[fcebreros]

Hi,
I have been playing with my mb-6582 for almost two years without problems and now
the cores began to stop sounding, only core 2 works. UI works fine with non sounding cores.
I have re-uploaded the application and nothing changed.
I have some voltage drops 4.7V and 8.65V but I'm using the same PS as always.
Any ideas?
Thanks

Frank

[Shuriken]

Are you using an old C64 PSU brick?

[Hawkeye]

+1 - just by reading the title, i had exactly Shuriken´s question in mind :-)
While building the mb6582 with lots of power drain on the 5v rail (VFD + backlight LEDs), i experienced some "ultra-slow" startups at voltages below 4.7v, so that may be well the cause.

This post has been edited by Hawkeye: 28 January 2012 - 11:49

[fcebreros]

No,
I'm using a modified modern CPU power supply (switching).
After 3 tries it was the only PS that could deliver enough current.

[Shuriken]

fcebreros, on 28 January 2012 - 15:29, said:

No,
I'm using a modified modern CPU power supply (switching).
After 3 tries it was the only PS that could deliver enough current.

How much current is it rated for?

[nebula]

One good way to tell if your power supply has failed: unplug the LCD. If that doesn't fix things, try also pulling out a PIC and its two SIDs. If the rest of the box starts working, you most likely have a power supply issue. And by "power supply" I mean the combination of your external unit and any regulators you have on-board.

[fcebreros]

Shuriken, on 28 January 2012 - 16:55, said:

How much current is it rated for?

It's rated 18A at 5V, 14A at 12V and I'm regulating down to 9V with a regulator that is rated for 2 A I think.

[technobreath]

Have you ever calculated the current demand on your box?

I have not yet finished building mine yet, and that has a lot to do with the hi demands I put on the powersupply. If you have a lot of leds, and also those for backlight on buttons, it will demand a lot of power.

As for the regulation u mention, the two amp rating is absolute maximum performance in the absolute best environment possible, wich is also in the datasheet. It has mostly to do with heat. It doesn't mean nothing if you have a psu rated 1000 amps if you bottleneck it with a vreg. That vreg will at all times dictate the power delivered.

Though I don't know what type of regulator you use etc. it is important to follow datasheet directions when it comes to heat, input voltage and so on. Reminding you also of the bypass caps u need to use with the vreg.

In general, if you have issues with voltage drops, it is in most cases related to that the load demands more than the supply can deliver. Either because it is underspecd or because of an error in the load. May work some time and stop, or you can get lucky too.

Imho I don't get the thing that seems to be very common - to run delicate equipment like sids and other digital electronics from underspecd or barely just there specd PSUs.

You need headroom on the PSU because of a couple of things. Running it at the limit at all times isn't gonna be stable in the long run, and that things demand more current while starting up.

So my proposal is to do a calculation of worst case scenario current draw, and use a PSU that can handle at least close to it. If current draw is bigger than the PSU can deliver atm, voltage WILL drop, so says Ohm.

Also running it from an old psu with no security measures like a c64 brick... Don't get it, but apparently it works for a lot of us so... Hehe I won't scratch into that too much, but purely for political reasons.

Summary - using a PSU that u have to push to the limit is a bad idea, and if it works, I consider it nothing more than luck! Hehe.

I don't know atm without the datasheet in front what voltage limits there are on the PIC and the SIDs, but check em out and enlighten yourself. Every day I work with searching for errors in electronic systems, and one thing I learned the hard way, is to do it right the first time, and 99% of the hassle is avoided afterwards. And when the strike of unluck is there, there is Always a logical explaination, you just gotta go the extra mile to find it.

First thing is to get the system to operate within limits. If that fails to solve the problem, continue the search for the reason.

U said u tried 3 different PSUs before settling on the one u found to work... It ain't very hard to build yourself a simple PSU that deliver more juice than 2 amps, but of course its confusing if you don't know how, but if u want to learn how, there is tons of experience on the subject shared among some of the guys in this forum...

[Gilesjuk]

Any reason why the MB-6582 (and other builds) is unfused? the c64s have a fuse. I've read that the C64 PSUs tend to fail unsafe and damage the SIDs.

