[MTE]

Hi

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 6582a)...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...

Regards

[ganchan]

i had same problem with my stereo sid and lcd connected due to bad voltage regulators on the core.

[MTE]

It works now  :D *yayyyyyy

I reheated all solderjoints again, so there was a bad solder I think...

The 5V drops down to 4,86 with all chips mounted....the 9V to 8,8V....looking good, backlight also blending  ;D

But I need bigger heatsinks...man I burned my fingers on the 7809...also the 7805 is glowing  ;D

*WIKIMARKER
Test your C-64-PSU if it will run stable with all SIDs connected ;) .... mine dosnt :(

For Sale  ;D ...

[bugfight]

i would measure current draw on both 9v and 5v regs.
also i read somewhere that cascading the regs in this way can cause oscillations,
maybe the bypass caps are enough to prevent this, but given your experiences here, maybe not.
it may also be more of a problem when the 5v reg supplies more current than the 9v...

[reboot]

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 ...

and what about people waiting for wilba's sids and smash'pcb and never had a commodore ?
maybe the new pcb will have a second rectifier ?

c-64 psu sucks !.....i'm joking...it's always good to recycling as long as it works  ;)

[doc]

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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.

Quote

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!

greets
Doc

[Foona]

Glad it worked out for you MTE :)

Bad solders can be very hard to find,
and even harder on bigger PCB's.

It's gonna be sweet to see the finished project.
Good luck!

[Kartoshka]

Quote

*WIKIMARKER

wow.. i really saw it wikimarkered in neon-yellow, exactly as you said ;D

[MTE]

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  >:(

Now Im still thinking about another solutions...

[Foona]

Aaaaw man  :(
Mabye i jinxed you.

Since i started with th C64 OPT curcuitry iv'e been experimenting with,
different regulators and voltages.

I did too feed 12v into a 5v reg, and true, it gets rather hot.
I had to put a BIG heatsink. It helped but it did not feel stable.
Sounds like there is still some leakage in your system.
I don't want to say this...but...it might still be a bad solder somwhere, or shortage.
And thats even worse, cuz it's a pain to find them even with a strong magnifying glass.


"Dammit captain! I don't,  have,  the power!"

[Jaicen]

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.

[Foona]

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They have a thermal shutdown to prevent damage from shorts

Ah, i didn't know this.

So if they get like really hot..doesen't that mean they are drawing too much current or something?
Or are they just simply faulty/damaged?