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MB-6582 current draw


jaytee
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So I just finished my MB-6582 base PCB. I tried it out with the first two SID chips mounted, success! Beautiful. I mount the other six SIDs....nothing. No startup tones, no LCD activity (not even a backlight). Uh oh. I removed half the SIDs (cores 2 and 3 FWIW) and everything seems to work again.

Am I correct in thinking this is an issue of current draw? I am using a regulated 12V 1A supply (using Altitude's single supply approach), which I figured for sure would be enough juice (in the thread for the single supply, Altitude mentions only drawing 800mA with eight 6582s and a fan, and I don't even have a fan). Perhaps not? Is there anything else it might be?

edit: And if it is just a matter of amperage (looking through old threads, I do see a few people referencing their MB-6582 drawing 1A or slightly more) can anyone suggest a decent power supply? I hate looking for this stuff; I don't want to run my precious gear off the cheapy-cheap switching supplies that are everywhere.

Edited by jaytee
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Me also thinks, it might be a power problem, if you have a display with a bit higher backlight current draw, you will be over 1A/12V... you might want a bit beefier PSU (it is never good to be so close to the limits). To test this, you could measure the 5V line with two and all eight SIDs installed. If the voltage drops then below a certain value (say something like 4.7/4.65V, but is clearly above 0V, which would indicate a short), that is a sign of a power supply overload issue.

But as Zam said, it could also be a short somewhere (if your readout above shows something close to 0v). Not necessarily a defective SID, but maybe also a problem on the baseboard, that will only be visible, when a SID is installed. To test this case, install the two working SIDS into all engines (2/3/4) and try to power-on. To test for defective SIDs instead, try the non-tested SIDs in the otherwise working first engine SID sockets.

Best regards and have a great weekend!
Peter

 

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Alright, I did some testing.

First off, I gave the solder side of my board a thorough once over. Cleaned up questionable joints, got rid of flux splatter and errant blobs of solder, just generally cleaned it all up.

I powered it up with four SIDs again—numbers 1,2,7&8—just to be sure that still worked. All good. I measure current draw, it's around 350mA.

I stuff one additional SID in slot 3. It works. Try it in slots 4,5&6. It works. Leave it in slot 6.

I stuff a sixth SID in slot 3. Everything still works.

I stuff a seventh SID in slot 4. Nothing. Try it in slot 5. Nothing. Remove that SID and try the eighth SID in slots 4 and 5. Nothing.

I remove the working SID from slot 3 and stuff the eighth SID there instead (so again, back down to six SIDs). It works.

So it seems that it's only related to how many SIDs are stuffed, not where they get stuffed or which SIDs I use.

 

Now I'm thinking it really is a matter of current draw. I test the current draw with six SIDs installed (working). About 550mA. I install a seventh SID. Current draw drops to about 360mA and as expected, the MB-6582 doesn't boot.

 

Is my power supply crapping out? This is the one I use. I've been using it with my sammichSID for years.

 

Any ideas?

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Hello jaytee

 

Is there a local regulator at the MB6582 for the 5V rail ? because the supply you show is 12V :confused:

In this case we also have to know the amperage at 12V supply output, not only the 5V rail...

For the 5v rail, If I do little math, 4 SID installed is about 90mA per SID, considering all other component and the 70mA/SID (datasheet I just read) I gess it make sense (I don't know this build)

Now adding two SID increase to 550mA, which is 200mA more, 100mA per SID, for two SID alone (all other component idle already in the previous measurement)

So your already have a problem at this point, not enough to shut down the unit, but supply start failing...

 

Try another PSU, (and use an autotransformer if you can for this kind of trouble shoot)

Best

Zam

 

 

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Zam: I think he is using Altitude's proven 5V switcher approach, that should be fine, and i agree with both of you, maybe the PSU just does not deliver the promised amount of current. I also think, that SID chips may have certain variations in power consumption.

Six SIDs and 550ma sounds well within acceptable range for me, that voltage and current drops after installing the seventh SID (oh yeah, a new songtitle :-)) indicates an overload condition either on the 5V switcher or on the initial 12v power supply (and i really think it is the latter!)

Suggestion: Replace it for a 12V/2A PSU and check again...

Many greets and good luck!
Peter

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No problem with a SMPS, but is it really necessary? It might introduce noise, if the switcher is bad (if you have the specs and have a high switching frequency guaranteed, don't worry about that point!).

A simple transformer -> diode rectifier -> smoothing cap array will do the job fine (aka an unregulated power supply), you have two regulators bringing it down afterwards: a 5V high-quality switcher for the digital parts and a 9V linear vreg for the SID opamps (analog part), no need to have an exact, regulated/switched 12V input...

Many greets,
Peter

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Ok. So I had a cheap wall-wart Amazon Prime'd to my house. Didn't want to spend a lot of money on the off-chance this wasn't my problem....and I'm glad I didn't. Hooked up to a 12V 2A supply, I have the same issue. Up to six SIDS, everything is gravy; once I put a seventh and/or eighth in (no matter which SIDs or which slot) then MIOS fails to boot, LCD backlight doesn't turn on and basically nothing happens.

Is my 5V regulator the next thing to check? Is there any way to check it without just ordering a new one?

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Oh! Good you did not order an expensive 12V PSU and sorry for the wrong advice! It seems Zam was right all the time!

Did you measure the current previously on the 12V line or on the 5V line? Might it be, that the Recom has to provide > 1A after installing the 7th SID (that should not be the case...)...
In other words, are you using a fan or a display,  anything that might be power hungry on the 5V line?
For testing, could you disconnect the display, install a 7th SID and start it up? Do you get the startup sound?

Best regards,
Peter

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Hmm, my one is 1.5A, but if others are using it okay it's a puzzle. It would be good to connect the 5V post-regulator through a multimeter to be sure on the current. You may have a sVreg that's going into overcurrent shutdown too early. Some things clamp at half the rail voltage -- could explain your 2.45V.

Another possibility is  an inrush current problem. Can you try to sequence the startup with the LCD initially disconnected?

Is everything else standard with your build? No ultra bright LEDs or anything fancy?

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@Hawkeye, @latigid on, great minds think alike, eh?

Earlier when I was measuring current draw, it was on the 12V line coming directly from the power adapter.

With seven SIDs installed and no LCD connected, there is still no startup tone. (This is actually one of the first things I checked last week, but I checked again just now to be sure.) Right now, there is no CS attached, so no weird LEDs or anything else that might be drawing extra current.

I suppose the next step is trying to carefully desolder the Vreg and resoldering it with one leg out to measure current? I'll do that now.

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Hah, duh. Wish I had checked this thread again before firing up the iron.

 

Anyway, pulled the R785.0-1.0 and breadboarded it for easier debugging. Double-checked that it's hooked up correctly by running it in this configuration: same results as before.

With my multimeter in series with the 5V line, I measure:

6 SIDs: 710-730mA

7 SIDs: 730-760mA

8 SIDs: 810-840mA

I also want to note that I get slightly different behavior when my meter is in series like this.

- No matter how many SIDs are stuffed (6, 7, or 8), the LCD acts kinda funny—like the contrast is worse or uneven, maybe the backlight is dimmer and it is not nearly as responsive.

- It seems to boot with a 7th SID installed, but still not that 8th one.

- A couple times, it seemed to struggle to boot with just six SIDs installed. It would hang on "Launching CS..." or reboot itself. Perhaps this one is down to iffy connections. Between the breadboard and the alligator clips/probes, it wouldn't surprise me if something just lost connection briefly, especially since this happened just a couple of times while testing and retesting and testing a third time to be sure, but figured I should mention it for the same of completion.

 

So anyway, still kinda stumped. 

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2 hours ago, latigid on said:

Also:

If you have the large caps in there, removing them or adding the flyback/Schottky diode could help.

 

 

@latigid on, just saw this, must have missed it while writing my own response. I saw this in the datasheet and thought it might be related, but didn't really understand what it meant.

 

Are you talking about the 2200uF caps? For the flyback diode, is 1N4148 ok? I don't think I have anything else handy. Edit: I do have a 1N4001 power diode here too.

Edited by jaytee
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Thanks for measuring! 840ma of 1000ma is too close, as there isn`t even the CS installed... subtract 10% error and it will go into shutdown...

Upgrade the switcher to 1.5 amps... that is also the spec of the 5v rail of the original C64 PSU...

Many greets, Peter

 

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