Author Topic: C-64 Weirdness.  (Read 2303 times)

0 Members and 1 Guest are viewing this topic.

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
C-64 Weirdness.
« on: January 16, 2019, 07:23:48 am »
Guys and Gals i am having quite a strange issue with one of my C-64 Motherboards.

Datasette do not function reason being a missing 6.9 volt line (From 9Volt DC)

Replaced..

Q1 CR1 R1

Q2 R3 Seem fine.

9 volt unregulated is present Q1 Collector and R1 top

No Signal from R1 to base to base

Same issue with R3 +3 present from U6 to the resistor but no signal from resistor to Q3 base.

Resistors are fine Transistors are fine Diode is fine.

While locating reasons for error i noticed if i remove U7 VIC the circuit all the sudden works perfectly but not if VIC is present.. Question is why ?
I see no reason why it would effect the circuit the way it does.

Any tips would be welcome.

Schematic





 

Offline CJay

  • Super Contributor
  • ***
  • Posts: 3547
  • Country: gb
Re: C-64 Weirdness.
« Reply #1 on: January 16, 2019, 09:39:26 am »
You've got the right VIC chip haven't you?

ISTR there were later versions for 5V only, early versions used '12V' on pin 13, late versions used 5V and if you plug in the wrong one it could do funny things to the cassette as the cassette power is from the same rail.
 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #2 on: January 16, 2019, 10:53:42 am »
No, it's the other way around.

"In all C64 models VIC-II is socketed for easy replacement, but it is important to notice that 6569, 6572, 6573, 6566 and 6567 use 12 volts and 5 volts when 8565 and 8562 use only 5 volts. Replacing old version with new version without motherboard modification destroys 8565 and 8562 if powered up in the oldest versions of C64 motherboards."

Best is to measure Pin 40 to ascertain the voltage present there and determine the model.
 

Offline CJay

  • Super Contributor
  • ***
  • Posts: 3547
  • Country: gb
Re: C-64 Weirdness.
« Reply #3 on: January 16, 2019, 11:39:23 am »
No, it's the other way around.

"In all C64 models VIC-II is socketed for easy replacement, but it is important to notice that 6569, 6572, 6573, 6566 and 6567 use 12 volts and 5 volts when 8565 and 8562 use only 5 volts. Replacing old version with new version without motherboard modification destroys 8565 and 8562 if powered up in the oldest versions of C64 motherboards."

Best is to measure Pin 40 to ascertain the voltage present there and determine the model.

Umm, I thought that was what I said?
 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #4 on: January 16, 2019, 11:56:34 am »
Oh correction, Pin 13 should be the correct pin to measure VDD pin.

Schematic above refers to VIC-II, the 5V version but the mother-board may be the old type, so it's the other way around, 5v type into 12V slot will  damage the VIC chip.
12V type into 5v slot, the chip should survive.

« Last Edit: January 16, 2019, 12:03:55 pm by Armadillo »
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #5 on: January 16, 2019, 09:31:20 pm »
The board is 250469 what uses 9 volt only for SID and power Cassette drive and some other ports
The VIC is VIC 2 8565 tested with two VIC2's both produce same problem.

Mystery is what can pull the voltages down on those points.. I understand the 9 volt zener combo (to reduce the voltage to 6.8 volts for the cassette drive but what is the 3.3 volt combo coming from the other direction.

And how can removing the VIC fix the problem.  |O

 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #6 on: January 16, 2019, 09:42:36 pm »
Just Remove Q2 and test it again.
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #7 on: January 16, 2019, 09:55:07 pm »
I will try.
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #8 on: January 16, 2019, 10:36:52 pm »
Just Remove Q2 and test it again.

I removed Q2 and the cirquit worked as intended (i got the regulated 6.8 to the cassette power pin)

Problem the computer do not boot after removal of the Q2 (no display nothing)  :wtf:

Put the Q2 pack computer boots but no cassette drive.


 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #9 on: January 16, 2019, 10:47:43 pm »
I asked you to remove Q2 just to ascertain the running codes, obviously there must be starting orders.

Have you component tested Q2?
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #10 on: January 16, 2019, 11:06:32 pm »
I asked you to remove Q2 just to ascertain the running codes, obviously there must be starting orders.

Have you component tested Q2?

Seems test fine but i will order replacement and test.
 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #11 on: January 16, 2019, 11:15:48 pm »
Well, better hope that its from Q2, because the only thing that commands it is from the MPU itself [thru one resistor].

 :D
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #12 on: January 16, 2019, 11:23:32 pm »
Well, better hope that its from Q2, because the only thing that commands it is from the MPU itself [thru one resistor].

 :D

Like i said between mpu and resistor there is 3.3 volt that goes to resistor.
Between resistor and Q2 there is no voltage.

Old resistor reads fine and been replaced.

