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Author Topic: C7420 documentation  (Read 7526 times)
manopac
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« Reply #15 on: May 06, 2009, 11:52:25 PM »

Sounds very familiar...  Sad

fixable ? what is it ? (it looks like the code of the cart is run but not the one on the z80 or the communication between them ...)

And your PC was not connected to ground?

it was my notebook and I didn't do anything ... how can I avoid it happening again ?
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Rene_G7400
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« Reply #16 on: May 07, 2009, 12:50:47 AM »

fixable ? what is it ? (it looks like the code of the cart is run but not the one on the z80 or the communication between them ...)

Yes, that's exactly what's (not) happening, the 8048 doesn't get the proper response from the Z80, so that can have many causes. Probably fixable, but the problem might be difficult to find.

And your PC was not connected to ground?

it was my notebook and I didn't do anything ... how can I avoid it happening again ?

Was the power supply of your notebook plugged in? If it was, have you used a grounded power outlet? (You should.) You can avoid it by disconnecting the power supply of your notebook (using the battery only), or by following this order of connecting things:

- C7420 cartridge in G7400
- audio plugs of C7420 to notebook
- video or RF cable of G7400 to TV
- power cable of G7400 to power outlet
- power supply of notebook to power outlet

Disconnecting should be done in the reverse order.
It would be best to connect both audio plugs of the C7420 to your notebook. It would be even better if you are sure that both your notebook and your TV are connected to ground somehow.
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manopac
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« Reply #17 on: May 07, 2009, 08:01:38 PM »

Yes, that's exactly what's (not) happening, the 8048 doesn't get the proper response from the Z80, so that can have many causes. Probably fixable, but the problem might be difficult to find.

Sad

Was the power supply of your notebook plugged in? If it was, have you used a grounded power outlet? (You should.) You can avoid it by disconnecting the power supply of your notebook (using the battery only), or by following this order of connecting things:

- C7420 cartridge in G7400
- audio plugs of C7420 to notebook
- video or RF cable of G7400 to TV
- power cable of G7400 to power outlet
- power supply of notebook to power outlet

Disconnecting should be done in the reverse order.
It would be best to connect both audio plugs of the C7420 to your notebook. It would be even better if you are sure that both your notebook and your TV are connected to ground somehow.


power supply was plugged in - I suppose by "grounded outlet" you mean one of those "fat" plugs (not the 2 stick small ones)

so its best to use only battery powered notebook ? and switch on the G7400 first ? I always thought its better to have the notebook running first to avoid some high peak when turning it on ...
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Rene_G7400
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« Reply #18 on: May 07, 2009, 10:49:59 PM »

power supply was plugged in - I suppose by "grounded outlet" you mean one of those "fat" plugs (not the 2 stick small ones)

Something like this:


so its best to use only battery powered notebook ? and switch on the G7400 first ? I always thought its better to have the notebook running first to avoid some high peak when turning it on ...

If you use only battery powered notebook, you can turn it on first.

The problem with most power supplies (switching types, as found in computers, TV's and in the G7400) is that some current leaks from the primary side to the secondary side, which can cause a pretty high voltage on the connectors of the device. Since the current is low, this is harmless for humans, but it can destroy sensitive equipment. That's why devices with that kind of power supply should always be connected to ground.

Have you taken the coupling cartridge of the C7420 out of the G7400 when the audio cables of the C7420 were still connected to the (powered) notebook?
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manopac
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« Reply #19 on: May 07, 2009, 11:34:40 PM »

Something like this:

thats the one I was talking about :-) my notebooks powersupply has one of those

If you use only battery powered notebook, you can turn it on first.

The problem with most power supplies (switching types, as found in computers, TV's and in the G7400) is that some current leaks from the primary side to the secondary side, which can cause a pretty high voltage on the connectors of the device. Since the current is low, this is harmless for humans, but it can destroy sensitive equipment. That's why devices with that kind of power supply should always be connected to ground.

Have you taken the coupling cartridge of the C7420 out of the G7400 when the audio cables of the C7420 were still connected to the (powered) notebook?


ok ... got that ...

I thought the cart went once I plugged the audio cables into the (running) notebook (from the running G7400) ...

wann hear something funny ? I just took the cart apart ... unplugged and replugged all the connectors on the cartridge and on the Basic-Part side and plugged it in without casing .... and it worked ... so I put all the casing back on ... and it still works :-)

current count: 3 C7420 working - 0 broken :-)

lets see how this changes over the next few weeks ...


