply and should read high. - Low

the first thing you need to do is get this working

 

sounds like the issue is elseware

 

unlesss the chip is completely fried and internally shorted between ground and +5,  but if that was the case i would think that nothing else would work (the activity readings)


Edited by omf, Mon Feb 25, 2019 2:52 AM.


#43 vgcollector OFFLINE  

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Posted Mon Feb 25, 2019 6:12 AM

 

The indentation for that chip is on the right, so by the diagram above, you have the two backwards.  Also, remember that the pins go counter-clockwise.  So pin 1 is upper right, pin 20 is upper left, 21 is lower left, and 40 is lower right.

20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1
+---------------------------------------------------------+
|                                                         |
|                                                        _|
|                                                       {_|
|                                                         |
|                                                         |
+---------------------------------------------------------+
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Ok, sorry, I misunderstood what you were saying about the pin numbering being the opposite on this chip. I will retest tonight and post my readings. FYI, I am doing all these tests with power on, a cartridge inserted, and 1 controller plugged in port 1. Is that how I should be testing?



#44 ChildOfCv OFFLINE  

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Posted Mon Feb 25, 2019 2:33 PM

Yes, the testing conditions ought to work.

 

But now that you've reminded me, I think I did jump the gun.  For review:

 

You've tested the voltages in the system already:  +5, -5, and +12V are correct.

 

Atari expansion shows video and audio.  So the RF modulator works.

 

No sound or video from Frogger.  This suggests that the problem comes BEFORE the video controller.  ROM, RAM, CPU, or glue logic.

 

 

You could verify that the VDC is alive using the pin listings, but let's also turn attention to U6, which is just under the VDC on the right side.  This maps outputs to I/O ports.  VDC and sound are both I/O ports, as are the game controllers.

 8   7   6   5   4   3   2   1
+-----------------------------+
|                            _|
|                           (_|
|                             |
+-----------------------------+
 9  10  11  12  13  14  15  16

1 is for port read vs write.  If the CPU is alive (and it probably is), then you should see this blinking.

2-3 and 6 are address bus lines and should also be blinking.

4 is the I/O request line and should be blinking.

5 is for overriding the I/O ports.  It should be low.

7 selects one of the controller ports.  It will be high until the program starts looking for input, then blinking.  So, option screen or later (but typically not while doing a death pause or whatnot)

8 is ground, so low

9 selects the sound chip.  If you have Frogger in, it ought to be blinking all the time.

10 is not connected.  Should be high.

11 selects one of the controller read modes (joystick, I think... never can keep them straight without looking it up).  Should be blinking if the game is polling for input.  Well, technically, software can do what it wants... it could, for instance, leave the controller in one mode or the other if it doesn't care about the other input type at the moment.  But the ROM routine polls both in the same call, so if the game uses it, you'll get the blinking.

12 is VDC read.  For Frogger, this should be happening from the time you turn the system on.  So, blinking.

13 is VDC write.  Blinking.

14 is not connected and ought to be high.

15 is the other controller read mode.  So discussion about 11 applies.

16 is +5V.  So high.


Edited by ChildOfCv, Mon Feb 25, 2019 2:34 PM.


#45 vgcollector OFFLINE  

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Posted Mon Feb 25, 2019 2:43 PM

Hi, thanks for the additional conditions to check so we are both on the same page. I will test all of these conditions on the Colecovision I am working on. I will test these and then test the pins on VDC again. It will be later this afternoon as I am not home right now.

Thanks



#46 vgcollector OFFLINE  

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Posted Mon Feb 25, 2019 5:55 PM

Hi, thanks for the additional conditions to check so we are both on the same page. I will test all of these conditions on the Colecovision I am working on. I will test these and then test the pins on VDC again. It will be later this afternoon as I am not home right now.

Thanks

Ok, here is my latest testing results. I verified power voltages are correct. I plugged in Frogger, no sound. I plugged in Atari Expansion Module, got picture and sound.

