Question about the 5V RAM conversion

[ApolloBoy]

I'm thinking of doing the 5V RAM conversion to my CV before too long and I've got a couple of questions regarding it. First off, will this completely eliminate the -5V and 12V rails, and second, will getting rid of those power rails have any kind of adverse effects on expansions or AV mods?

[+opcode]

The SGM should work fine with just 5V. Not sure about the EM#1, need to check.

[ApolloBoy]

The SGM should work fine with just 5V. Not sure about the EM#1, need to check.

I've got a Heavy Sixer and 7800 so I'm not worried about losing the Expansion Module 1. I was mainly curious about the SGM, good to hear about that. But now my main concern is whether or not Ben Heck's AV mod will still work.

[ApolloBoy]

One other question, will having only the +5V rail have any effect on the controllers? What I'd really like to do is replace the original power jack with a barrel jack along with a 5V regulator board so that I can use a standardized power supply with the CV.

[ApolloBoy]

Anyone? Real curious as I'd like to start on this project fairly soon.

[wileyc]

Hi there,

 

Although replacing the RAM with straight +5V chips eliminates the need for +12V/-5V from the logic board, the AV circuits need +12V (both stock and A/V mod, assuming that the A/V mod resembles Solarfox's LM318 mod). I learned this the hard way today, after having thoroughly examined the reverse-engineered schematics but not re-examining my A/V mod.

 

The right thing to do, I think, is to wire it for a stock +12V wallwart and feed +5V in via a simple 7805-based regulator circuit. I'm going to do this over the Christmas break; will post the results here.

[+grips03]

Hi there,

 

Although replacing the RAM with straight +5V chips eliminates the need for +12V/-5V from the logic board, the AV circuits need +12V (both stock and A/V mod, assuming that the A/V mod resembles Solarfox's LM318 mod). I learned this the hard way today, after having thoroughly examined the reverse-engineered schematics but not re-examining my A/V mod.

 

The right thing to do, I think, is to wire it for a stock +12V wallwart and feed +5V in via a simple 7805-based regulator circuit. I'm going to do this over the Christmas break; will post the results here.

 

yes, this method makes the most sense.

[wileyc]

Update: I put together a simple 5V regulator circuit using a 7805S (good for one amp, TO-220) and a couple of filter caps.

 

It worked; however, the generated heat caused the circuit to thermal shutdown within a couple of minutes. A decent heat sink would probably fix that; I'll get one the next time I'm in Akihabara. It would probably be better to use a TO-3 can rather than TO-220, but I haven't had much luck finding those lately.

 

It would be nice if the LM318 composite modification could run off just +5V ...

[wileyc]

I ended up wiring a cheap DC-DC converter (Cosel MGFW152405) into the unit. Seems to work okay; the converter runs quite cool. I am now wondering if I can remove the RF daughterboard to reduce the noise in the unit... has anyone tried this?