What is wrong?

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By Grauw

Ascended (10581)

Grauw's picture

07-04-2018, 23:11

RAM chips can go bad, it just happens. You’re lucky that this problem is one of the easiest to diagnose.

If you can’t replace the chip yourself, find your local retro computer club or electronics guy or repair shop and ask them if they can do it for you. Anyone who can handle a soldering iron really. Maybe they have one themselves, but otherwise you can order 4116 RAM chips on eBay.

By the way, I think the problematic one is U32, since the TMS9918 manual says RD0 is the MSB and RD7 is the LSB. Otherwise it’s U37, but try to replace U32 first.

By MSX_Dan

Supporter (12)

MSX_Dan's picture

07-04-2018, 23:11

can any 4116 ram be used because i cannot find any on ebay uk with the same number etc on.

By Grauw

Ascended (10581)

Grauw's picture

07-04-2018, 23:14

It needs to look like the chips with the markings U31-U38 in the bottom right of this pic:

If it then says 4116 on top you’re probably good :).

By MSX_Dan

Supporter (12)

MSX_Dan's picture

07-04-2018, 23:16

i could only find 416p-3 chips.

By Grauw

Ascended (10581)

Grauw's picture

07-04-2018, 23:27

https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=4116+ram&_s...

https://www.ebay.co.uk/itm/8pcs-new-old-stock-4116-lower-ram...
https://www.ebay.co.uk/itm/TMS411615NL-4116-RAM-for-Sinclair...

Etc.

Though if they’re not of exactly the same type, perhaps best to replace all eight of them at once. The one on the board seem to be 200 ns ones (4116-2/20), the one on the first listing too, and the one on the second are 150 ns (bit faster). Not sure about that. It’s probably ok though. The first listing also says that you can combine different brands and types on ZX Spectrum, for MSX it’s probably the same.

By Grauw

Ascended (10581)

Grauw's picture

07-04-2018, 23:34

The ZX Spectrum also uses this type of chips, so if you know a Spectrum repair guy (I guess more common in the UK) he can also fix it for you and will probably have the chips in stock.

By Alexey

Guardian (3385)

Alexey's picture

01-07-2018, 05:11

MSX_Dan, did you fix your Canon MSX? Seems that my own Canon died today:

Quick diagnostics with a grounded wire and Data Out pin shows that U32 is dead. Will put a socket onto the board and try with a working 4116 chip. I wonder whether this is just a coincidence that in 2 different machines the same VRAM chip died...

By Alexey

Guardian (3385)

Alexey's picture

01-07-2018, 13:10

Yep, U32 was faulty. The diagnostics works well with the single wire. Smile The machine is back in service...

By OmaiGodman

Resident (59)

OmaiGodman's picture

02-07-2018, 11:36

Alexey wrote:

Quick diagnostics with a grounded wire and Data Out pin shows that U32 is dead. Will put a socket onto the board and try with a working 4116 chip. I wonder whether this is just a coincidence that in 2 different machines the same VRAM chip died...

MSX machines have quantum mechanics? Who would have thought they'd be so ahead of their time oO

By Philip

Champion (380)

Philip's picture

02-07-2018, 23:33

So how do you diagnose with a grounded wire?
I get how to diagnose with a logic probe, but as I'm pretty new to hardware this sounds somewhat weird to me Tongue

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