 

With Frogger plugged in cart slot

U9 Results- Exception indicates does not match your expected results

Pins 1-8 – Blink

Pin 9- High- Exception

Pins 10 & 11- didn’t test

Pin 12 – Low

Pin 13 – Blinking

Ping 14 & 15 –High

Pin 16 – High- Exception

Pin 17-20, 22-24 – Blinking

Pin 21 – Low- Exception

Pins 25-32 – Didn’t Test

Pin 33 – High

Pin 34 – High

Pins 35, 36, & 38 – Didn’t test

Pin 37 – Blinking

Pin 39 – Low- Exception

Pin 40 – Blinking

 

U6

Pin 1 – High

Pins 2-3, 6- Blinking

Pin 4 – High-Exception

Pin 5 – Low

Pin 6,7 – Didn’t test

Pin 8 – Low

Pin 9 – High – with Frogger plugged in- Exception

Pin 10 – High

Pin 11 – High- Exception

Pin 12 – High- Exception

Pin 13 –High- Exception

Pin 14 – High

Pin 15- High

Pin 16 - High

 

FYI, I saw in the CV technical manual that if you have a black screen after playing for a while, check the polarity of C106 which is a 10 uf tantalum. How do you check polarity. This may have nothing to do with the issue but just wanted to tell you I ran across it. It says to replace it if the polarity is wrong.

 

As always I appreciate the Help!!



#47 ChildOfCv OFFLINE  

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Posted Mon Feb 25, 2019 7:14 PM

Ok, here is my latest testing results. I verified power voltages are correct. I plugged in Frogger, no sound. I plugged in Atari Expansion Module, got picture and sound.

 

With Frogger plugged in cart slot

U9 Results- Exception indicates does not match your expected results

Pin 9- High- Exception   Interesting.  Well, according to the VDC manual, on first reset, it clear the mode registers.  Mode register 2, if zero, thinks it only has 4K memory.  So I guess it's acceptable for this pin to be unused if the VDC has never been configured at all.  Since other signs show that we aren't being programmed, I'm okay with this result.

Pin 16 – High- Exception  This is also consistent with not being programmed yet.  Until you enable interrupts, the pin will stay high.

Pin 21 – Low- Exception  This one is very odd.  It's one of the CV's data bus lines and should definitely see activity.  This is an input though, so this does not indicate a problem with the VDC itself.

Pin 39 – Low- Exception  This isn't what I expected since it's part of the oscillator circuit.  But with everything else apparently working, I'll just shrug and say "ok".  In other designs where the VDC has its own crystal, it gets connected between pins 39 and 40.  In this one we feed pin 40 with a signal.  But I guess for that design, pin 39 is unaffected.

U6

Pin 1 – High  This is bad.  It means the CPU isn't talking to the I/O at all, not even for memory.  When the processor is writing either to I/O or memory, this line should go low.

Pin 4 – High-Exception  This also indicates that the CPU isn't making any attempts at I/O.

Pin 9 – High – with Frogger plugged in- Exception  Not surprising about the outputs:  With no request to any I/O port, there will be no outputs.


FYI, I saw in the CV technical manual that if you have a black screen after playing for a while, check the polarity of C106 which is a 10 uf tantalum. How do you check polarity. This may have nothing to do with the issue but just wanted to tell you I ran across it. It says to replace it if the polarity is wrong.  By itself, this doesn't make sense to me.  I'll have to look at it, but at present I don't think it's the issue.  This capacitor filters the power to the VDC.  At the moment, that appears to be okay.

 

As always I appreciate the Help!!

With a dead data bit, I am beginning to suspect memory chips.  The CPU only does what it's told, and without good memory it's going to be told some really funky stuff.  Could you give me a reading on U3 and U4?  I'd offer my expectations, but I need to be somewhere.  BBL.



#48 vgcollector OFFLINE  

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Posted Mon Feb 25, 2019 8:42 PM

With a dead data bit, I am beginning to suspect memory chips.  The CPU only does what it's told, and without good memory it's going to be told some really funky stuff.  Could you give me a reading on U3 and U4?  I'd offer my expectations, but I need to be somewhere.  BBL.

