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Hi folks,
For 7854 owners who have been suffering from the ROM Rot problem with their EPROMS - I've developed a drop-in replacement for the MCM68766 EPROM that you may find interesting. A short video appears here. If it's of interest to a sizeable number of people I can make it available on ePray. The board can be programmed on any MCM68766 programmer and replaces the original with no other mods required.
Best - Ram
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Nice. Is the schematic public?
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On Tue, Apr 5, 2022 at 06:31 AM, Ram wrote:
For 7854 owners who have been suffering from the ROM Rot problem with their
EPROMS
A few years ago, our member Holger Lübben designed a replacement ROM card using commonly available components. He had complete sets and kits available. See this thread: /g/TekScopes/topic/76166880#170558The board contains the complete operating software and also supports the diagnostic mode, to be selected by an on-board switch.. I'm lucky enough to have one and it works very well. AFAIK, it's out of stock and he does not intend to produce more. Raymond
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The MCM68766 can always be replaced by a 2764 using a 28 dip socket to 24 dip header.? I don't have a 7854 and didn't look up the specs, but need to check the access time.? I built a few adapters for the Commodore 64 computer and 1541 disk drive.? The rom in the 1541 was close to the TO3 voltage regulator and the heat seemed to cause failures.? Replacements worked great.? If details are needed and you can't find it on the internet, I can look through my junk for the method I used.? I also copied Commodore? roms to MCM68766.??
Carl Hallberg (W9CJH)
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On Tuesday, April 5, 2022, 05:58:21 PM CDT, Raymond Domp Frank <hewpatek@...> wrote: On Tue, Apr? 5, 2022 at 06:31 AM, Ram wrote:
For 7854 owners who have been suffering from the ROM Rot problem with their
EPROMS
A few years ago, our member Holger Lübben designed a replacement ROM card using commonly available components. He had complete sets and kits available. See this thread: /g/TekScopes/topic/76166880#170558The board contains the complete operating software and also supports the diagnostic mode, to be selected by an on-board switch.. I'm lucky enough to have one and it works very well. AFAIK, it's out of stock and he does not intend to produce more. Raymond
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On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to 24 dip
header.? I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin ROMs are mounted end-to-end lengthwise with only 0.2" in between, which doesn't allow for the longer 28-pin 2764's. on standard converting headers. The two rows of two each that make up the total of four ROMs are 0.3" apart. There would be enough space if one built a flat plug-in piggy-back PCB and mounted the replacement EPROMs without sockets. Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one 7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't suffer from "ROM-rot". BTW, the board contains extra hardware that allows patching of data in address ranges read from the ROMs, probably because it was considered too slow and expensive to run new masks if a change was made. Raymond
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Brian - The schematic is quite simple and I'd be happy to share it in reply to a PM.
Raymond - thanks for correcting me on the ROM rot in mask ROMs.
Best - Ram
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On Wed, Apr 6, 2022 at 06:06 AM, Ram wrote:
Raymond - thanks for correcting me on the ROM rot in mask ROMs.
