Vic20 Vixen Switchable 16k RAM Expansion Repair

Modding and Technical Issues

Moderator: Moderators

Post Reply
siccoyote
Vic 20 Dabbler
Posts: 91
Joined: Sun Nov 26, 2017 6:27 pm
Location: UK

Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by siccoyote »

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.
User avatar
eslapion
ultimate expander
Posts: 5458
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by eslapion »

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!
Be normal.
siccoyote
Vic 20 Dabbler
Posts: 91
Joined: Sun Nov 26, 2017 6:27 pm
Location: UK

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by siccoyote »

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.
User avatar
eslapion
ultimate expander
Posts: 5458
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by eslapion »

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.
Be normal.
norm8332
Vic 20 Nerd
Posts: 626
Joined: Sun Nov 13, 2016 11:04 am
Location: USA

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by norm8332 »

I see corrosion on the contacts, have you tried cleaning the contacts?
“In religion and politics people’s beliefs and convictions are in almost every case gotten at second-hand, and without examination... whose opinions about them were not worth a brass farthing.”

-Autobiography of Mark Twain
User avatar
orion70
VICtalian
Posts: 4337
Joined: Thu Feb 02, 2006 4:45 am
Location: Piacenza, Italy
Occupation: Biologist

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by orion70 »

Yep I guess a bit of alcohol would do. I resuscitated a lot of old carts that way.
User avatar
Mayhem
High Bidder
Posts: 3026
Joined: Mon May 24, 2004 7:03 am
Website: http://www.mayhem64.co.uk
Location: London

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by Mayhem »

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.
Lie with passion and be forever damned...
User avatar
eslapion
ultimate expander
Posts: 5458
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by eslapion »

norm8332 wrote:I see corrosion on the contacts, have you tried cleaning the contacts?
Pure alcohol and a white eraser can do wonders.
Be normal.
lance.ewing
Vic 20 Afficionado
Posts: 413
Joined: Sat Nov 10, 2012 3:19 pm
Website: https://sites.google.com/site/mos6561vic/

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by lance.ewing »

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
Vic 20 Dabbler
Posts: 91
Joined: Sun Nov 26, 2017 6:27 pm
Location: UK

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by siccoyote »

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?
User avatar
Mike
Herr VC
Posts: 4816
Joined: Wed Dec 01, 2004 1:57 pm
Location: Munich, Germany
Occupation: electrical engineer

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by Mike »

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:
User avatar
eslapion
ultimate expander
Posts: 5458
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by eslapion »

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.
Be normal.
User avatar
Mayhem
High Bidder
Posts: 3026
Joined: Mon May 24, 2004 7:03 am
Website: http://www.mayhem64.co.uk
Location: London

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by Mayhem »

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.
Lie with passion and be forever damned...
User avatar
Mike
Herr VC
Posts: 4816
Joined: Wed Dec 01, 2004 1:57 pm
Location: Munich, Germany
Occupation: electrical engineer

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by Mike »

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.
User avatar
MCes
Vic 20 Afficionado
Posts: 457
Joined: Fri Jul 24, 2015 1:19 am
Location: Italy

Re: Vic20 Vixen Switchable 16k RAM Expansion Repair

Post by MCes »

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

http://sleepingelephant.com/ipw-web/bul ... 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....
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." (Albert Einstein)
Post Reply