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I was making backups of old turbo-tapes to disk and noticed that the quality was very poor on some tapes. I have a LOAD-IT datasette with a signal meter. Problem with it was, that I could turn the knob (head alignment) 45 degrees and still have same two(lousy) bars on the meter. There was a need for something more accurate when adjusting the alignment to get the best signal while reading the tapes.

 

My solution was to implement an analogue VU-Meter to show the signal strength and a possibility to listen in on the signal to determine if its data or other information(music).
 
Update 2015-04
Information on how to build a VU-Sette : http://blog.worldofjani.com/?p=1477
 

 

vu-sette1
Down right, a 22 mm hole is drilled for the (obvious) VU-Meter.

 

vu-sette2
The VU-meter itself is from a batterytester, hence the text 🙂

 


In action

 

FinalTAP Result
A quick comparison with FinalTAP on two .tap images. Left tape has been read with “VU-Sette” and right tape with LOAD-IT. I tried several reads with LOAD-IT but the result was pretty much the same. There is nothing wrong with LOAD-IT, as long as you got a good signal on the recorded media.

In my case, “VU-Sette” allowed me to adjust the head more precisely and get out a (much)better read of the tape. For you who are not familiar with FinalTAP, its a tool for examining, cleaning and restoring digitized data cassette tapes (TAP files) for the Commodore 64 computer.

 

 

 


The first version of c128d had the same motherboard as the c128. The later c128dcr (cost reduced) had a different motherboard.

Pictures of c128 and c128d (not dcr) for comparsion.

c128mobo

c128dmobo

 

 

 

To create a cartridge for your C64 in the simplest form, is wiring a 8K ROM to the expansion port.

The CPU can only see a maximum of 65536 bytes. Adding a cartridge will not give you additional memory, instead it will replace memory at $8000, $A000 or $E000 depending on how ROML, ROMH, EXROM and GAME lines are being handled in the expansion port.

It is possible to bank in and out ROML/ROMH areas to gain access to different banks or RAM. This is how EasyFlash cartriges provide 1MB to the C64, it however only sees 16K of the 1MB at a time.

 

 

There are basically three types of cartridges for the C64:

8K Cartridge, $8000-$9FFF (ROML).
GAME = 1, EXROM = 0
ROML is read only. Basic ROM and Kernal ROM are available.


16K Cartridge, $8000-$9FFF / $A000-$BFFF (ROML / ROMH).
GAME = 0, EXROM = 0
ROML/ROMH are read only, Basic ROM is overwritten by ROMH.


16K Cartridge, $8000-$9FFF / $E000-$FFFF (ROML / ROMH). Ultimax mode.
GAME = 0, EXROM = 1
Ultimax mode is an emulation of the Japanese CBM machine called “MAX”. It is a predecessor of the C64 with less RAM. In Ultimax mode ROMH replaces the kernal at $E000. You do not need ROML for a cartridge to function and can be left out.

 

 

Cartridge autostart
When starting up, the CPU will load the reset vector from $FFFC/$FFFD into the program counter and continue from there. If a normal cartridge is present, it executes the kernal and checks for a cartridge identifier string.

cbm80
Kernal will look for the string “CBM80” at $8004- and will do a “JMP($8000)” if found.

If an Ultimax cartridge is inserted, the kernel is overwritten by ROMH and therefor $FFFC/$FFFD must point to your code.


8/16K Cartridge code example

 

 

Test the code above with WinVICE:

 

 

Commodore 64 Expansion port pinout:

Expansion Port

 


 

8K Cartridge $8000-$9FFF

8Kcart_8000


16K Cartridge $8000-$BFFF


16K Cartridge $8000-$BFFF (Single chip version)

16K cartrige at $8000-$bfff

A 27128 chip and a two input AND gate consisting of two diodes and a resistor. You can also use a 74LS08.


