(2022-01-01, 05:29 PM)bodgit Wrote: I use a 1541-U2 with my Beamracer-equipped C64 and I’ve found when entering and leaving the U2 menu that the screen can get corrupted and the machine becomes slightly unstable in general, random crashes/lockups, etc.
On a hunch I took the Beamracer out and now my C64 seems stable again. The Beamracer was inactive at the time so it should be fairly passive. My only thought was my C64 is a long board that has a separate 7805 regulator that provides a dedicated +5V for the VIC and possibly other parts of the machine.
Is the added load of the Beamracer likely to hit the current limit for the 7805? I read somewhere that the normal load is about 250-300mA, how much extra does the (inactive) Beamracer draw? In order to measure it I would have to desolder the regulator in order to put my multimeter in series.
Other than that, does anyone have any other ideas? My C64 has a component mod board and a SIDFX which makes me think I might be hitting a current limit somewhere…
Hi Bodgit,
Depending on what it is currently doing, BeamRacer consumes a little bit less or a little bit more than 80 mA from the +5V pin (VDD - pin 13 - is not used). When deactivated, BR's power use should be below 75 mA. NMOS VIC-II needs around 180 mA of +5V, so the total worst case should be around 260 mA. You can measure it yourself by stacking DIP-40 sockets like in the attached photo (note the removed pin 40).
There are some other components near VIC-II that rely on the +5V CAN supply, but given that the 7805 can easily provide 1A of current, power should not be a problem (and it has not been in our experience so far).
Can you please share more details about your setup:
- C64 mainboard revision,
- BeamRacer revision (see the right edge near top-right corner),
- Version of the C64 power supply,
- VIC-II version,
- Where the component mod board takes its +5V from?
- Do you use BeamRacer's VideoMod Connector or the original adapter?
Also:
- Does instability only occur after entering U2 menu or can it be triggered in other ways?
- Does instability after entering U2 menu occurs every time or from time to time?
- Can you share a photo of screen corruption after using U2 menu?
- Is your SIDFX installed permanently or can be removed for testing?
- Since you mentioned a multimeter - can you please verify that the power supply provides correct voltages?
These are many questions, but hopefully the answers will help us pinpoint the culprit.