C128DCR C128 section only 12 V usage, without 12 V= problems

c128dcr
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Posts: 11

C128DCR C128 section only 12 V usage, without 12 V= problems Jan 2, 2015 14:14:03 GMT

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Post by c128dcr on Jan 2, 2015 14:14:03 GMT

Hello.
I bought a C128DCR machine. The PSU faultless, the machine works.
I wanted to recognise the function of the machine, I looked at this:
www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/index.html
I disconnected the +12 V= and 11 V~ voltages.
Why does not start the machine only with +5 V= voltage? Empty black screen.
On the schematics only to the 1571CR and the 8580 SID necessary +12 V= voltage.
SID CR17: www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/c128dcr-2-left.gif
U109 1571CR: www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/c128dcr-5-right.gif
I do not see more place where the machine uses +12 V=.
I connected the +12 V=, the machine works.
The 11 V~ uses the datassette port only, from 11 V~ to 9 V= to cassette motor 6 V=, and user port 10-11 pins.
www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/c128dcr-1-left.gif
Ideas?

Last Edit: Jan 2, 2015 14:24:03 GMT by c128dcr

hydrophilic
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Posts: 794

C128DCR C128 section only 12 V usage, without 12 V= problems Jan 4, 2015 9:39:15 GMT

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Post by hydrophilic on Jan 4, 2015 9:39:15 GMT

I investigated the datasette port... it seems to only drive less than 9V DC... I *really* wanted to use it for S-VIDEO power, but 6V DC (?) is not enough!

Err, sorry, I don't understand what is your question... ideas? Well, I used 9V AC from UserPort to create 12V DC for my S-VIDEO adapter... it works for me but (maybe) because it draws very little power (about 64 mA). In other words I get 12V DC with a simple circuit from the 9V-AC of the user port to make video work... I never got S-Video to work from the Cassette-Port (voltage too low... 6V DC?)

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c128dcr
Windows User

Posts: 11

C128DCR C128 section only 12 V usage, without 12 V= problems Jan 4, 2015 11:25:09 GMT

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Post by c128dcr on Jan 4, 2015 11:25:09 GMT

11 V~ to +9 V= unreg conversion, than +9 V= unreg to 6 V= conversion to cassette motor. CR 301 zener diode. Look:
www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/manual/82.gif
The question:
Why does not start the C128DCR with +5 V= voltage only? No 12 V=, no 11 V~. 5 V= only = empty black screen. Why?
All chips (minus U109 chip) use 5 V=.
There is not explanation on the schematics onto the black empty screen. 82-86.gif:
www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/manual/index.html

Last Edit: Jan 4, 2015 11:26:21 GMT by c128dcr

hydrophilic
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Posts: 794

C128DCR C128 section only 12 V usage, without 12 V= problems Jan 6, 2015 6:54:23 GMT

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Post by hydrophilic on Jan 6, 2015 6:54:23 GMT

Ah I totally missed the zener diode CR 301. Well that explains my problem with cassette/s-video, so thank you!!

Looking at schematic from Zimmer's, there I don't see a reason it should fail with only +5V.

But from the original C128 schematics (I tried to capture image, but Windows 8 sucks), the Z80 clock line is driven by +12V line. I don't own DCR so I can't say for sure which schematic is accurate... BUT if your DCR does use +12V like my flat C128 then that would explain the problem. (Remember the Z80 starts the computer, no matter what mode you select... no Z80 = black screen)

Edit

Captured schematic from C128 PRG and highlighted +12V line to Z80

/Edit

Last Edit: Jan 6, 2015 7:13:48 GMT by hydrophilic: Added schematic

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c128dcr
Windows User

Posts: 11

C128DCR C128 section only 12 V usage, without 12 V= problems Jan 6, 2015 10:43:34 GMT

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Post by c128dcr on Jan 6, 2015 10:43:34 GMT

No C128(D), C128DCR! This schematics = C128(D)! C128DCR no 12 V Z80, 5 V only.
C128DCR schematics 82-86.gif: www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/manual/index.html
I looked at the my C128DCR motherboard. The 12 V= connect onto places which can be seen on the schematics only.
Why does not start the C128DCR with +5 V= voltage only?

Last Edit: Jan 6, 2015 10:47:16 GMT by c128dcr

hydrophilic Global Moderator Posts: 794	C128DCR C128 section only 12 V usage, without 12 V= problems Jan 14, 2015 6:05:56 GMT Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by hydrophilic on Jan 14, 2015 6:05:56 GMT Well, if you physically verified the D(CR) schematics are accurate (I can not) then this is a great mystery! I hope somebody will post the answer because now I am very curious!!
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c128dcr
Windows User

Posts: 11

C128DCR C128 section only 12 V usage, without 12 V= problems Jan 14, 2015 10:46:19 GMT

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Post by c128dcr on Jan 14, 2015 10:46:19 GMT

I was hoping, I find here min. 1 man who knows the function of the C128DCR.
With +12V, but without U109 = machine start OK.
With +12V, but without U112 = machine start OK.
With +12V, but without U60 = machine start OK.
With +12V, but without U57 = machine start not OK. This normal.
www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/manual/83.gif
I will find the reason.

Commodore 128

C128DCR C128 section only 12 V usage, without 12 V= problems

Post by c128dcr on Jan 2, 2015 14:14:03 GMT

Post by hydrophilic on Jan 4, 2015 9:39:15 GMT

Post by c128dcr on Jan 4, 2015 11:25:09 GMT

Post by hydrophilic on Jan 6, 2015 6:54:23 GMT

Post by c128dcr on Jan 6, 2015 10:43:34 GMT

Post by hydrophilic on Jan 14, 2015 6:05:56 GMT

Post by c128dcr on Jan 14, 2015 10:46:19 GMT

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