 

8K Cartridge $e000-$FFFF (Ultimax, no ROML at $8000)
You can create a 16K Ultimax cartridge by adding a 8K EPROM and connect it to ROML($8000-$9FFF).

8K cartrige at $e000 (ultimax)


 

Link(s):
Check out SukkoPera’s Open Hardware 8Kb Cartridge at: https://github.com/SukkoPera/OpenC64Cart
 


 

Update 2015.12: Corrected an error in the 16K cart schematic. EXROM/GAME should be connected and not IO2/EXROM. Text was correct but QC slipped on the drawing. Thanks to mATE for notifying me about it.
 
Update 2016.01: Updated Ultimax cart schematic with $e000-$ffff. Text was correct but again QC has slipped on the drawing. Thanks to Bart for the heads up.
 
Update 2017.12: Added single chip 16K schematic.
 


RapiDOS professional is a floppy speeder based on the Professional DOS by Klaus Roreger. More information on Professional DOS can be found at : http://www.d81.de/ProfessionalDOS/ and http://ar.c64.org/wiki/Category:Professional_DOS

RapiDOS was sold in the US by Chip Level Designs with kernel code written by Lawrence Hiller (aka Mr.Nike). Mitch/ESI gave ideas and feedback to the code resulting in RapiDOS having lots of “hacker enhancements” over Professional DOS, for example the built in monitor. It also functions on PAL (50Hz) Machines.

On this page you will find pictures of the RapiDOS hardware. The ROMs are also available for download.

Thanks to Mitch / ESI for information and for the hardware/ROMs !

 
Update: Added a .pdf with all reviews and advertisements regarding RapiDOS from Ahoy/Info/Gazette Magazines. Thanks to Stone Oakvalley for the information 🙂

Interesting to note is that Compute Gazette Issue 51 (1987-09) has an advertisement saying RapiDOS is “soon coming” and in Issue 54(1987-12) it is available. Later on C128 and CP/M is mentioned to be supported.

 


 

1541 with RapiDOS professional
Drive controller board and the CIA board installed. The wire lead is used for switching the RapiDOS on and off through the User-port board.

 


RapiDOS Professional User-port Board.
Switch to the left turns on/off the RapiDOS in both the C64 and the 1541.


C64 ROM Adaptor board

[No picture available]
The C64 ROM Adaptor board has a wire lead connected to the User-port board.

 


More pictures of RapiDOS Professional.

 

 

 

Replacing a 2364 ROM with a 2764 EPROM requires an adapter. You can use a 2364 to 27128 adapter to be able to switch between two different ROMs (ex: cbm original and a floppy speeder kernal).

 

2364 to 2764 adapter

2364to2764

 

2364 to 27128 adapter

2364 to 27128

R1 = 4.7k ohm
J1 = Switch

 

While making backups of some disks(Commodore 5,25 disks with a Zoomfloppy) I noticed that the reading error-rate was very high. The disks are from the mid 80;s but they can survive depending on how they have been stored and what not.

I could get a big variety of errors on totally different sectors while (re-)reading a disk. I cleaned the R/W head, disks, used different transfer-programs, speeds, copied disks to another media on the native system etc. (even had some ridiculous amounts of read retries) and yet nothing helped.

Another thing that was a bit concerning was the mylar coating (recording media) took some serious beating for every read. I could see on the surface where the R/W head had passed. Some disks even lost the coating, leaving a transparent plastic behind.

 


…condition after a couple of reads, Track 18 “visible” in the middle.

 

It was obvious that these disks didn’t have unlimited reads and with the varying read results I decided to gather some data.

To make a long story short… the disks are stored as image-files ( .d64) and include a separate block for the error-information. This is where I started looking.

First I made a tool to visualize the data and then I extended it to gather sectors from different disk images(same content) and combine them to as close to a whole image as possible.
d64eic1
Read # 1. Errors: 26

 

d64eic2
Read # 2. Errors: 10

 

d64eic3
Read #3. Errors: 10

 

d64eic4
Images 1 and 3 combined. Errors: 7

 

d64eic5
Images 1, 2 and 3 combined. Errors: 1

 

Combining the data from the three images resulted in an image with (just)one bad block.

