VIC20 purchase from eBay

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mrr19121970
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VIC20 purchase from eBay

Post by mrr19121970 »

I bought on eBay again. I don't need to expand my collection, but was tempted by the seemingly mint condition boxes and polystyrene inlays. The description said:

"This offer contains a VC-20 by Commodore. Several parts missing. Missing items are screws and power supply. For hobbyists." and the pictures showed the mainboards covered with the RF shield.

However, this was abit of a shock...

The 1st one seems to have had it's PSU externalised. Why would you do this? For heat reduction? I assume that I can simply put it all back together.

Image

The 2nd one has the 6502 and all 3 ROMs stolen from it. Not really what I understand from a few missing screws.

Image
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eslapion
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Re: VIC20 purchase from eBay

Post by eslapion »

The 1st one seems to have had it's PSU externalised. Why would you do this? For heat reduction? I assume that I can simply put it all back together.
What a half-ass job!!
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Re: VIC20 purchase from eBay

Post by Boray »

mrr19121970 wrote: The 1st one seems to have had it's PSU externalised. Why would you do this? For heat reduction? I assume that I can simply put it all back together.
I did exactly the same thing with my first Vic-20. Those two parts was put in the Vic-1020 instead. Reason: The rectifier got so hot that it desoldered itself a number of times. I bought a new replacement part and was about to replace it. But instead, I thought this was a better solution. In case I would have to do it again, it would already be outside, plus, all heat now was placed outside the computer. I think the traces on the motherboard also started to get a bit teared up so I probably couldn't replace it more than once.
PRG Starter - a VICE helper / Vic Software (Boray Gammon, SD2IEC music player, Vic Disk Menu, Tribbles, Mega Omega, How Many 8K etc.)
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

I contacted the seller and asked to send me the missing ICs. They seem to think as they added the words "for hobbyists" after mentioning that the screws and psu were missing then this is a blanket get out clause for other missing parts.

Thankfully MCes is able to supply me the roms and a donor 1541 will give me the 6502
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eslapion
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Re: VIC20 purchase from eBay

Post by eslapion »

@mrr19121970
SInce you intend to "put back" the regulator inside the older VIC you got, you could use the opportunity to replace the "heating system" TO-3 regulator with a nice switching regulator which will make the system leaner on power and considerably reduce the heat it produces.
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MCes
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Re: VIC20 purchase from eBay

Post by MCes »

Mmmm.....

for the VIC 20 with PSU externalised:
You haven't the original heatsink, so I suggest to replace the bridge with 4 Schottky diode rectifier (they produce less heat than normal rectifier) type 1N5822 (very cheap..) and replace the regulator with a switching DC-DC converter that have 5A as limit (on ebay: "5A DC-DC adjustable step-down").
Power: 5V * 2.5A = 12.5W
DC-DC converter convert in heat less or more 5..10% of power (0,6...1,3W).

New internal PSU need Pout+Pheatconverter+Prectifier= 15W (less or more) that will be less than 2A at 9Vac (instead of 3A).

Less heat, less power needed!
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." (Albert Einstein)
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

The original heatsink is also there. Still attached to the VR1 and bridge. I will check the components from my PC next week. I didn't even check if the VC20s even work yet.

One result, after I likend the seller's tactics of selling a computer without chips (and not disclosing it) is the same as selling a car without an engine. For a commercial seller a very dubious business practice.

They gave me a partial refund, which covers the cost of MCes roms and enough for a replacement 6502
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MCes
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Re: VIC20 purchase from eBay

Post by MCes »

OK,
if you want to put inside a linear regulator and a bridge rectifier (like as original...) remember that each of this needs a proper heat dissipator: one for bridge, one for regulator


Look: http://sleepingelephant.com/ipw-web/bul ... 915#p83915
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

So the good news is the 1981 chips 2 prong model works out of the box.

The 2nd one with no chips has a strange issue. I assume the cd4066 is duff as the colours are wrong. Instead of blue text I get pink or black. Additionally the screen characters flicker sometimes or weird lines/dots appear.

Image

GORF

Image

DEFENDER

Image

There are 4 MOS ICs onboard:

UD8, UE8 & UF9 : MOS65245

Code: Select all

UD8 and UE8	MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC
  Blank screen.	Partical failure: garbled video or audio. see UB7
UC2 : MOS 8713

Code: Select all

UC2		74LS04		LOGIC
  Screen character colors incorrect (scrambled). If very bad, entire 
screen becomes garbled with flashing characters, vertical bars and 
random colors.
The VIC20 PAL diagnosis cart doesn't seem to run at all. The VIC20 NTSC card checks ZERO PAGE=OK and STACK PAGE=OK and then freezes (displays nothing more, and screen corruption ends)

Any external memory simply is a black screen.
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

So I desoldered the U2 and popped it in the IC tester = NOT FOUND. Soldered in a 14P socket and 74LS04. Now the VC20 is back to life, I even have keyboard functionality (I didn't mention lack of it before as I didn't consider this to be related).

