Help - trying to restore C1PMF

[drwass2]

Just got my C1P or superboard II running after 35 years in storage. It actually came up running ok but then died.
I am using an LCD monitor/TV using the video in (yellow, white, red RCA jacks). use the yellow only. Don't try it with component video using blue green etc RCA Jacks.

I found the best gadget for testing was a Radio Shack logic probe which indicates pulse. beside the standard hi, lo, open.
All the data and address lines should be pulsing. I had one locked HI (or Low). needed to replace the cpu chip.

Also had problem with the 74LS138 chip U23 which decodes the address for the video and keyboard access.
There was no pulsing at the pin 9 ouput which activate U20 which selects video or keyboard read and writes.
verified bad decoder chip by taking out the cpu and driving the address lines 15,14,13 directly to see if chip worked as it should.

Also had a BAD Ram chip 2114 which locked up the machine. i removed all the ram chips except the first two and saw if machine would power up with garbage on video screen (video runs independently of cpu). hitting the reset should
1)clear the screen 2) place D/ C/ W/ M/ on the screen and read keyboard. Mine wasn't clearing screen.

I removed all the BASIC ROM chips. just kept the monitor and one set of RAM. Got that to run,
then added RAM one set at a time till found bad chip that hung up system..

Good Luck. First thing is to get the random junk coming out of the video.

\I will publish my video mod later that you may want to implement.

GOOD LUCK

[dave]

It sure looks like 60 Hz. Where were you measuring this waveform?

Dave

[lowrybt1]

Dave,

That was from pin 8 U58 but I realized something after posting the image.... the on-board glass fuse blew some time earlier in the evening. So I have to get hold of another fuse. But wait, there's more.

I got hold of another 600 Board which lo-and-behold booted up, generated the garbage screen and then went to D\C\W\M. Keypress C gets me to BASIC. The board came with 8K which reported fully available. I hooked up my 610 Board which was fully populated with RAM and the system reports 30+K available. I probed pin 8 U58 and definitely saw the waveform I should see with a working oscillator.

As for the first board with no video, I am not giving up. I need to get the replacement fuse. Now that I am sure the signal coming off pin 8/U58 is bad is my next step to replace that IC or the crystal or both? Thoughts?

One other question -- this one about the new board. It has the RS-232 circuits populated and a RS-232 connector wired -- remarkably -- to the J3 using nails for pins. Here's my question\concern. There are only 2 wires that run to pins on the RS-232 connector. I've never seen a RS-232 hookup with just two lines running to the connector. Is there any chance this setup might work?

Thanks,

TOm

[dave]

There should be three pins, TX, RX, and GND. Perhaps only TX and GND are hooked up for a line printer?

[lowrybt1]

So, if I want to load programs through that port, I may be stuck. The other board I have has the same RS-232 components installed with a DB25 that has all the normal wiring -- but the wiring on board (and the trace cuts) for the cassette\serial port switch are very different than those on the working board.

I am tempted to take the fully-wired DB25 from the non-working board and plug it into the molex connecter on the working board. What are the chances it will work despite the different switch configuration and trace cuts? That's really a rhetorical question.

[dave]

If that section has been extensively rewired, then there's no telling what it's configured for. Look at the 600 board schematics on OSIweb.org to find the schematics for the serial section. One thing you could do is remove all the jumpers and restore all the cut traces, and then go forward from that point. Some things that could be modified:

The default configuration is 300 baud, since cassette use is expected. You may want to change this. For the 600, this is done by tuning an oscillator to 16x the desired baud rate. You may want to check if this was done (we'll get into details when you get there.)

Parts may be populated to work with RS232, although slightly nonstandard voltages. It is possible that this section was modified for 20 ma current loop, or RS 485, or something else. You probably want to restore the original wiring.

One alternative, if you just want to bypass the modified circuit for now, is to get a USB-to-TTL uart converter (These can be had for about $5. They are commonly used by hobbyists for arduino projects, etc.) And hook the Tx to the ACIA's RX line, and the Rx to the ACIA's TX line, and GND to the SBII Gnd. And you will have communication with your laptop, etc. You still will want to adjust the baud rate to somewhere around 9600.

Dave

[MK14HAK]

See MarkCsele's site for some god RS232 notes:

Connector J3 Wiring (for Cassette Tape operation):
•Jumper J3 Pin 5 to J3 Pin 6
Connector J3 Wiring (for RS-232 operation): •Jumper J3 Pin 4 to J3 Pin 6
•J3 Pin 2 (RS-232 Out) to DB-9 Pin 2 (Transmit to PC)
•J3 Pin 3 (RS-232 In) to DB-9 Pin 3 (Receive from PC)
•Board Ground to DB-9 Pin 5 (Ground)

J3 4 - 6 is the connection often missed

Mike

[lowrybt1]

Is there a POT on the 600 board that I can adjust to get better horizontal centering of video out?

I'm using an upconverter to connect the composite out to the HDMI port of a LTD TV. Looks greater but the first character on the left side of the screen is truncated. So characters 2 through 24 display cleanly left to right. My TV does not have an adjustment option to recenter or adjust vertical/horizontal.

Thoughts?

[dave]

Hi Tom,

There's not much you can do, since the HSYNC is derived from the timing chain. Assuming the HSYNC is not already at the lower margin, you could try shortening it to give a longer back porch, which can move the video to the right. But you can only shorten so much before losing the sync. You could try replacing R34 (10k resistor) with a 4.7k resistor and a 10k pot, and see what happens.

Have you considered picking up an old monitor on Ebay? Something like this:

http://www.ebay.com/itm/Ikegami-PM-909- ... 5b0f022aa9

Might be perfect.

Best regards,

Dave

[dave]

One thing to note: If you do this, you'll still want to increase the baud rate from 300, to make transfers bearable. The 6502 at 1MHz can support in excess of 9600 baud. For the 600 board, the clock is derived from the master timing chain. The 3.932160 MHz clock is divided down to provide timing for the video circuitry as well as the ACIA. U57 and U63 form a divide-by-24 counter to provide the 16x serial clock. The input to this 24-pin divider is pin 2 of U57, which is normally connected to pin 14 of U59, the div32 tap, which yields a baud rate of 300 bps. To get 9600 bps, you will want to drive pin 2 of U57 directly from the master clock signal, pin 3 of U58. This involves cutting the tract between U57 pin 2 and U59 pin 14, and jumpering U57-pin2 to U58-pin3 with a short length of wire.

Dave