2 weeks of testing its now time for posting, because I ran out of ideas…
The story…
I finished the basepcb and was testing with 2 different c64-psus…when I connect more than 4 SID-Chips on the board (socket dosnt matter, Ive tested many variations…) the voltages goes down, LCD-backlighting goes dim etc…so Wilba and me was thinking its maybe the type of SID-Chips (I use 6582, not 6582 a )…and so he would send me some a-ones for testing…but before I do this I wanted to test with an another PSU, because I build a FM-Synth also in the same box with the Wilbasid, so I build following last weekend…
This PSU works fine, tested with scope etc…all is perfect, but when I plug the PSU onto the board I got no 5V and the 9V starts at 7V and goes up slowly to 9V in so 5-10 seconds
I have no idea what this can be…as you see on the picture no chips are mounted, so I think it isnt a SIDchip-problem…all is clean, I checked all solders more than 10 times
Maybe anyone have an good idea in which direction I should start to search again…
also i read somewhere that cascading the regs in this way can cause oscillations,
In rare cases, it can. But that doesn’t matter in MTEs case. If the 100n are close to the regulators no problem may occur.
One problem is the current. It makes the 9V regulator very hot. A good heatsink is a must.
You can handle this, if you don’t connect the 5V reg after the 9V. You can connect both Regulator-Inputs together and then take each voltage individual out. Then you have it seperated. In this case the 5V reg will get hot because of the high input voltage (which physical doesn’t hurt the reg, because it can do 30V at the input. But the moreover voltage will be turned into heat).
A good heatsink is a must here, also.
well i had so much problems with 20’s years commodore psu ,i have a lot broken …i made mine
(to my opinion) a commodore psu can be re-use for a simple sid where the cost is part of the projet …
for 8 sids anybody can spend a bit more money …
Thats my opinion also. I’ve opened one C64 to have a look inside. It is a very simple, old circuit. The regulator used is a very old fashioned one (no wonder … its 20 years old).
Most broken psu I saw had contact problems around the fuses or bad solders. This psu is what it is: a 20+ year old brick!
Thnx Foona, but my happiness was too early Im still having problems…the voltage goes down after 5 minutes when the box is connected :‘( :’( the chips suck too many current through the regulators…also I tried to separate the 9V/5V-regs but there the voltage drops more faster down…because I shoot 12V into the 7805, thats too many, bigger heatsinks didnt work too…
Ive tested now some old 486`s PSUs with my scope…but they humm >:(
If the voltage is dropping as the temps go up, it’s most likely the regulators. They have a thermal shutdown to prevent damage from shorts, so perhaps that’s the answer. Also, are you still using the C64 PSU?? I know a lot of the old ones get a bit crazy when they get warm.
*yayyyyyy
… mine dosnt 