Hi RAM, I realize that I didn't even mention your solution/device, which I think is very elegant. Programming the device may be a complication for some though. Can a simple device like the popular TLS-866 (different versions), possibly with some sort of adapter, be made to do the job? The elevated programming voltage for UV-erasable EPROMs (not available on recent versions of the TLS-866) won't be needed of course. Raymond
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The extra hardware for patching consisted of an FPLA (Field-Programmable Logic Array) and a PROM. The FPLA monitored the address bus, and on certain ranges it rerouted Chip Select from the mask roms to the patch rom. From the processor’s point of view, this replaced a couple of instructions with a jump that led to replacement code in the PROM, which did its thing then jumped back to the mask ROM. This scheme was used in 1980 in the 4024/4025/4027 terminals made by the Information Display Division at the Wilsonville plant. Later models used EPROMs, 2732 and up if I recall correctly. Dave Wise IDD 1980-1995 From: [email protected] < [email protected]> On Behalf Of Raymond Domp Frank via groups.io Sent: Tuesday, April 05, 2022 8:08 PM To: [email protected]Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766 EPROM On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to 24 dip
header. I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin ROMs are mounted end-to-end lengthwise with only 0.2" in between, which doesn't allow for the longer 28-pin 2764's. on standard converting headers. The two rows of two each that make up the total of four ROMs are 0.3" apart. There would be enough space if one built a flat plug-in piggy-back PCB and mounted the replacement EPROMs without sockets. Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one 7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't suffer from "ROM-rot". BTW, the board contains extra hardware that allows patching of data in address ranges read from the ROMs, probably because it was considered too slow and expensive to run new masks if a change was made. Raymond
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I have a whole tube of mcm68764L eproms.? If these can replace the proms, I will mail 5 to someone who can and wants to program them.? I cannot find data sheet on Google, so don't know specs.? One of the eproms of the 5 I did attempt to program and may or may not have been damaged.? That is why 5 of them.? I also have mcm68766,? but may need them (or some) in the future for Tek, HP?? Will mail to contiguous United States. You pay postage.? I am looking for 2 Toshiba TA7761P.? The description on internet is wrong, so never attempted to purchase.? Used in radio control.??
By the way Raymond, the roms in the Commodore 64 were also Mostek.? Maybe why some of the failures.
Carl Hallberg (W9CJH)
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Show quoted text
On Wednesday, April 6, 2022, 10:33:35 AM CDT, Dave Wise <david_wise@...> wrote: The extra hardware for patching consisted of an FPLA (Field-Programmable Logic Array) and a PROM.? The FPLA monitored the address bus, and on certain ranges it rerouted Chip Select from the mask roms to the patch rom.? From the processor’s point of view, this replaced a couple of instructions with a jump that led to replacement code in the PROM, which did its thing then jumped back to the mask ROM. This scheme was used in 1980 in the 4024/4025/4027 terminals made by the Information Display Division at the Wilsonville plant.? Later models used EPROMs, 2732 and up if I recall correctly. Dave Wise IDD 1980-1995 From: [email protected] < [email protected]> On Behalf Of Raymond Domp Frank via groups.io Sent: Tuesday, April 05, 2022 8:08 PM To: [email protected]Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766 EPROM On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to 24 dip
header.? I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin ROMs are mounted end-to-end lengthwise with only 0.2" in between, which doesn't allow for the longer 28-pin 2764's. on standard converting headers. The two rows of two each that make up the total of four ROMs are 0.3" apart. There would be enough space if one built a flat plug-in piggy-back PCB and mounted the replacement EPROMs without sockets. Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one 7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't suffer from "ROM-rot". BTW, the board contains extra hardware that allows patching of data in address ranges read from the ROMs, probably because it was considered too slow and expensive to run new masks if a change was made. Raymond
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On my mini-board I have brought out the three pins required for programming the onboard EEPROM into a header provision so you can directly program the EEPROM without any high voltage programmers.
-Ram
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On Wed, Apr 6, 2022 at 05:01 AM, Raymond Domp Frank wrote:
Hi RAM,
I realize that I didn't even mention your solution/device, which I think is
very elegant. Programming the device may be a complication for some though.
Can a simple device like the popular TLS-866 (different versions), possibly
with some sort of adapter, be made to do the job? The elevated programming
voltage for UV-erasable EPROMs (not available on recent versions of the
TLS-866) won't be needed of course.
|
The Motorola ROMs may be better than the Mostek mask ROMs but they are not immune to ROM rot. The Motorola ROMs in my 7854 went bad.
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Sorry about an error in the flat pack chip I'm looking for.? I wrote TA7761P and should be TA7761F.? Off topic.