 

 


 

Download:

Limitations:
* Version v1.0 does not support 40 track disks.

 

 

Diagnostic cartridges for the Commodore 64 / 128.

A bunch of diagnostic carts. Some of the material below is from the web and some of them are from my own collection.

C64
You will probably be fine with the C64 Dead Test (Rev 781220) and C64 Diagnostic Kit 326070-1 (Rev 586220/588220) for the C64. Use the C64 Dead Test if you got a blank(black) screen, it will flash the border according to which RAM circuit is broken.

C128
If you got a C128 with a blank(blank) screen you can use the C64 Dead Test to find faulty (low) memory. When the C64 side is working, use the C128 Diagnostics to verify the upper memory. It is also possible to rewire the high and low memory and then give the C64 Dead Test a second run. C128 Diagnostic Carts use the same harness as the C64 Rev.586220 (326070-01) but with a different keyboard adapter.

Testing in VICE
You can test the carts in vice:
C64: x64.exe -cartcrt [cartname].crt
C128: x128.exe -extfunc -extfrom [romname].bin

Additional credits:
Peter Schepers, Nicolas Welte, DLH’s Commodore Archive, SLC, Zoran, Doc64, Sierohpätsch, Jeroen Vlasveld (http://myoldcomputer.nl), Dutch Commodore Club.

Updates:
2014-11: I have now included both C128 and C128D keyboard connector schematics for Rev.785260 to avoid misunderstandings. There are also some notes about the connector at position 1.4.8 in the manual.
2015-01: Added disassembly of the C-64 Diagnostic Rev 4.1.0. This was a bit tricky to disassemble(reassemble) as it crossreferences code between $8000/$1000.
2015-01: Added C-64 Diagnostic (Box) (324528-02). Thanks to SLC and Zoran.
2015-01: Added C-128 DCR Integral Diag 1.0 and C-128 Diag Rev.588121. Thanks to Zoran.
2015-01: Thanks to Boulderdash for the info about the C128 Serial Adapter.
2015-10: On request, I made a disassembly of the C64 Diag 781220 deadtest.
2016-11: Added Rossmöller / Roßmöller Doctor64 diagnostic. Thanks to DOC64 and Sierohpätsch.
2018-12: Added C-64 Diagnostic Rev 4.1.1 and Import Test Diag.
2018-12: Added C-64 Diagnostic Rev 3.7.3. At a meeting held by the Dutch Commodore Club, Jeroen Vlasveld noticed a diagnostic harness not present on this page. He sent over the diagnostic Rev 3.7.3 ROM, a picture and a schematic of the harness. Thanks!

 

Don’t miss the updated Diagnostic 586220+ with kernel detection and other fixes.

 


 

C-64 Dead Test Kit (CBM 314139-03)

dead test
Rev. 781220. Located at $E000 in memory(ultimax) and boots before kernal ROM.

Cartridge ROM: C64 Dead Test Rev 781220 Diagnostic Cartridge (314139-01)
Manual: C64 Dead Test Diagnostic Manual (314139-02)

 


 

C-64 Diagnostic Assembly Kit (CBM 326070-01)

diag-c64_586220

Rev. 586220 (c64)  and 588220 (sx64)

Located at $8000 in memory and requires a harness (some tests work without the harness).
Note: There are atleast 3 variations of the schematic on the net, two of them are missing an interconnected wire in the casetteport.

Cartridge ROM: C64 Diagnostic Rev 586220/588220 Cartridge (314061-01)
Manual: C64 Diagnostic Instruction and Troubleshooting Manual (314061-05)
Harness Schematic: C64 Diagnostic Harness Schematic (314061-02/03/04)

I disassembled the cartridge for studying purposes. It can be compiled(assembled) with 64tass.

