Help - trying to restore C1PMF

[lowrybt1]

Thanks Dave.

The C1P I'm working with had what I think was a fairly standard factory installed PSU -- an arrangement I simply do not like. The transformer steps down the 120VAC to 15VAC which is delivered to a series of components on and off of the system board to drop and convert the voltage to 5VDC. There was a square bridge rectifier soldered to the bottom of the board, a large electrolytic capacitor soldered on top of the board and an op-amp attached to the C1P case. The op amp was the last component in the series. The multimeter indicated 7.7V DC coming off the op-amp and headed to the system board power rail. That's worrisome.

So, before scanning other components, I have eliminated the voltage and cycle conversion components -- basically taking the system board back to a near-pristine state equivalent to the OSI and SAMS schematics and images. Gone is the AC step-down transformer. In its place I'm installing a new, enclosed 5V 3A PSU from Jameco to directly feed the system board. Doing that tonight.

While waiting for the transformer to arrive, I have pulled and reseated all of the socketed chips. Some -- especially the 6502 -- had a lot of black residue on the pins which I removed carefully with a rubber eraser.

Let's see what happens tonight when a clean PSU is hooked up to the board.

[Klyball]

Hi Tom

3A is not enough to power both boards with full memory , don't connect the 610

Grant

[lowrybt1]

Understood. I took your good advice and set aside the 610 at the very start of the process. I do have a 5V 10A PSU to power both if\when that time comes. Thanks, Tom

[drwass2]

first of all I would totally disconnect the additional board with the drives and its memory and just get the basic single board C1P up and running first.
I just pulled mine out of the box after about 30 years and it came up running. I was amazed.. Stickky keyboard problems, but just banging keys a whole bunch of times starts to fix that somewhat.

I also did not have my old monochrome monitor and wasn't sure what I would do, but I plugged the video out directing into the yellow video input jack of a modern flat panel LCD monitor and it worked. Make sure your not using the composite video with green blue etc.
You want the old analog video input with just a yellow (video) and red and white (audio) RCA jacks. Plug the video into the yellow and it should work.
Actually the input is so sharp it looks weird because the dots are actually small squares.

I'm working on documenting my 64 character mod which you may eventually want to implement. Its the easiest there is.
Good luck and keep posting.

1) check voltage for 5 V.....may want to put in the LED on the board if it doesn't have one.
2) check for clock signals coming from the crystal and eventually going to the video scanning chips. I will post later where to look for this.
3) on power up, you should get a screen of garbage, because the video ram chips have not been fill up yet. Hitting the break key will
clear the video and come up with the M D W C or whatever message. Note: need the shift lock key down.
keep up the post and I'll try to help.....

[lowrybt1]

So, with a new PSU, I'm finding a signal on U58 pin 8 (oscillator circuit) but it does not match the waveform in the SAMS manual. Also found a signal on pin 39 of the 6502 (clock 02) but also does not match the waveform in SAMS. And no signal to the monitor. Thoughts?

[dave]

Can you post some pictures?

[MK14HAK]

Have you got video and or sync signals at U70 ?? Is the video pot fully clockwise (near U70) ?

[lowrybt1]

I've attached a Google Drive link below. At this point, I've checked all the voltage points listed in the SAMS manual. The one anomaly is that all of the points that should read 4.93 are reading 5.00V. Could that mean anything?

https://drive.google.com/folder/d/0B-u4 ... lPZ1U/edit

[dave]

Hi Tom,

Sounds like power is not the problem. I don't think the 4.93V/5V is an issue.

Since you have no video output, you should concentrate on the video circuit first. Start with the oscillator with the bad waveforms you mentioned earlier. Can you post pictures of the waveforms?

If the oscillator works, then look down the divider chain U30-U59-U60-U61, looking at pins 14,13,12,11 of each an confirm square waves of decreasing frequency (by 1/2) at each pin. If you see an odd waveform, take a picture and post it here.

Good luck!

Dave

[lowrybt1]

Hi Dave,

I've attached a screen shot from my scope. The measures window shows 60 Hz for the frequency. I'm wondering if my settings might be wrong.

Many thanks, Tom