Carl Hallberg (W9CJH)
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Show quoted text
On Wednesday, April 6, 2022, 12:02:35 PM CDT, Carl Hallberg via groups.io <n9ess@...> wrote: I have a whole tube of mcm68764L eproms.? If these can replace the proms, I will mail 5 to someone who can and wants to program them.? I cannot find data sheet on Google, so don't know specs.? One of the eproms of the 5 I did attempt to program and may or may not have been damaged.? That is why 5 of them.? I also have mcm68766,? but may need them (or some) in the future for Tek, HP?? Will mail to contiguous United States. You pay postage.? I am looking for 2 Toshiba TA7761P.? The description on internet is wrong, so never attempted to purchase.? Used in radio control.?? By the way Raymond, the roms in the Commodore 64 were also Mostek.? Maybe why some of the failures. Carl Hallberg (W9CJH) On Wednesday, April 6, 2022, 10:33:35 AM CDT, Dave Wise <david_wise@...> wrote: The extra hardware for patching consisted of an FPLA (Field-Programmable Logic Array) and a PROM.? The FPLA monitored the address bus, and on certain ranges it rerouted Chip Select from the mask roms to the patch rom.? From the processor’s point of view, this replaced a couple of instructions with a jump that led to replacement code in the PROM, which did its thing then jumped back to the mask ROM. This scheme was used in 1980 in the 4024/4025/4027 terminals made by the Information Display Division at the Wilsonville plant.? Later models used EPROMs, 2732 and up if I recall correctly. Dave Wise IDD 1980-1995 From: [email protected] < [email protected]> On Behalf Of Raymond Domp Frank via groups.io Sent: Tuesday, April 05, 2022 8:08 PM To: [email protected]Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766 EPROM On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to 24 dip
header.? I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin ROMs are mounted end-to-end lengthwise with only 0.2" in between, which doesn't allow for the longer 28-pin 2764's. on standard converting headers. The two rows of two each that make up the total of four ROMs are 0.3" apart. There would be enough space if one built a flat plug-in piggy-back PCB and mounted the replacement EPROMs without sockets. Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one 7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't suffer from "ROM-rot". BTW, the board contains extra hardware that allows patching of data in address ranges read from the ROMs, probably because it was considered too slow and expensive to run new masks if a change was made. Raymond
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Commodore used MOS Technology chips, since they owned the company. On Wed, Apr 6, 2022 at 5:46 PM Carl Hallberg via groups.io <n9ess= [email protected]> wrote: Sorry about an error in the flat pack chip I'm looking for. I wrote
TA7761P and should be TA7761F. Off topic.
Carl Hallberg (W9CJH)
On Wednesday, April 6, 2022, 12:02:35 PM CDT, Carl Hallberg via groups.io
<n9ess@...> wrote:
I have a whole tube of mcm68764L eproms. If these can replace the proms,
I will mail 5 to someone who can and wants to program them. I cannot find
data sheet on Google, so don't know specs. One of the eproms of the 5 I
did attempt to program and may or may not have been damaged. That is why 5
of them. I also have mcm68766, but may need them (or some) in the future
for Tek, HP? Will mail to contiguous United States. You pay postage. I am
looking for 2 Toshiba TA7761P. The description on internet is wrong, so
never attempted to purchase. Used in radio control.
By the way Raymond, the roms in the Commodore 64 were also Mostek. Maybe
why some of the failures.
Carl Hallberg (W9CJH)
On Wednesday, April 6, 2022, 10:33:35 AM CDT, Dave Wise <
david_wise@...> wrote:
The extra hardware for patching consisted of an FPLA (Field-Programmable
Logic Array) and a PROM. The FPLA monitored the address bus, and on
certain ranges it rerouted Chip Select from the mask roms to the patch
rom. From the processor’s point of view, this replaced a couple of
instructions with a jump that led to replacement code in the PROM, which
did its thing then jumped back to the mask ROM.
This scheme was used in 1980 in the 4024/4025/4027 terminals made by the
Information Display Division at the Wilsonville plant. Later models used
EPROMs, 2732 and up if I recall correctly.