 


 

C-64 Diagnostic Rev 3.7.3, Rev 4.1.0, Rev 4.1.1 and Import Test Diag



Located at $8000- in memory and use harness 251169-02.

C-64 Diagnostic Rev x ROMs. I dug out all diagnostics visually alike and disassembled them, after aligning code and comparing routines it became obvious these four were from the same codebase. Some testroutines are identical with the 586220 allowing it to pass, but the correct harness is 251169-02. Import Test Diag is modified to work without a harness.

 


 

C-64 Diagnostic (Box) (CBM 324517-02)

Located at $8000- in memory and uses its own harness. See also Roßmöller Doctor64 below.
Cartridge ROM: Prog. for Diagnostic Box (324528-02)

Roßmöller Doctor64

Located at $8000- in memory and uses same harness as Diagnostic Box (324528-02).
The Roßmöller will give a false “Interrupt BAD” on C64C models. Interesting is that the Diagnostic Box (324528-02), which can be found on a Commodore spare parts list, has identical check routines as Doctor64 except for the Interrupt part.

 


 

C-128 Diagnostic Rev. 588121

Rev. 588121
Uses the same harness as the C64 Rev.586220 (326070-01).

 


 

C-128 Diagnostic Assembly Kit (314060-01)

785260_ok

Rev. 785260
Uses the same harness as the C64 Rev.586220 (326070-01).

Cartridge ROM: C128/128D Diagnostic Rev 785260 Cartridge (314061-06)
Manual: C128 Diagnostic Instruction and Troubleshooting Manual (314061-09)
C128 Diagnostic Keyboard Adapter (314061-07).
C128D Diagnostic Keyboard Adapter (314987-01).
Note: C128 Serial Port Connector has Pins 1 and 5 connected.

 


 

C-128 Diagnostic Rev. 789010

789010_ok

Rev. 789010
Uses the same harness as the C64 Rev.586220 (326070-01).

 


 

C-128 Diagnostic Rev 1.1 and 1.4 (325099-01)

C-128 Diagnostic Rev 1.x Uses its own Cart and harness.

 


 

C-128 DCR Integral Diag 1.0 (325109-01)

Cartridge ROM: C-128 DCR Integral Diag 1.0 ROM (325109-10)


 


 

A machine displaying less than 38911 free bytes or “?Out of memory error in 0” is often an indication of malfunctioning RAM. If several RAM-chips are broken, or shorted, you will be greeted with a blank(black) screen.

Free basic memory is verified when the computer boots up. It starts checking the memory from location 2049($0801) and goes upwards. If you get “3 bytes free”, it indicates a problem at address position 2049+3=2052($0804).

Even if RAM-chips are failing, it does not mean that every byte has a failing bit, this is why you need to test a larger area of memory. In the example above, 3 bytes passed the test.

Many fastload cartridges(The Final Cartridge or Action Replay etc.) skip the RAM-test to speed up the boot sequence. These will always display “38911 Basic Bytes free” regardless of RAM status.

Broken RAM is usually a sign of a bad powersupply. The components inside the PSU deteriorates and therefor delivers higher voltage than it should. RAM circuits are sensitive to overvoltage and are often the first to go.

Failed RAM can get very hot(burn-your-fingers-hot) and is easy to find, but that is not always the case. Some machines can even have broken memory that are a mix of “hot and cold” chips.

Depending on the C64 motherboard revision, you either have 2 or 8 RAM-chips. For the C128 it is 4 or  16 chips.
C64: 2 x 41464 (64kbit x 4) / 8 x 4164 (64kbit x 1)
C128: 4  x 41464 (64kbit x 4) / 16 x 4164 (64kbit x 1)

Replacing two chips is not that much of a work, but with 8 or 16 chips you want to know which one(s) are broken.

C64s with 8 memory chips also have two multiplexers; MOS7708(identical to 74257) located at U13 and U25. It is more seldom these fail but they should not be neglected.

