Doing this backwards...CoCo I restoration

[clh333]

My thanks to posters on the previous thread (below) for their advice, but rather than bump it I am starting this thread anew.

 

 

A few years ago I obtained a Color Computer Disk Drive from an eBay seller.  I thought it might be adaptable for use with a TRS-80 Model III or 4.  I found (after cleaning and replacing a few capacitors) it could be powered on but no activity light showed.  After learning more about it I acquired the floppy disk controller cartridge and cable last year.  After learning more about the controller I found that the (early) controllers depended on +12VDC and that was only available on the CoCo I.  So I bought one a few weeks ago: Model 26-3004, serial number 42063.  It arrived damaged, as the seller had skimped on packaging, and I had to break the seal and open the case to look for damage.  The damage was repairable - the case cracked below the transformer but I was able to glue it together, and I took inventory and some pictures before reassembling and testing with power on.  To my relief I had an operating computer.  Now what?

 

I plugged in the FDC, no drive attached, and turned on the computer.  I did not see any mention of Extended Color Basic as expected: instead the display read Color Basic 1.1 / Ready.  I took the controller apart, unseated & reseated all the ICs and cleaned all the edge connectors and tried again, no change in the display.  Next I tried powering up with the drive attached: nada.  I just learned that I need the Extended Color Basic ROM in the empty socket next to the Basic 1.1 ROM in order to operate the disk drive.  I have an EEPROM burner but I would like to find the proper EEPROM and a copy of the ROM contents so I can upgrade the ROM to Extended.  Can anyone suggest a source, or must I purchase an adapter and someone's pre-flashed ROM?

 

The RAM consists of 8 MCM4116BP2, which would make this a 16K machine.  I would like to upgrade the memory and I understand it is possible to extend it to 64k.  I also understand the procedure for doing so is specific to the model and I would like to ask for advice on where to find materials and instructions for doing so.

 

Finally, the video from the unit is being output to the RF input of a Sony VHF tape player and out its line out to a Commodore 1024 monitor.  Let's just say the display could be better.  Are there options for improving the video?  Bypassing the RF modulator?

 

Thanks for your suggestions,

-CH-

 

 

[+hloberg]

here's a do-it-youself composite for the coco 1 http://www.cocopedia.com/wiki/index.php/CoCo-1_composite_video . I haven't tried it for the coco 1 but know folks who had success with similar for coco 2. & https://hackaday.io/project/7613-coco-1-composite-video-output

 

also if you want VGA http://cocovga.com/

I know the guy who sells and creates these through this website. VERY helpful dude. Drop him an email and he can hook you up with a whole lots of coco stuff and information.

[MrDave]

I can fix up up with a adapter board for tge eeprom

[clh333]

Thank you hloberg for these suggestions; I sent an email to cocovga but will investigate the composite option first.

-CH-

[clh333]

MrDave, Thank you for your offer.  If worst comes to worst I'll follow that lead.  I do have an EPROM burner however and have used it to burn ROMs for my IBM 5170, for example.  I also found the ROM file for Extended Color BASIC on the Tandy Archive, so I think I am 2/3 of the way to creating the missing ROM on a 24-pin EEPROM.  The remaining question is WHICH one agrees with the TRS design.  Can anyone suggest a suitable candidate?

 

Thank you for your suggestions,

-CH-

[MrDave]

Not all eprom burners can do the 24 pin ones..thats  why i cam up with this board design.. whatever is the latest extended basic is good..i think its 1.3..  then you can use disk plus other features in basic..these bare adapter boards are only 1$ 

[MrDave]

This is what the adapter looks like with socket..

[clh333]

Okay, the trouble with posting when you're half-asleep is that your editing facilities are half-asleep as well.  For the record, that's a Sony VHS recorder and a Commodore 1084 monitor mentioned in the OP.  Thank you for ignoring my errors.

 

I found the MCM68766C35 is the wide-body version of the 2764 EEPROM; I have some on order.  Also on order are a couple of Hitachi 6309 CPUs which should be a drop-in replacement.  The cocovga adapter will have to wait until I get these other issues resolved.  I still want to see what I can do to upgrade the memory.  I believe this is a Revision E board.

 

Any suggestions?  Thanks,

-CH-

 

 

 

[MrDave]

3 hours ago, clh333 said:

Okay, the trouble with posting when you're half-asleep is that your editing facilities are half-asleep as well.  For the record, that's a Sony VHS recorder and a Commodore 1084 monitor mentioned in the OP.  Thank you for ignoring my errors.

 

I found the MCM68766C35 is the wide-body version of the 2764 EEPROM; I have some on order.  Also on order are a couple of Hitachi 6309 CPUs which should be a drop-in replacement.  The cocovga adapter will have to wait until I get these other issues resolved.  I still want to see what I can do to upgrade the memory.  I believe this is a Revision E board.

 

Any suggestions?  Thanks,

-CH-

 

 

My tl866 eprom burner wont provide the higher voltage for those eproms.. i should fix that

 

[MrDave]

For your upgrade there is a schematic in a rainbow magazine..i believe your board has the 32k jumpers so if younput some 4164 rams in there you will be off to a good start

[clh333]

I can see three jumpers on the board near the memory.  All are set for 4/16k but have positions for 32k. Replace the 4116 with 4164 and set the jumpers to 32k?  Anything else to observe?

 

Thanks,

-CH-

 

 

[MrDave]

That should do it..  you will also need color vasic 1.2 not 1.0 gor 64k

[clh333]

Got a RS serial cable, 4-pin DIN, and used it to interface with an RS DMP105 which has both serial and parallel interfaces.  Found out that "LPRINT" is a syntax error as far as color BASIC is concerned but "LLIST" is legit.  Couldn't find a list of the device numbers but managed to get output to the printer with "PRINT #-2, "...  There has to be a better way.

