View Profile: dave_m - Vintage Computer Forum

October 23rd, 2020, 10:54 AM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

With three chip selects in the PIA, it may too difficult to get a good trigger to check the data lines using the scope. Let us ponder on other tests.

47 replies | 1374 view(s)

October 22nd, 2020, 01:35 PM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

Signals looks OK to the PIA, the chip selects are connected properly to the PIA. The 50 Hz is not there because CRT Controller (6545) is not...

47 replies | 1374 view(s)

October 22nd, 2020, 10:44 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

Hutch, Please tell us more about the equipment you used to find the problem. I don't have a digital scope, but you say the one you used had a VGA...

76 replies | 2245 view(s)

October 22nd, 2020, 07:45 AM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

The UB12 PIA that handles the keyboard and interrupt is in the range of $E810. It requires /SEL E Low, X8XX High, and address line A4 high. ...

47 replies | 1374 view(s)

October 21st, 2020, 08:54 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

OK, I was thinking that there was a bad solder joint between C6-pin11 and C7-pin1 causing the line to float and making C7 pin3 to toggle at the clock...

76 replies | 2245 view(s)

October 21st, 2020, 08:12 PM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

Yes, it looks fine. I was hoping a chip select problem at the ROM(UD7) was stepping on the PIA and keeping it from being properly initialized and...

47 replies | 1374 view(s)

October 20th, 2020, 06:49 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

Yes, J=0, K=1 then Q is Low at next clock. Look right at C7 pin 1, the J input. Is it high or floating (2.6V) when its source C6 pin 11 is Low?...

76 replies | 2245 view(s)

October 20th, 2020, 04:22 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

You are not paying attention. C7 pin 1 (J input) is supposed be connected to C6 pin 11 which you say is Low. Therefore the output of the F/F can not...

76 replies | 2245 view(s)

October 20th, 2020, 01:31 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

From this it seems that the J input at C7 pin1 is going open. Reflow the solder joint.

76 replies | 2245 view(s)

October 20th, 2020, 09:04 AM

MikeS replied to a thread Commodore 900 restoration in Commodore

Floppy disks are floppy disks; it might be possible to archive those somehow, even if only flux transitions for analysis later. What make/model is...

5 replies | 124 view(s)

October 11th, 2020, 08:30 AM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

The photos of your message #20 showing the chip selects did not attach properly and could not be seen. I assumed they were OK, but we need to see...

47 replies | 1374 view(s)

October 8th, 2020, 07:22 AM

MikeS replied to a thread Turbo/Speed LED Display help needed. in Vintage Computer Hardware

eswan summed it up pretty well. Have a look here for some examples; at a fast look none match yours exactly but one of the two-digit ones may be...

2 replies | 129 view(s)

October 5th, 2020, 11:49 AM

dave_m replied to a thread PETE 8032 Monitor - Vertical/Horizontal Size Adjustment in Commodore

I don't think it is possible to change the title.

11 replies | 385 view(s)

October 4th, 2020, 09:50 AM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

If you have a scope, check for the 50 Hz interrupt before and after.

47 replies | 1374 view(s)

October 4th, 2020, 09:49 AM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

You might want to just cut the IRQ line at pin 21 of the VIA. I don't think it is used. After checking for proper operation, you can tack it back in...

47 replies | 1374 view(s)

October 4th, 2020, 06:35 AM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

The keyboard PIA UB12 is the only chip that issues an interrupt. The Vertical Drive signal goes to a UB12 input at pin 18. The PIA is initialized to...

47 replies | 1374 view(s)

October 3rd, 2020, 10:55 PM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

The keyboard is not needed for the cursor. You may not yet be getting the 60 Hz interrupt. A Motorola 6820 or 6821 may be easier to find than a 6520.

47 replies | 1374 view(s)

October 3rd, 2020, 03:11 PM

dave_m replied to a thread Faulty 8032-SK with no V-Sync - Gary in Commodore

Good work so far. Are you getting a blinking cursor proper keyboard response?

47 replies | 1374 view(s)

October 2nd, 2020, 01:15 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

OK, now I understand. Your screen only goes out once in a while and is mostly good. That is tricky to troubleshoot.

76 replies | 2245 view(s)

October 2nd, 2020, 08:32 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

So you have a good Vertical Sync most of the time? The Vertical Sync will be a about a two mS negative pulse every 16.66 mS (60 Hz). If you don't...

76 replies | 2245 view(s)

October 1st, 2020, 02:35 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

Hi Hutch, You don't see C7-pin 3 pulse because it goes low (and stays low) when the State Sequencer stops/hangs as it is the clock to the state...

76 replies | 2245 view(s)

October 1st, 2020, 10:25 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

Andy, Yes it could as it might keep the main counters D6 and D7 from reaching the terminal count (detected by D8-pin3) to increment the sequencer. ...

76 replies | 2245 view(s)

September 30th, 2020, 07:46 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

A1-pin2 (Reset) must be LOW to allow the counter to run. If it is pulsing high a lot then the counter will stay reset. If pin 2 is LOW most of the...

76 replies | 2245 view(s)

September 30th, 2020, 04:19 PM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

No, there is little circuitry in common between HSync and VSync. VSync is the output of a complicated sequencer and HSync is an output a simple...

76 replies | 2245 view(s)

September 28th, 2020, 09:37 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

A little confusing, but not a problem. It is shown as a 'demorgan' of a NAND gate and is equal. Actually shown for clarity as this gate is used in...

76 replies | 2245 view(s)

September 28th, 2020, 08:40 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

If the B6 outputs were going at that rate, you would see a vertical sync pulse every 16 uS instead of about 16 mS. The screen would definitely have...

76 replies | 2245 view(s)

September 28th, 2020, 08:30 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

Hutch, But then you said you COULD see the compliment signal out of C7- pin 2?? That should just look like a negative glitch compared to the...

76 replies | 2245 view(s)

September 28th, 2020, 08:25 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

OK, then your problem is the scope. The pulse width of the clocks out of C7 are only 0.5 uS wide and you apparently can't see them.

76 replies | 2245 view(s)

September 28th, 2020, 08:06 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

I have witnessed PET owners work for a month to fix a problem with this sequencer because when it is stuck, it is difficult to see what is wrong as...

76 replies | 2245 view(s)

September 28th, 2020, 08:00 AM

dave_m replied to a thread PET 9" Monitor, losing vertical deflection randomly in Commodore

Hi Daver, I think he is saying he sees no clock when the 'screen collapses'. When the sequencer is working, the C7 pin 3 output will generate a...

76 replies | 2245 view(s)

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