I tested U3 and U4. I did want to let you know that on this one I got some different readings and tones. I will try to describe what I saw on the probe as well as I can.

 

U3

1-low/high lights lit blinking low tone

2- low/high lights lit blinking low tone

3- low/high lights lit blinking low tone

4- low/hgih lights lit blinking high tone

5-low/high lights lit blinking low tone

6- low/high lights lit blinking high tone

7- low/high lights lit blinking high tone

8- low/high lights lit blinking high tone

9- Low

10-High

11-Low Blinking

12- Low Blinking

13- Low Blinking

14- Low Blinking

15- Low Blinking

16- Low Blinking

17- Low

18 - High

 

U4

1- Low/High lights lit Low tone

2- Low/High lights lit Low tone

3 - Low light lit Blinking

4- low/high lights lit blinking high tone

5- low/high lights lit blinking high tone

6- low/high lights lit blinking high tone

7- low/high lights lit blinking high tone

8- High

9- Low

10-High

11- Low lit Blinking

12- Low lit Blinking

13- Low lit Blinking

14- Low lit Blinking

15- Low/ High lit Blinking

16- Low/High lit Blinking

17- Low

18- High

 

I hope this is clear to you. I don't know if you have a spreadsheet with all these readings, but I was thinking about doing the readings on a working Colecovision and then comparing it to what we are finding with this broken one. I think a spreadsheet might be helpful in organizing all of this. Thanks



#49 ChildOfCv OFFLINE  

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Posted Mon Feb 25, 2019 10:57 PM

Hmmm... there are a couple of things off here.  First of all, pin 8 is electrically connected to both chips.  So unless there's a bad trace on the motherboard, you should not see any difference between reading the chips.  Also, you show all data lines working here, which makes it hard to believe one would be dead on the TI chip.  Here's a diagram of the chips to help:

Gd CS A2 A1 A0 A3 A4 A5 A6
 9  8  7  6  5  4  3  2  1
+-------------------------+
|                        _|
|                       (_|
|                         |
+-------------------------+
10 11 12 13 14 15 16 17 18
WR D3 D2 D1 D0 A9 A8 A7 +5

Now, it isn't impossible to see the above happen... if the board is cracked and the traces are broken in some area.  But for now I'd like you to double-check the readings.  And if you do see blinking on all of the D lines above on both chips, re-check pin 21 on the VDC.  It should be connected to pin 14 on the lower memory chip.

 

Screen Shot 2019-02-25 at 9.56.00 PM.png

Screen Shot 2019-02-25 at 9.56.46 PM.png



#50 vgcollector OFFLINE  

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Posted Tue Feb 26, 2019 6:14 AM

Hmmm... there are a couple of things off here.  First of all, pin 8 is electrically connected to both chips.  So unless there's a bad trace on the motherboard, you should not see any difference between reading the chips.  Also, you show all data lines working here, which makes it hard to believe one would be dead on the TI chip.  Here's a diagram of the chips to help:

Gd CS A2 A1 A0 A3 A4 A5 A6
 9  8  7  6  5  4  3  2  1
+-------------------------+
|                        _|
|                       (_|
|                         |
+-------------------------+
10 11 12 13 14 15 16 17 18
WR D3 D2 D1 D0 A9 A8 A7 +5

Now, it isn't impossible to see the above happen... if the board is cracked and the traces are broken in some area.  But for now I'd like you to double-check the readings.  And if you do see blinking on all of the D lines above on both chips, re-check pin 21 on the VDC.  It should be connected to pin 14 on the lower memory chip.

 

attachicon.gifScreen Shot 2019-02-25 at 9.56.00 PM.png

attachicon.gifScreen Shot 2019-02-25 at 9.56.46 PM.png

Thanks for the pictures. That helps to see how they are connected. I will redo these readings tonight.






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