Dave Wise
IDD 1980-1995
From: [email protected] <[email protected]> On Behalf Of Raymond Domp
Frank via groups.io
Sent: Tuesday, April 05, 2022 8:08 PM
To: [email protected]
Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766
EPROM
On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to
24 dip
header. I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin
ROMs are mounted end-to-end lengthwise with only 0.2" in between, which
doesn't allow for the longer 28-pin 2764's. on standard converting headers.
The two rows of two each that make up the total of four ROMs are 0.3"
apart. There would be enough space if one built a flat plug-in piggy-back
PCB and mounted the replacement EPROMs without sockets.
Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one
7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by
Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't
suffer from "ROM-rot". BTW, the board contains extra hardware that allows
patching of data in address ranges read from the ROMs, probably because it
was considered too slow and expensive to run new masks if a change was made.
Raymond
|
I wonder if any lawsuits over the similarity in names.? MOSTEK? MOS TEK? verses MOS Technology.? I remember Commodore had very fast turnaround when upgrading design on their color chip because they bought a semiconductor company.? I didn't follow the details.? A company I worked for had a threat of lawsuit because of similar names.
Carl Hallberg
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Show quoted text
On Wednesday, April 6, 2022, 06:10:19 PM CDT, Michael A. Terrell <terrell.michael.a@...> wrote: Commodore used MOS Technology chips, since they owned the company. On Wed, Apr 6, 2022 at 5:46 PM Carl Hallberg via groups.io <n9ess= [email protected]> wrote: Sorry about an error in the flat pack chip I'm looking for.? I wrote
TA7761P and should be TA7761F.? Off topic.
Carl Hallberg (W9CJH)
On Wednesday, April 6, 2022, 12:02:35 PM CDT, Carl Hallberg via groups.io
<n9ess@...> wrote:
I have a whole tube of mcm68764L eproms.? If these can replace the proms,
I will mail 5 to someone who can and wants to program them.? I cannot find
data sheet on Google, so don't know specs.? One of the eproms of the 5 I
did attempt to program and may or may not have been damaged.? That is why 5
of them.? I also have mcm68766,? but may need them (or some) in the future
for Tek, HP?? Will mail to contiguous United States. You pay postage.? I am
looking for 2 Toshiba TA7761P.? The description on internet is wrong, so
never attempted to purchase.? Used in radio control.
By the way Raymond, the roms in the Commodore 64 were also Mostek.? Maybe
why some of the failures.
Carl Hallberg (W9CJH)
On Wednesday, April 6, 2022, 10:33:35 AM CDT, Dave Wise <
david_wise@...> wrote:
The extra hardware for patching consisted of an FPLA (Field-Programmable
Logic Array) and a PROM.? The FPLA monitored the address bus, and on
certain ranges it rerouted Chip Select from the mask roms to the patch
rom.? From the processor’s point of view, this replaced a couple of
instructions with a jump that led to replacement code in the PROM, which
did its thing then jumped back to the mask ROM.
This scheme was used in 1980 in the 4024/4025/4027 terminals made by the
Information Display Division at the Wilsonville plant.? Later models used
EPROMs, 2732 and up if I recall correctly.
Dave Wise
IDD 1980-1995
From: [email protected] <[email protected]> On Behalf Of Raymond Domp
Frank via groups.io
Sent: Tuesday, April 05, 2022 8:08 PM
To: [email protected]
Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766
EPROM
On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to
24 dip
header.? I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin
ROMs are mounted end-to-end lengthwise with only 0.2" in between, which
doesn't allow for the longer 28-pin 2764's. on standard converting headers.
The two rows of two each that make up the total of four ROMs are 0.3"
apart. There would be enough space if one built a flat plug-in piggy-back
PCB and mounted the replacement EPROMs without sockets.
Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one
7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by
Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't
suffer from "ROM-rot". BTW, the board contains extra hardware that allows
patching of data in address ranges read from the ROMs, probably because it
was considered too slow and expensive to run new masks if a change was made.
Raymond
|
Brian Cockburn
Raymond Domp Frank
Michael A. Terrell