 

-CH-

[MrDave]

From basic print #2   is the way to go.. or you can write your own ml routine.. or maybe better from 0s9 there are pokes to change the baud rate of the output..

Edited November 6, 2021 by MrDave

[MarkO]

On 11/5/2021 at 3:54 PM, MrDave said:

That should do it..  you will also need color vasic 1.2 not 1.0 gor 64k

I should "ship" you some of the MC65766's......

 

MarkO

[clh333]

5 hours ago, MarkO said:

I should "ship" you some of the MC65766's......

 

MarkO

The ones I ordered are somewhere east of here... a couple thousand miles.  It always seems a miracle to me when something arrives from China.  But they were going for $20 a pop from US sellers.

 

Ordered four; when I get them I will replace the Color BASIC 1.1 ROM as well as add the Extended Color BASIC ROM.

 

-CH-

[MarkO]

12 hours ago, clh333 said:

The ones I ordered are somewhere east of here... a couple thousand miles.  It always seems a miracle to me when something arrives from China.  But they were going for $20 a pop from US sellers.

 

Ordered four; when I get them I will replace the Color BASIC 1.1 ROM as well as add the Extended Color BASIC ROM.

 

-CH-

I ordered 20 or so a few years ago..  A few were not the MC68766, but I still have over 15 of them...   I updated the BASIC in my 26-3004....

 

MarkO

[jhd]

On 11/6/2021 at 6:39 PM, clh333 said:

Couldn't find a list of the device numbers but managed to get output to the printer with "PRINT #-2

 

On the Coco:

 

-2 is the printer (as you have discovered)

-1 is the cassette tape

0 in the screen 

1 is the first disk drive 

 

Under BASIC, the serial port is output only. There is a DLOAD command in Extended BASIC that is both undocumented and largely non-functional.  

 

(It has more than 30 years since I used a Coco, yet somehow I can still remember this stuff!)   

[clh333]

The Hitachi CPU and 4164 RAM have arrived, along with a 1372 I obtained in case of accidents screwing around with the video output, but the EEPROMs are still floating around in the mail system.  Rumor has it they're in this country.

 

jhd: Thanks for this info.  It's a different BASIC and I'm still learning.  I just acquired an RS232 cart as well, but none of the peripherals have yet been demonstrated to work with the CCI.

[MrDave]

Well you can start with 32k upgrade

[clh333]

The EEPROMS arrived in yesterday's mail.  From the Color Computer Archive I found the ROM files I want to use, but I have run into another problem:  Neither of my (USB) EPROM burners list a "device" such as the MCM68766C35.  There are no listings, among the devices, for Motorola at all, and I can't find a cross reference to something that IS listed.  

 

Does anyone know of a way around this?  Do I need a different programmer, or a custom programming service?

 

Thanks for your suggestions,

-CH-

[MrDave]

Yeah thats the problem with the obsolite eproms they need a 21 to 25 volt programming pulse..thats why i made those little converter boards.. Some folks have programmers that do those chips. I need to make an adapter for my tl866 to do them someday..  i have a few boards still in stock if you need..

[clh333]

 

3 hours ago, MrDave said:

Yeah thats the problem with the obsolite eproms they need a 21 to 25 volt programming pulse..thats why i made those little converter boards.. Some folks have programmers that do those chips. I need to make an adapter for my tl866 to do them someday..  i have a few boards still in stock if you need..

 

After further research I find that the 68766 requires higher voltage; the spec is 26 volts, and reportedly programming may fail at lower voltages.  One of my programmers* supposedly delivers 21V, although I have never required this voltage for previous uses.  It does, however, have an input for an external power supply; it may be that this would be required for 21V.

 

I also found some designs for DIY chip-specific programmers, implemented as Arduino "shields".  Is this the sort of converter board to which you refer?  Are its specs published anywhere?

-CH-

 

* GQ-4X; the other is TL866CS.

[MarkO]

12 hours ago, clh333 said:

 

After further research I find that the 68766 requires higher voltage; the spec is 26 volts, and reportedly programming may fail at lower voltages.  One of my programmers* supposedly delivers 21V, although I have never required this voltage for previous uses.  It does, however, have an input for an external power supply; it may be that this would be required for 21V.

 

I also found some designs for DIY chip-specific programmers, implemented as Arduino "shields".  Is this the sort of converter board to which you refer?  Are its specs published anywhere?

-CH-

 

* GQ-4X; the other is TL866CS.

 

I have a couple older Needham's EMP-20's that provide the Higher Voltage to program the MC68766's.   An Adapter that provides the Higher Programing Voltage sounds feasible...

 

MarkO

[clh333]

19 hours ago, clh333 said:

 

One of my programmers* supposedly delivers 21V, although I have never required this voltage for previous uses.  It does, however, have an input for an external power supply; it may be that this would be required for 21V.

 

I also found some designs for DIY chip-specific programmers, implemented as Arduino "shields".  Is this the sort of converter board to which you refer?  Are its specs published anywhere?

 

It turns out that the GQ's power input is only to supply 5VDC in the case of USB hubs that are unpowered.  No luck there. The MCM data sheet specifies 25VDC pulse voltage; MIN 24V, MAX 26V.

 

The converter board, which is an Arduino Mega "shield", is detailed here: 

http://www.mattmillman.com/projects/hveprom-project/an-easy-to-build-programmer-for-2704-2708-mcm68764-mcm68766-eproms/ 

 

I could only find bare project boards on eBay; the estimated cost of DIY is upwards of $60 and would take months to complete.  Some of the components are relatively hard to source.  So I am inquiring with custom programming services about the cost of having my ICs programmed.

 

-CH-