Vic20 Vixen Switchable 16k RAM Expansion Repair

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siccoyote
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Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby siccoyote » Sun Nov 26, 2017 6:47 pm

I have had the Vixen Expansion on my shelf unused for 20 years.

I decided to play with my Vic 20 so I plugged it in and noticed it gave me all the memory it should, great!

Then after playing for a couple of days I put it back in the box and waited a week to get an SD2IEC, I was glad I'd be able to play everything up to 16k.

But when I had it plugged in and loaded up with the SD2IEC connected, 3.5k. !!! turn off unplug, plug in again. 3.5k !!!

I don't know what happened it just now doesn't react at all to it being plugged in.

Could it be that using it after all this time killed off some component?

Image

I am considering replacing the capacitors as I always hear with old electronics it's best to do that.

Any advice would be most welcome.

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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby eslapion » Sun Nov 26, 2017 7:03 pm

This board is not is a case so it is exposed to static electricity. You probably damaged one of the DRAM just handling it.

I will fix it for you. PM sent!
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siccoyote
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby siccoyote » Sun Nov 26, 2017 7:11 pm

It was in a case, I just took it out now to examine it and am very careful when handling only touching the corners, also this isn't a very staticy environment :)

I have got a low end qualification in electronics so I am aware of the problems that can happen.

Unfortunatly I would think sending it from me in the UK to you in Canada and back again would cost a similar amount to buying a new one from ebay.
Thankyou for your offer, if you could offer any hints I could carry out I'd be most greatful.

EDIT: Just seen your pm, I will reply there.

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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby eslapion » Sun Nov 26, 2017 7:28 pm

This is great! This RAM expansion seems to use only standard discreet logic 74_XX chips and a pair of 16k x 4bit DRAM chips which makes it very easy to reproduce or fix.

I will document the schematics and get it posted online.
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norm8332
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby norm8332 » Sun Nov 26, 2017 9:07 pm

I see corrosion on the contacts, have you tried cleaning the contacts?

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orion70
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby orion70 » Mon Nov 27, 2017 12:18 am

Yep I guess a bit of alcohol would do. I resuscitated a lot of old carts that way.

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Mayhem
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby Mayhem » Mon Nov 27, 2017 6:16 am

I own the Vixen myself, still works great, very good back in the day memory expansion, in lieu of modern equivalents such as Megacart or Penultimate Expansion. As you could have 0k, 3k, 8k and 16k all off the same setup. May try to open mine to compare and spot if anything is amiss heh.
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby eslapion » Mon Nov 27, 2017 7:36 am

norm8332 wrote:I see corrosion on the contacts, have you tried cleaning the contacts?

Pure alcohol and a white eraser can do wonders.
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lance.ewing
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby lance.ewing » Wed Nov 29, 2017 3:09 pm

Mayhem wrote:I own the Vixen myself, still works great, very good back in the day memory expansion, in lieu of modern equivalents such as Megacart or Penultimate Expansion. As you could have 0k, 3k, 8k and 16k all off the same setup. May try to open mine to compare and spot if anything is amiss heh.

The Vixen sounds similar to a custom cartridge that my Dad built back in the day (mid 80s). It had a switch on the back with three positions: 0K, 3K, and 24K. I forget sometimes that other people might not have had something like that with switchable memory configurations back in those days.

siccoyote
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby siccoyote » Wed Nov 29, 2017 11:33 pm

Well I would be tempted to try out cleaning it and stuff, but eslapion seems quite happy to get his hands on it, so got it in a box now.

Though if it could be modified so it's 32k I wouldn't mind :)

That would make it able to play about 3 more games right?

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Mike
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby Mike » Thu Nov 30, 2017 3:08 am

siccoyote wrote:That would make it able to play about 3 more games right?

If you only go by what's available at ftp.zimmers.net, yes.

However, that's not the last word on this (see here), and VIC Doom requires +35K RAM (i.e. an extra +3K RAM expansion alongside your possibly enhanced +16K -> +32K RAM expander), so "just" +32K are still not sufficient in some cases. :twisted:

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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby eslapion » Thu Nov 30, 2017 3:53 am

siccoyote wrote:Though if it could be modified so it's 32k I wouldn't mind :)

Most static RAM based expansions can be increased by either piggybacking extra ICs on top of those present or using empty sockets.

See: http://sleepingelephant.com/denial/wiki ... 2k_mod.jpg

However, the more complex accessing scheme of DRAM used in the Vixen might make this a lot more complex, perhaps impossible.

That would make it able to play about 3 more games right?

A lot of games and software using 24k or more has appeared during the last 5 years.
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Mayhem
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby Mayhem » Thu Nov 30, 2017 7:59 am

The thing with Vixen is, there's only two binary switches, so that's why the memory options are 0, 3, 8 and 16. You'd need to sacrifice one of those options to allow for 24k or 35k in there.
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Mike
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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby Mike » Thu Nov 30, 2017 12:48 pm

Mayhem wrote:The thing with Vixen is, there's only two binary switches, so that's why the memory options are 0, 3, 8 and 16. You'd need to sacrifice one of those options to allow for 24k or 35k in there.

Everything that requires +8K should also run with +16K, +24K and +32K (the latter with 8K in BLK5). Likewise, everything which requires +16K should also run with +24K and +32K. See also here: "RAM... what to get?". In practice, a RAM expander with the four settings: 0K, +3K, +32K and +35K is all you'd need *) - barring any extra RAM in I/O space - incidentally, that's exactly what Mega-Cart provides. And those four cases *can* be encoded with 2 DIP switches. ;)

I strongly suspect though, that the access and refresh logic on the Vixen Card only supports two 16Kx4 DRAMs. It would need a complete re-design to add further RAM. Another DRAM based card discussed elsewhere here *does* have two open places to add another two 4416 DRAMs which would then indeed provide +32K RAM in total.



*) you could even provide +35K RAM fixed, and just set the limits for BASIC and the position of screen RAM according to the known values to simulate all other kinds of RAM expanders - or for that matter, an unexpanded VIC-20. The boot loader in my Unexpanded Type-In Collection does this to save the user the trouble of plugging the RAM expansion in and out.

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Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Postby MCes » Fri Dec 01, 2017 2:59 pm

ok,
it will be "advertisement", but....

http://sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?f=3&t=8582

Image

up to 37k selectable , I/O area fillable with RAM (useful for storing loader as SJLoad, or RABBIT), and BLK 5 can be write protected....
“Don’t argue with idiots because they will drag you down to their level and then beat you with experience” (Mark Twain ?)


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