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Rene_G7400
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« Reply #20 on: May 08, 2009, 12:43:35 AM »

wann hear something funny ? I just took the cart apart ... unplugged and replugged all the connectors on the cartridge and on the Basic-Part side and plugged it in without casing .... and it worked ... so I put all the casing back on ... and it still works :-)

current count: 3 C7420 working - 0 broken :-)

That's good news!

Yes, the connectors of the cable which connects the cartridge to the module can cause problems too. I forgot about it, but I've had that problem too once. It never came back after unplugging and replugging the connectors once.

The problem I've had with the C7420 after I had made a mistake with the order of connecting it was easy to fix, only the input amplifier (LM339) needed to be replaced. So the module was still working, but you couldn't load a program from tape anymore. After the repair I've added two diodes to the input to prevent overload.
The cause of the problem with the other module was a lot harder to find.
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Rene_G7400
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« Reply #21 on: May 15, 2009, 04:01:02 PM »

I've studied the disassembly of the 8048 ROM of the Basic module, and I've found some really interesting things. For example, there are two routines to receive data from the Z80 module and send them to the VDC, so I suppose if you write a Z80 assembler program and load it into the module through Basic, it should be possible to write a game which uses the VDC.
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Rene_G7400
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« Reply #22 on: May 23, 2009, 08:57:19 PM »

A few results from some C7420 experiments this weekend:
- thanks to the BASIC command: CLEAR 50,-2 , I'm now able to use the complete 32k RAM of my modified BASIC module
- I don't need to open a C7420 anymore to make a dump of the Z80 ROM's, it can be done with the BASIC command: CSAVEM "romdmp",0,16384 . I record the audio signal of the tape output with my computer, and convert the sound file with my tools to a .bin file.
The contents of the RAM can be dumped the same way for experiments.
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Rene_G7400
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« Reply #23 on: June 06, 2009, 03:47:39 PM »

With a Z80 assembler program I now can send data from the C7420 module to the VDC, so a game written for the C7420 in Z80 assembly can control both video chips of the G7400. Since the sound is generated by the VDC too, it is also possible to create different sounds with the C7420 besides the 8 default sounds.
No hardware modifications were required to make this work, so programs like this can run on any C7420.
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manopac
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« Reply #24 on: June 09, 2009, 03:25:42 PM »

- thanks to the BASIC command: CLEAR 50,-2 , I'm now able to use the complete 32k RAM of my modified BASIC module

what modification did you do ?
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Rene_G7400
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« Reply #25 on: June 09, 2009, 05:52:23 PM »

- thanks to the BASIC command: CLEAR 50,-2 , I'm now able to use the complete 32k RAM of my modified BASIC module
what modification did you do ?

Just added two TMS4416 chips (as mentioned in the service manual), and a few minor improvements, like a power indicator LED, a tape input LED, over-voltage protection on the tape input and lower impedance of the tape output.

One other C7420 module has a modified 8048 ROM to work on the Odyssey3.
« Last Edit: June 09, 2009, 05:54:26 PM by Rene_G7400 » Logged
Dr.Wily
Trying to get the cartridge in...
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« Reply #26 on: May 14, 2018, 02:39:34 AM »

Hello,

What are you using to plug input audio (white connector) of the C7420 ? The jack male connector does not fit into female connector.
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partyicebear
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Retro time


« Reply #27 on: May 14, 2018, 10:34:55 PM »

Hello,

What are you using to plug input audio (white connector) of the C7420 ? The jack male connector does not fit into female connector.

Its a usual 2.5mm headphone plug. So you can plug it into a computer ear or amplifier phone jack.
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Dr.Wily
Trying to get the cartridge in...
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« Reply #28 on: May 15, 2018, 01:20:33 AM »

The connector don't fit into my MP3 player plug, nor in a 3,5mm to 6,5mm jack adaptor. It don't fit in my laptop too.
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partyicebear
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Retro time


« Reply #29 on: May 18, 2018, 01:14:39 AM »

Strange...other sources tell about or show the usage of the 3.5mm jack
Description: http://www.cyberroach.com/vidpac/vidhard/new_vid_c7420.htm
Picture: https://goo.gl/images/ns2b6H
Video https://youtu.be/bmwI0AMnkCw

Does your white connector look different?
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