Only thing i do not undestand is if 3.3 goes to resistor and resistor is fine why there is no 3.3 in the collector base leg..
« Last Edit: January 16, 2019, 11:27:06 pm by Bashstreet »
 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #13 on: January 16, 2019, 11:47:51 pm »
How do I put it to you?

Because your Q2 testing must be very unsure that you didn't find out that the Q2 is shorted from Collector to Emitter or faulty.

EDIT [OF COURSE I ASSUME YOU KNOW HOW TO TYPE "LOAD" AND PRESS THE PLAY BUTTON].

« Last Edit: January 17, 2019, 12:08:13 am by Armadillo »
 

Offline fzabkar

  • Frequent Contributor
  • **
  • Posts: 525
  • Country: au
Re: C-64 Weirdness.
« Reply #14 on: January 16, 2019, 11:53:15 pm »
The MPU outputs 3.3V to Q2 via base resistor R3. The BE voltage should now be around 0.6V - 0.7V. This turns Q2 on, in which case its CE voltage would drop to around 0.2V. This in turn removes the base drive from Q1, thereby turning it off.

So there is nothing wrong in this area. Instead I suspect that the VIC chip may be dragging down one or more of the bus pins. Do you have a spare VIC?
 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #15 on: January 16, 2019, 11:57:27 pm »
Read #8
 

Offline fzabkar

  • Frequent Contributor
  • **
  • Posts: 525
  • Country: au
Re: C-64 Weirdness.
« Reply #16 on: January 17, 2019, 12:21:48 am »
That post is confusing. Removing Q2 allows Q1 to turn on (because Q2 is no longer robbing Q1 of its base drive), so it is to be expected that a 6.2V supply (= 6.8V Zener - 0.6V BE) would be present at the cassette interface. However, the absence of Q2 should not prevent the C64 from booting, AFAICT.
« Last Edit: January 17, 2019, 12:23:37 am by fzabkar »
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #17 on: January 17, 2019, 12:27:36 am »
That post is confusing. Removing Q2 allows Q1 to turn on (because Q2 is no longer robbing Q1 of its base drive), so it is to be expected that a 6.2V supply (= 6.8V Zener - 0.6V BE) would be present at the cassette interface. However, the absence of Q2 should not prevent the C64 from booting, AFAICT.

That's right. It is all very weird.

Something fubar is going on .

 

Offline Armadillo

  • Super Contributor
  • ***
  • Posts: 1725
  • Country: 00
Re: C-64 Weirdness.
« Reply #18 on: January 17, 2019, 12:37:09 am »
Because it was flagged/interrupted that serial data in coming in and hang there waiting since it was never intended or at least planned for Q2 to be out of circuit.!
it's added complexity enough, because "seems" like working is not a test result of Q2 in the first place.

Anyway, make sure you press the play button...... otherwise it will be so funny or making at least make sure that the status did pull low for play.

OK, is enough for me.

That post is confusing.
« Last Edit: January 17, 2019, 12:46:24 am by Armadillo »
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #20 on: January 17, 2019, 02:32:59 am »
I tested the transistor again it seems totally fine..  :-//

Maybe something else is fubar
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #21 on: January 17, 2019, 02:35:04 am »
The MPU outputs 3.3V to Q2 via base resistor R3. The BE voltage should now be around 0.6V - 0.7V. This turns Q2 on, in which case its CE voltage would drop to around 0.2V. This in turn removes the base drive from Q1, thereby turning it off.

So there is nothing wrong in this area. Instead I suspect that the VIC chip may be dragging down one or more of the bus pins. Do you have a spare VIC?

Yes i have a spare VIC same symptoms. I suppose my both VIC's could be broken but they function otherwise totally fine if they are  :-//
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #22 on: January 17, 2019, 02:39:27 am »
I considered this earlier also but i am not sure how to check if some of lines are being dragged down.
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #23 on: January 17, 2019, 02:42:20 am »
« Last Edit: January 17, 2019, 02:45:01 am by Bashstreet »
 

Offline Bashstreet

  • Frequent Contributor
  • **
  • Posts: 298
  • Country: gb
Re: C-64 Weirdness.
« Reply #24 on: January 17, 2019, 02:53:12 am »
The MPU outputs 3.3V to Q2 via base resistor R3. The BE voltage should now be around 0.6V - 0.7V. This turns Q2 on, in which case its CE voltage would drop to around 0.2V. This in turn removes the base drive from Q1, thereby turning it off.

So there is nothing wrong in this area. Instead I suspect that the VIC chip may be dragging down one or more of the bus pins. Do you have a spare VIC?

Yes i have a spare VIC same symptoms. I suppose my both VIC's could be broken but they function otherwise totally fine if they are  :-//

Also if this is how the circuit is supposed to work why when i insert the cassette drive it gets no power what should then trigger the power on ?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf