MB-6582 wont' power up when stuffed with 8 sids

Testing/Troubleshooting
1

The baseboard is finished! Without SID chips, the testtone checks perfectly on all channels!

When I stuff 8 SIDs, the thing won’t power up. No LCD, no tone, and a very dim power LED. Remove one SID, and it stays like that for a second or two, then comes on to full power (sometimes…sometimes it’s the same as having 8 SIDs). Remove another SID (6 SIDS total are stuffed) and it works just fine.

All SID chips are fine, I’ve tested each in my CORE + 2 SIDs setup.

It doesn’t matter which SID modules I remove the chips from. Removing the two in SID4 gives the same results as removing two from SID 1, and the same result as removing one chip from SID 2 and one from SID 3.

Straight out of the wall, my C64 PSU plug puts out 5.2VDC and 10.7VAC. All of the voltage checks given in the baseboard construction guide checked out fine.

2

Sounds like it’s simply drawing too much current for the PSU. Do you happen to have another one? Measure the current consumption that might answer that question.

3

I don’t have another, unfortunately.

uh…how do I measure current? the multimeter manual doesn’t really help.

I just tried to do it at J25 and the bridge rectifier almost exploded. The top is a bit melted, but everything still works. I should replace it anyway, right?

4

I don’t have another, unfortunately.

uh…how do I measure current? the multimeter manual doesn’t really help.

I just tried to do it at J25 and the bridge rectifier almost exploded. The top is a bit melted, but everything still works. I should replace it anyway, right?

See this page on using an ammeter. Set the meter to measure DC amps and follow the example in that page. Yes, replace that rectifier. When things get melty it’s a good idea to replace them, even if they seem to work okay.

5

Mine did the same, so i replaced the PS with another.

The one that ‘sagged’ on mine was a beige one, where as the one that worked well was one of those vented black ones.

6

You can’t measure current at J25… that’s just an unregulated output of the rectified 9V AC coming from the C64 PSU.

To measure current you need all the power to go through your ammeter or multimeter. In this situation, you probably have a C64 PSU which is failing to deliver enough current on the 5V supply. In order to test actual delivered current/load, you’d need some way to break the 5V supply “track” and make it go through the ammeter/multimeter before going to the rest of the PCB.

There’s a good place to do this… at J73. Regardless of whether you are using PSU Option A or B, all 5V supply passes through J73. It was a “backdoor” header intended for people to do workarounds etc. so the build guide says:

Solder a bridge at J73 between pin 1 and 2. (This connects 5v from power socket/switch to 5v supply lines).

So remove that bridge… if it’s like mine, and just a U-shaped resistor lead, then cut it and desolder each half separately, soak up all the solder and put in a 2-pin header. Then a shunt/jumper can be used to connect it like it should be, OR you can take out the shunt and connect your ammeter/multimeter there, so all current will pass out of pin 1, through your ammeter/multimeter and then back into pin 2 and the rest of the PCB.

Then you can measure the current, although the load is fairly well estimated anyway and the problem is most likely the PSU unable to deliver 5V at ~1500mA or whatever it really is… I did the math once… but from memory, each SID draws 100mA on the 5V supply, plus you have four PICs and an LCD backlight.

The simplest fix MIGHT BE to move the LCD backlight to the 9V supply (or maybe better, the unregulated supply at J11). I’ve written about this in another thread… I think it was m00dawg or fussylizard’s MB-6582 build… in short, you replace the 5V supply to the J15 B+ pin but NOT to the other pins of J15 or the P1 trimpot. Swapping the supply like that might shave off 250mA of load on the 5V supply, which is enough for two SIDs!

This idea works… I’ve tested it in sammichSID with high-power LCDs that draw >250mA with all current being supplied by the input 12V DC and not the 5V on the PCB. Ideally you should replace P1 with 50K so you have more control over the actual current, and ALSO keep a break in that supply to J15 B+ so you can measure the real current delivered to the LCD backlight and trim P1 to tweak the current, buy you could get away with just replacing P1 with 50K and not going past 50% brightness.

7

Wow…that actually made perfect sense…Electronics lvl up!

Thanks!

8

The one that ‘sagged’ on mine was a beige one, where as the one that worked well was one of those vented black ones.

vented black one FTW… I haz 6.