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Is my Tek 468 beyond repair? Trap and Kernel test procedure


Heitor Lima
 

Hi group

I have 2 TEK 468 with problems in digital circuits.
First I would like to inform the group that I never worked with the 8085 microprocessor.
In the page 5.36 of TEK 468 Service Manual, to initiate Trap test we must to momentary unplug P262 and reconnect it . Microprocessor will be interrupted and the Trap Test routine will begin.

My question is, how to know if the routine was performed correctly? I have a 16 channels logic analyzer
and I can record the signature for the whole routine. However, I don't know how to check if it
was performed correctly. Could you ot somebody tell me how to check?

The same applies to the Kernel Test. How to check if the routine was fully complied with by the microprocessor?

I would like to have a step-by-step of the trap and Kernel routines to check if the routine was done correctly.
The same applies to the Kernel Test. How to check if the routine was fully complied with by the microprocessor?

Many thanks in advance

Heitor Lima ( From Rio de Janeiro - Brazil )


Harvey White
 

The 8085 has certain address locations it goes to under certain hardware conditions.  (without me looking them up, it's in the data sheet), there's one for power on reset, the hardware traps (rst 7.5, etc), interrupts and so on.

If you monitor the address lines on the processor (fortunately, 16 of them), then (for example) when the reset line goes active, the processor should show that the address lines go to zero (IIRC) and start to execute there.  In the 8085, you don't have vectors (the processor doesn't fetch and address from location 0, then use that to show where to execute (as in the 6800 or the 6500 series), but starts executing at that location.  Thus, the location typically contains a jump instruction which goes to actual code.

once you see that the location is being jumped to, you may be able to use the higher bit of the address to monitor the triggering event if you wish.

For an 8 bit microprocessor, a 32 bit is more of a minimum requirement, with 16 address, 8 data, and 8 other signals (ALE, R/W, etc).

Still, you could take the highest 4 bits of the address, run them through a 74LS20, then again to invert the answer, and that would give you some indication of the address if you start to trace further.

Harvey

On 9/17/2020 11:34 PM, Heitor Lima via groups.io wrote:
Hi group

I have 2 TEK 468 with problems in digital circuits.
First I would like to inform the group that I never worked with the 8085 microprocessor.
In the page 5.36 of TEK 468 Service Manual, to initiate Trap test we must to momentary unplug P262 and reconnect it . Microprocessor will be interrupted and the Trap Test routine will begin.

My question is, how to know if the routine was performed correctly? I have a 16 channels logic analyzer
and I can record the signature for the whole routine. However, I don't know how to check if it
was performed correctly. Could you ot somebody tell me how to check?

The same applies to the Kernel Test. How to check if the routine was fully complied with by the microprocessor?

I would like to have a step-by-step of the trap and Kernel routines to check if the routine was done correctly.
The same applies to the Kernel Test. How to check if the routine was fully complied with by the microprocessor?

Many thanks in advance

Heitor Lima ( From Rio de Janeiro - Brazil )





tgerbic
 

Heitor,

What are the symptoms of the two scopes and what have you already identified as problems? Perhaps that would help us figure out ways we can help you. Please keep the symptoms of each scope completely separate in your posts so we don't get them confused.

Regards
Tony


Heitor Lima
 

Hi Tony.
First I want to thank you for your kindness in answering me. Both scopes show code 3000 in the POST. I have the service manual. Reading pags 5.36 and 5.37 of the manual, they tell you to check if the trap test and kernel test routines were successful. However, the manual does not inform how each routine is checked. So I put my questions to the group.
I thank you and any other member of the group if you can help me.

Regards

Heitor Lima

PS: The serial numbers are : B010194 and 301977

On Saturday, September 19, 2020, 02:52:43 AM GMT-3, tgerbic <tgerbic@...> wrote:

Heitor,

What are the symptoms of the two scopes and what have you already identified as problems?  Perhaps that would help us figure out ways we can help you. Please keep the symptoms of each scope completely separate in your posts so we don't get them confused.

Regards
Tony


tgerbic
 

Heitor,
POST 3000 indicates that the acquisition RAM has failures. The fact that the testing took place indicates the processor, address bus, data bus and ROM should be ok. The next step would be to use the Service ROM to run some tests, especially on the acquisition RAM. No one seems to be able to product a copy of the service RAM so using the manual's troubleshooting by Service ROM is not going to work. Additionally the manual is focused on using a signature analyzer for much of the testing. Most people don't have one, and I assume you don't either. They were popular back in the 80s but you don't see them today. So, I think the way forward is to use a more general troubleshooting process.

Acquisition RAM is on the A18 board so I suggest you start on the "Partial A18 Memory Board Schematic" ACQUISITION MEMORY<14>. The upper right shows the RAM and the address/data decoders. I would start looking there. Perhaps focus your logic analyzer on one of the chips and see where the test stops when the POST 3000 comes up. Could be a bad RAM chip(s). Since both scopes show a POST 3000 error, it could be the RAMs going bad. I would find it hard to believe you would have identical logic failures on both scopes.

I assume you have checked the digital supply voltages, especially for high ripple voltage. There are two +5V power supply systems, one for the microprocessor section at the back of the scope and a second one on the A15 board which powers digital logic in the rest of the scope. Make sure you rock any ICs that are in sockets to make sure they are making contact in the crummy TI sockets. I would avoid touching the A/D converter chip as it is big and if you break it, it might be very hard to find a replacement.

In any case this should get you started.

Regards
Tony


Heitor Lima
 

Hi Tony
Thank you very much for your guidance.
I have been looking for an image of SERVICE ROM for about 5 years without success. It is unbelievable that nobody in the group has this file. After all, TEK 468 was very popular in the world. I have the image files for the 2 ROM's but unfortunately I don't have the image file for the SERVICE ROM.
All power supply are OK with voltages according to the specifications in the manual. The ripples are also OK.
I'll start with where you suggested.

Regards

Heitor

On Monday, September 21, 2020, 02:02:39 AM GMT-3, tgerbic <tgerbic@...> wrote:

Heitor,
POST 3000 indicates that the acquisition RAM has failures.  The fact that the testing took place indicates the processor, address bus, data bus and ROM should be ok.  The next step would be to use the Service ROM to run some tests, especially on the acquisition RAM. No one seems to be able to product a copy of the service RAM so using the manual's troubleshooting by Service ROM is not going to work.  Additionally the manual is focused on using a signature analyzer for much of the testing.  Most people don't have one, and I assume you don't either.  They were popular back in the 80s but you don't see them today. So, I think the way forward is to use a more general troubleshooting process.

Acquisition RAM is on the A18 board so I suggest you start on the "Partial A18 Memory Board Schematic" ACQUISITION MEMORY<14>. The upper right shows the RAM and the address/data decoders. I would start looking there. Perhaps focus your logic analyzer on one of the chips and see where the test stops when the POST 3000 comes up.  Could be a bad RAM chip(s).  Since both scopes show a POST 3000 error, it could be the RAMs going bad.  I would find it hard to believe you would have identical logic failures on both scopes.

I assume you have checked the digital supply voltages, especially for high ripple voltage.  There are two +5V power supply systems, one for the microprocessor section at the back of the scope and a second one on the A15 board which powers digital logic in the rest of the scope.  Make sure you rock any ICs that are in sockets to make sure they are making contact in the crummy TI sockets.  I would avoid touching the A/D converter chip as it is big and if you break it, it might be very hard to find a replacement.

In any case this should get you started.

Regards
Tony