Memory Expanssion questions

[grondinm]

Hello,

I am very new to the VIC-20 world just got mine this week. (Pics cause i'm excited to have this) I also got one of these with it

https://www.nightfallcrew.com/18/05/201 ... re-vic-20/

Just to give me more RAM until i can afford to get a Penultimate+. Trouble is when i put it in my vic and have the switches in the 1A 2B positions i don't seem to be getting the full 16k expansion. My VIC tells me it has 9918 bytes available. That seems like an odd number even to me with my limited understanding...

I understand very little about memory maps in general but from what i gather memory available for BASIC needs to be contiguous and since this cart says it's adding to blocks 1&2 i figured i should have access to all of it. Or a number that makes more sense that 9918...

What am i missing here? Is it hardware related? How can i diagnose?

Thank you

[16KVIC20]

Sounds like you're only getting about 8K.

With 16K expansion you should see 19697 Bytes free.
Have you tried different combinations of switch positions, do you definitely have the correct combination?

If so, maybe you have a dud chip in the RAM pack, or maybe there could be a dud trace on the connector on the cartridge, or a dud slot in the VIC 20.
I'm no expert, and could be wrong, but they seem possible places to start from.

I've never had switched expansions like this, only ever fixed, and nearly always 16K, as my name would suggest! I think it's the sweet spot for a VIC 20.

[grondinm]

Thanks for the reply.

Based on the "documentation" at the site i posted above the switches in this position should get me the full 16k. I have tried other positions and got around 3k then nothing. So i think it's looking like a bad chip(or trace or something) on the expansion cart. Might open it up and see if anything look obviously wrong.

[MCes]

With VIC 20 switched off: insert 5..10 times the cartridge,
because years can made oxide the cartridge contacts (on cartridge, but also on connector)

[grondinm]

With VIC 20 switched off: insert 5..10 times the cartridge,
because years can made oxide the cartridge contacts (on cartridge, but also on connector)

That did not seem to help but thanks for the suggestion. The few other cartridges i got with the system seem to work fine so i don't suspect the port on the VIC at this point.

[Vic20-Ian]

You should see one of the following Bytes free messages:

3583
6655
11775
19967

If you see something else then either a connection is not working or a memory chip has failed.

As there is little to lose I would try light removal of oxide on the pins with a piece of nylon pan scrubber.

Rub gently on both sides of the pins on the cartridge a few times and give it another try.

Good luck

[16KVIC20]

And just count yourself lucky it's a VIC 20 not a ZX Spectrum. They are prone to getting crud on their edge connector, which can be tricky to shift.

[grondinm]

You should see one of the following Bytes free messages:

3583
6655
11775
19967

If you see something else then either a connection is not working or a memory chip has failed.

As there is little to lose I would try light removal of oxide on the pins with a piece of nylon pan scrubber.

Rub gently on both sides of the pins on the cartridge a few times and give it another try.

Good luck

Thank you.

I tried the rubbing with nylon pan scrubber and that did not seem to help. Maybe i did not rub hard enough but i did not want to make it worse.

So i am able to get 6655 and everything seems to work fine in that mode. If i try anything else i end up with 9918 and things act up. Random out of memory errors and things. So i'm gonna chalk it up to one or multiple bad chips or traces or what have you. At least this cart did not cost me much and even the extra 3k will allow me to play a few different games. Soon(ish) i'm gonna get the Penultimate+ anyways. Altho is there other maybe less expensive ram expansion carts i could get. Did not seem to find much on ebay(did not look very hard tho...)

[Vic20-Ian]

https://www.ebay.co.uk/sch/i.html?_from ... k&_sacat=0

Lots under £20 on Ebay.

[MCes]

From a forum member ... (I!)
viewtopic.php?f=3&t=9802

[grondinm]

From a forum member ... (I!)
viewtopic.php?f=3&t=9802

Very much interested in this. Sent you a PM.