 

There are a couple of ways finding failing RAM:


 

1. Piggybacking.
You insert a known working chip on top of a chip on the PCB. All legs must have good contact, bend the legs slightly inwards on the piggyback chip and work your way through all RAM. You can piggyback several IC;s, just make sure your equipment is powered off and that your PSU is working properly(so it won’t burn even more RAM). If the amount of free RAM changes when turning on the computer, replace that RAM-chip.

 


 

2. Calculating BITS

Each BIT on every BYTE is handled by a RAM-chip. Depending on which BIT is malfunctioning, you can determine which RAM-chip is broken.

Test every memoryposition with the byte combinations in TABLE 1. After that use TABLE 2 to determine which chip has failed. Remember that bit 0 is the rightmost and bit 7 is the leftmost bit.

The behavior of the “wrong bits” are because the broken RAM-chip either keep a data line high or low when it shouldn’t.

A couple of ways to figure out which bit is failing:

Visually check bytes on the screen
Inspect the start-up screen(or whats left of it). It is normally mostly filled with “space”-character (hex 0x20). If there are other chars than space, for example “!”-character (hex 0x21) you can determine that there is a failing RAM that handles bit 0, another example is a “%”-character (hex 0x25) indicating that bits 0 and 2 are failing in that specific memory location.

Action Replay monitor (or any other cart)
Use a machine code monitor to fill the memory and find the differing bytes.

Use basic routines POKE and PEEK
In the first example, with problems at address 2052($0804), use the following command: “POKE 2052,x : PRINT PEEK (2052)” where x is from TABLE 1. The result in and out should be the same, if not, take the differing bits and check with TABLE 2.

TABLE 1 – test bytes

binary hex dec binary hex dec
00000000 $00 000 11111111 $FF 255
00000001 $01 001 11111110 $FE 254
00000010 $02 002 11111101 $FD 253
00000100 $04 004 11111011 $FB 251
00001000 $08 008 11110111 $F7 247
00010000 $10 016 11101111 $EF 239
00100000 $20 032 11011111 $DF 223
01000000 $40 064 10111111 $BF 191
10000000 $80 128 01111111 $7F 127
10101010 $AA 170 01010101 $55 085

TABLE 2 – bits vs chips

BIT C64A,B C64B3 C64E C128,C128D C128DCR
0 U21 U10 U10 U38/U46 U38/U40
1 U9 U10 U10 U39/U47 U38/U40
2 U22 U10 U10 U40/U48 U38/U40
3 U10 U10 U10 U41/D49 U38/U40
4 U23 U9 U11 U42/U50 U39/U41
5 U11 U9 U11 U43/U51 U39/U41
6 U24 U9 U11 U44/U52 U39/U41
7 U12 U9 U11 U45/U53 U39/U41

 


 

3. Use a diagnostic program or cart
There are several diagnostic programs that test the memory for you. The Commodore diagnostic cartridges “C64 Dead Test Rev.781220” and “Diagnostic Rev.586220” are both good for this.

The “C64 Dead Test Rev.781220” cartridge is able to find broken RAM even with a blank(black) screen. It flashes the screen according to which bit fails. This one will save you a lot of time and work 🙂

Both cartridges are available at the Diagnostic Carts and Manuals page.
If you are interested to see how the memory is verified, there is also a disassembly of the Diagnostic Rev.586220 cartridge.

 


 

Parallell cable for Oceanic (OC-118) / Excelerator Plus drive.

You need to connect the following pins (identical to 1541). This drive works with Zoomfloppy.

 

There are four screws that hold the bottom plate, turn the drive upside down and remove the screws. Now you have access to the PCB.

 

Locate the correct chip by the pictures below (i soldered the wires directly to the legs).

Parallell cable for Oceanic (OC-118) / Excelerator Plus

 

Parallell cable for Oceanic (OC-118) / Excelerator Plus closeup