exxos's Atari, Amiga & retro forum

I am new to this forum, so massive apologies if this topic has been covered before - I searched and couldn't find this exact issue anywhere.

I have an Atari 520 STE with motherboard CA4003290- _ _ _ _ _ REV _ _ _ _ _.

I have installed the Exxos 2023 STE V1 32MHZ BOOSTER PLUG-IN and Exxos 2022 STE TOS SWITCHER.

I did not replace the pull up resistors on the motherboard (which are the original values) because the booster board has "472" stamped on the resistor packs.

The booster is connected to 74F257 and the TOS Switcher using the supplied thin wire.

The 2 large electrolytic caps on the motherboard have been replaced.

I have added a 10K pull up network to the DMA databus. I haven't added the 1772 pull ups as I'm using an original floppy disk drive.

I am using a new Exxos PSU.

The two MC 6850 ACIAs have been replaced with two MC68B50 ACIAs.

I am using a Cool Novelties 13 PIN DIN TO RGB SCART cable.

When using the original 2x Siemens 256k SIMMs (8 x HY B41256-10 chips on each), the image is rock solid and I get no issues when running the GEMBench 6 loop tests for over an hour. The tests indicate that the booster is working correctly as the numbers are very similar to those posted here: https://exxosforum.co.uk/forum/viewtopi ... =24&t=4441

However, if I install more than 512k RAM, the image becomes really unstable with wavy lines and interference. Intermittently, the image will disappear and the screen will go blue. It has this issue whether I use 4x Texas Instruments non parity 256k SIMMs from a 1040 STE, or brand new 2023 Exxos 1MB no parity SIMMs (totalling 2MB or 4MB). Despite the video issues, I can run the loop tests in GEMBench 6 for over an hour without crashes; the only real difference in the results is that ROM Access falls from 309% to 297% with 4MB installed.

Sorry I haven't included a photo - I don't know how to do it on a mobile.

Thanks in advance.

Have you routed the 32Mhz wire similar to below ?

viewtopic.php?p=41199#p41199

I'm afraid it's not an issue I have ever come across or heard about. The amount of RAM doesn't have anything to do with the booster really.

There has been some odd issues with some versions of the STE shifter but its difficult to tell what you are seeing without images/videos.

viewtopic.php?p=73580#p73580

Also have you run YAART to make sure you have not a bad simm socket connection?

I have had this issue before (but I do not remember if I tried different ram amounts, I probably just had 4mb) it's the motherboard in the picture Exxos posted. The screen would go crazy, wavey, weird effect in 33mhz mode. The only way to influence the behaviour was to move the 32mhz clock line away from certain parts of the motherboard. Try routing it like I did (I hot glued the cable to the top edge of chips/sockets to raise it above the motherboard. Then it gets routed around the large shifter chip, around the left side, then to the 74f257.

The board had all the fixes, bus pull-ups, new caps, new PSU etc etc etc. So yeah play with that clock wire. Make sure you're using good quality single core wire.

Thanks, exxos and Steve, for your fast responses.

Here's an image of the problem:


I'll try rerouting the clock wire as I have it running between the SIMM sockets and the shifter. :oops:

Do either of you know a reliable source of good quality single solid core wire if I need it? Ebay is like Russian roulette, but I don't really want to pay hefty delivery charges from Farnell, Mouser etc (and have to buy 100 metres of it) if I can avoid it.

I'll also try running YAART. Some of the SIMM socket connections looked a bit dodgy so I reflowed them all, but it didn't help. I have some new sockets from the Exxos store and will install these if problems show up.

Thanks again.

DementED wrote: 15 Jun 2023 09:32 Do either of you know a reliable source of good quality single core wire if I need it?

To confirm you are using the wire in the kit ? A different wire, your changing the circuit and are effectively performing an experiment.

I very much doubt that the RAM is at fault, but if it works with some RAM and not others it must be connected.

Assuming you have 2x 256KB sticks installed when it works, can you change those 2 sticks for 512K or 1MB, so keeping the same slots, without having the problem?

Can I also ask, have you tried a different display? It may be something relating to your display. I can't say for sure but it would be worth testing.

Exxos - yes, I'm using the wire in the kit. Just wondered whether I can get any spare wire of the same spec in case my wire isn't long enough or snaps (I used some of it to connect the booster to the TOS Switcher).

Rubber_jonnie - I haven't got any 512k sticks, but I confirm that the issue occurred with new 1MB non parity sticks in slots 1 and 3 only. I'll try a different display, but it's weird that the image is 100% stable with only 512k RAM. Although it's only a Matsui TV, it displays NTSC, PAL60 and PAL50 with no issues when hooked up to other machines.

Thanks for all your help.

I'm not totally sure but it is possible the video RAM could be higher up in the RAM when 4MB is used. But I would assume it would fail RAM test if there was issues with RAM above 512K.

Do you have a photo of the mainboard showing the entire board and clock wire run?

A long shot, but are the SIMMS both using the same contact pad metal type?

This used to cause problems with old PCs years ago too, as different metals would create oxidation between themselves.

One type would look a copper colour, the other type is grey/silver.