White screen commodore 64

[kyokorn]

Hello guys, 

 

I bought my first commodore 64, sadly is not working, so far i did the follow test:

 

* Voltage OK on the PSU (11 VAC and 4.92 VCD)

* Pla Chip OK (tested with my TL866 II Plus)

* Rom chip OK (reading the info with TL866)

* LS257 OK (tested with TL866)

 

The issue is the screen is on wthite, with RF connection is not working neither

 

Any advise what can be the issue?

 

Thanks in advance!

LB

 

 

[+OLD CS1]

Are the artifacts (rough edge and purple and green coloring) on the right part of the video display?  My first guess points be toward the VIC-II area, either itself or something with timing.

[CAJoeG]

Check this site for a photo that matches your C64's issue the closest: https://www.pictorial64.com/

 

If it's more gray than white, it's likely the VIC-II chip. Which would also explain why the RF connection doesn't work either.

https://www.pictorial64.com/fault.htm?id=u19_24

 

If you know someone with a Chip Tester Pro V2, they can test the chip for you.

 

Replacement VIC-II chips are hard to find. But one of these FPGA replacements will work great. I have one (mini):

https://videogameperfection.com/products/vic-ii-kawari/

 

Good luck!

 

Joe

 

 

[kyokorn]

Hello guys

 

Yes, after change the VIC II chip, at least now i Have a video (without letters =P)

 

 

 

Apparently the ROM chip is ok, I did a DIP converter to load the information with my programmer TL866, comparing the bin looks good, what you think ? is a problem maybe with one of the RAM chip? 

 

Already i requested a pcb to build the test cartige, 

 

BR / LB 

Edited August 23 by kyokorn

[+OLD CS1]

On 8/23/2024 at 1:12 AM, kyokorn said:

 

What projector are you using?

[hofster]

Which ROM chip is ok? There are two or three ROMs in a C64.

This looks like a typical Basic ROM problem but it doesn't have to be.

[+OLD CS1]

1 hour ago, hofster said:

Which ROM chip is ok? There are two or three ROMs in a C64.

This looks like a typical Basic ROM problem but it doesn't have to be.

If it is the BASIC ROM at fault, a game cartridge should prove that out as BASIC is bypassed.

[kyokorn]

On 8/24/2024 at 4:59 PM, OLD CS1 said:

What projector are you using?

Hello friend, is a little old LG 

https://www.lg.com/us/home-video/lg-PB60G-micro-portable 

[+OLD CS1]

4 minutes ago, kyokorn said:

Hello friend, is a little old LG 

https://www.lg.com/us/home-video/lg-PB60G-micro-portable 

Nice.  I am impressed with its output.

[kyokorn]

On 8/25/2024 at 11:42 AM, OLD CS1 said:

If it is the BASIC ROM at fault, a game cartridge should prove that out as BASIC is bypassed.

You right!

 

Yesterday finally arrive the pcb to build a Dead test cartige, but was very sad  One flash on the screen (bad ram), I disoldered all the RAMs and i did the most stupid novice error, 

 

Building a circuit to test the memmory (with an Arduino nano), i just connect the rams on the wrong direction  the most strange was on the arduino pass all the test xD

 

https://ezcontents.org/4164-dynamic-ram-arduino

 

then i connect on the right way the memmories, all of them have error  (Is very logic because on the wrong way was connected Vcc to GND and GND to Vcc☠️)

 

I have 2 questions for you guys that have more expierence.

 

* The memmories that are avaialable to buy on Aliexpress should be work? For example this one

https://es.aliexpress.com/item/33042258541.html?spm=a2g0o.order_list.order_list_main.5.4887194dHfsXTF&gatewayAdapt=glo2esp

 

* The test on arduino is very accuarate? You tried before? or you have a better suggestion to test the ram memmories? 

 

Many thanks in advance!

LB

 

 

 

Edited August 28 by kyokorn

[hofster]

I don't know how accurate that Arduino DRAM tester is but at least it can tell which chips are dead if any.

 

Those AliExpress chips will mostly work. My experience is the same as in the comments. They come poorly packaged with cling film in a plastic envelope and at least 20% of the chips are already dead. Many of them have mangled pins and some may even miss a pin or two.

All of them have been repainted with some bogus marking so you have no idea knowing what brand, model and speed they really are. Not that speed matters much in a C64 but they may even be MT4264's that has been rebranded as 4164's and you don't want MT chips because they are more prone to failure.

With all that said, you can definitely repair your C64 using those AliExpress chips but I recommend that you buy a bunch of extra chips.

Remember to install sockets!

 

[kyokorn]

55 minutes ago, hofster said:

I don't know how accurate that Arduino DRAM tester is but at least it can tell which chips are dead if any.

 

Those AliExpress chips will mostly work. My experience is the same as in the comments. They come poorly packaged with cling film in a plastic envelope and at least 20% of the chips are already dead. Many of them have mangled pins and some may even miss a pin or two.

All of them have been repainted with some bogus marking so you have no idea knowing what brand, model and speed they really are. Not that speed matters much in a C64 but they may even be MT4264's that has been rebranded as 4164's and you don't want MT chips because they are more prone to failure.

With all that said, you can definitely repair your C64 using those AliExpress chips but I recommend that you buy a bunch of extra chips.

Remember to install sockets!

 

Appreiciate the comments friend, 

 

I will try then!

 

Thanks!