Denial

I've recently been rediscovering the various subtle ways of RS-232 connections (like using >=128 for the LFN to get CRLF at the end of a line). One thing I'm still struggling with is checking the transmit queue is empty before closing the channel. The Programmer's Reference Guide says Care should be...

I think the 7417 is gone. The outputs are giving low voltages that don't follow the inputs.

joshuadenmark wrote:Wow thats a cool modification. Does it still run?

Yep sure does, the fit is a bit tight under the keyboard and the ROM creeps a bit at times. I'd like to build a replacement that also pages between the ROM and RAM.

Thought I'd post a picture of the internal memory expansion that I built about 35 years ago. It piggy-backs on the character ROM with a pair of 6116s, the flyleads pick up RAM1, RAM2, RAM3 and VR/W. I also had to mod UA1 to stop the RAM blocks being gated on to the expansion bus, that way the 3K blo...

Well, I've got it out and tried it in a test circuit. It seems to be ok but I've ordered a replacement to make sure. On to UD2 I suppose.

That's UA1, I'm desoldering it now.

A small delay while I completed the RS-232 adaptor is started 30 years ago but the ROMs check out fine. I've also swapped out the 6522s with another pair, same result. That leaves the RAM and other discreet logic that's soldered to the board. Ray's guide suggests UA1 and UD2 as candidates. Any other...

Well an initial check of the top ROM seems to show it contains sensible values. Dumping it is awkward, I'd forgotten how primitive CBM Basic was. Even printing hex requires a page of code, and CRC computation is out of the question as we don't have XOR. I think I might have to dump it to the serial ...

I have a hunch my issue is the ROMs. From memory when I last powered on the drive >10 years ago it failed differently. I think it was the LED sequence that indicated the first ROM was corrupt. I've nearly finished soldering my expansion port breakout board. Once that's done I'll try and dump the con...

Thanks for the tip, I'd better check that before I get the soldering iron out.

I'll probably build a ROM to EPROM adapter, there's ROM images on the 'net.

Not checked the belt yet but it's probably perished (the one in the C2N had). Any suggestions of where to get a replacement?

If the ROMs are the most likely then I think I'll try and test them. I've got the bits to make a prototyping board, this will be my excuse to use them. I've managed to snag a couple of VIAs on eBay. I'll also try and test these, any suggestions on suitable code to do so? Thanks for the offer to test...

Yes, it's a RAM expansion. It has space for ten 2K SRAM and two 2K EPROMs. I don't have the switch on the side of mine, possibly a custom write-protect switch?

I've just dug my VIC-20 out of a long slumber. The computer itself is unscathed but the disk drive is non-functioning. On power on both green and red LEDs come on along with the drive motor. All three then stay on. Looking around on the 'net and found some suggestions for tracking down the fault and...