Still the colours are wrong, but passes all tests on the VIC20 diagnosis cartridge. I have black, white, purple and green only (RED->BLACK, CYAN->WHITE, BLUE->PURPLE & YELLOW->GREEN).

Not sure what to replace next CD4066 or UE1, Mike would know, and hopefully can explain this:
Mike wrote:We should have tried to rule out a faulty 2114 by reading back from it (with "AND 15", of course).
Last edited by mrr19121970 on Tue Aug 23, 2016 5:46 am, edited 1 time in total.
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

Well I desoldered the CD4066 and it proved good on the IC tester (and test machine) so proceeded with UE1 2114 which also proved good on a test machine. Tried replacing 6561-101 too and still the same results.

Update

All background and border colours are available.
buzbard wrote:More specifically:

POKE36879,(BG*16)+BC+8

BG = BackGround Color (0 to 15)
BC = Border Color (0 to 7)

The color codes are:
0=Black
1=White
2=Red
3=Cyan
4=Purple
5=Green
6=Blue
7=Yellow
8=Orange
9=Light Orange
10=Pink
11=Light Cyan
12=Light Purple
13=Light Green
14=Light Blue
15=Light Yellow
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

Typing ?PEEK(646) gives the following results:

Code: Select all

BLK (BLACK shown)  : 0 : BIN 0000
WHT (WHITE shown)  : 1 : BIN 0001
RED (BLACK shown)  : 2 : BIN 0010
CYN (WHITE shown)  : 3 : BIN 0011
PUR (PURPLE shown) : 4 : BIN 0100
GRN (GREEN shown)  : 5 : BIN 0101
BLU (PURPLE shown) : 6 : BIN 0110
YEL (GREEN shown)  : 7 : BIN 0111
So the 2nd bit is not being taken into account

I measured FB13 which connecs UC2 pin 8 with UD1 pin 5,6,12&13 and receive the correct pattern

Image
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

MC71@forum64.de told me that UE1 pin12 and UB7 Pin7 must have a break. I tested with my continuity meter. Seemed OK to me, however a hack brought the baby back to life.

Image

Image
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mrr19121970
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

Ok, fully resolved now. The original socket is a single leaf. Bending VIC-I pin7 in abit made contact better. I will replace the socket.
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Re: VIC20 purchase from eBay

Post by mrr19121970 »

Good info here

6561 PIN CONFIGURATION

Code: Select all

                          ___________________
                         |                   |
               not used -|1                40|- +5V
                         |                   |
       Composite colour -|2                39|- Clock-in phase-1
                         |                   |
      Sync. & luminance -|3                38|- Clock-in phase-2
                         |                   |
             READ/WRITE -|4                37|- Light pen
                         |                   |
                   VD11 -|5                36|- Clock-out. Not used.
                         |                   |
                   VD10 -|6                35|- Clock-out phase-1
                         |                   |     
                    VD9 -|7                34|- A13
                         |                   |
                    VD8 -|8                33|- A12
                         |                   |
                     D7 -|9                32|- A11
                         |                   |
                     D6 -|10               31|- A10
                         |                   |
                     D5 -|11               30|- A9
                         |                   |
                     D4 -|12               29|- A8
                         |                   |
                     D3 -|13               28|- A7
                         |                   |
                     D2 -|14               27|- A6
                         |                   |
                     D1 -|15               26|- A5
                         |                   |
                     D0 -|16               25|- A4                            
                         |                   |
                  POT X -|17               24|- A3 
                         |                   |      
                  POT Y -|18               23|- A2 
                         |                   |
        Composite sound -|19               22|- A1 
                         |                   |     
                    GND -|20               21|- A0 
                         |___________________|

Code: Select all

 Pin 1: Not connected.
 Pin 2: The composite colour line of the video output.
 Pin 3: The syncronisation and luminance line of the video output.
 Pin 4: The video read/write line that is at logic 1 when data is being read
        from the colour or video RAM.
 Pins 5-8: The lines of the special colour data bus.
 Pins 9-16: The eight lines of the ordinary data bus.
 Pin 17: The input line for potentiometer X.
 Pin 18: The input line for potentiometer Y.
 Pin 19: The composite sound line of the audio output.
 Pin 20: GND
 Pins 21-34: The 14 address lines of the VIC.
 Pin 35. The clock-out line that becomes the external time base for the
         6502A microprocessor.
 Pin 36: The system phase-2 clock-out line. Not connected.
 Pin 37: Light pen input line.
 Pin 38: Clock-in line from the master clock - phase-2 time.
 Pin 39: Clock-in line from the master clock - phase-1 time.
 Pin 40: +5V.

Code: Select all

 The colours and their representations are:

   BLACK            000
   WHITE            001
   RED              010
   CYAN             011
   PURPLE           100
   GREEN            101
   BLUE             110
   YELLOW           111

 The fourth bit (bit 3) of each location is used to indicate if multicolour
is to be used (discussed later).
 It is interesting to note that the VIC has a special four line data bus that
links the colour RAM to the VIC itself that is used solely to convey the 
colour data to the VIC.
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