This post has been edited by Gilesjuk: 29 January 2012 - 22:29

[Shuriken]

The biggest drain is on the 5V line. I am pretty sure someone said it's really close to 2A for standard design MB6582. The 9V and 12V are stressed much less.

As Hawkeye said, if you are using high current LCD or VFD and/or bright leds it could be more. I would, like nebula said, decouple lcd and then measure current with your multimeter. If you measure something close to 2A, you can be sure the vreg is just not cutting it.

Gilesjuk, on 29 January 2012 - 22:29, said:

Any reason why the MB-6582 (and other builds) is unfused? the c64s have a fuse. I've read that the C64 PSUs tend to fail unsafe and damage the SIDs.

Yeah if the C64 PSU fails, it usually means you get around 10V on the 5V line. I am also pretty sure that the C64 is not properly protected on the 5v line either. A couple of us have built some protection for this, on the PSU side. There is better ways to do this then just a fuse .

This post has been edited by Shuriken: 29 January 2012 - 23:03

[technobreath]

There is better ways to do this then just a fuse.

Oh yes it is... A fuse will not be working as a single protection. It is simply too slow, and damage will in more than a few cases be the fact.

However, it is of course totally impossible to protect the load 100%. The vreg usually have some protection like thermal shutdown and over current protection and so on. But it doesnt protect itself from short circuits. Here is where the fuse comes to use. Problem is just that the time it takes to blow is more than long enough to cause damage to the synth. Here is where a neat thing called a crowbar comes in handy. Its main component is some kind of parasitic element. It can be a SCR. The circuit is basically a buffer for the fuseblow time... It shorts the supply to ground before damage is done to the load. It keep shorting the PSU to 0volt until the fuse blow and thus turns off the entire PSU.

There are many ways to design a crowbar, some better, quicker and more reliable than others. I would bet the simple circuit variants work good, but the more advanced stuff is faster and more accurate. The main difference between the simple and advanced variants, is the method of sensing the faulty condition and the method of triggering the parasitic element.

Ok, this has all been said before, but i don't remember where, so sorry if this is repeat for some of you hehe.

This post has been edited by technobreath: 30 January 2012 - 00:45

[Shuriken]

technobreath, on 30 January 2012 - 00:42, said:

There is better ways to do this then just a fuse.

[...]

Yes i know Just didn't want to go into the whole crowbar story.

[technobreath]

OMG. That is just embarresing First - that first sentence was meant as a quote of you - it looks as I said it, but...
Second, I just wanted to tell this guy what it is with a fuse alone wich isn't good enough, and didn't remember where the other crowbar fairytale was at, and besides that - I can't help myself telling a good story once I start hehe. - I had some time to kill anyway :P hahaha

This post has been edited by technobreath: 31 January 2012 - 23:34

[Gilesjuk]

It's been couple of decades since I did much electronics and I know the concept of an RCD for mains, so I did hope something similar existed on DC circuits.

I may consider protection on the MB-6582, it's too many SIDs to waste and they're a limited resource.

[technobreath]

Now, I don't know the in depht details about RCDs, but it is a device that is meant for detecting leakage current. The whole concept of the RCD isn't useable at all with DC - as you surely know already . But I think I get why you use that as an example, because protection circuitry in DC and the RCD is alike, but only in the sense that both are in the end current limiters, but the RCD suffers the same issues that a conventional glass fuse suffers under - they break the circuit too slow for sensitive electronics.

What you want (if you need more than the typical 1.5 amp voltage regulator based linear PSU, your best bet would be to use a voltage regulator specd for in example 5 amps. would be mooore than enough for the box of yours. This most likely has an overcurrent protection built in + +. Usually it does everything you might expect of the psu when it comes to protection - exept from protecting the equipment from a short circuit in the vreg itself. Regulation will stop, and voltage will in a otherwise healthy designed psu - rise several volts, and this is in most cases catastrophic if you doesn't have any protection - aka crowbar. As I said, it basically gives the PSU time to blow the fuse before doing any real damage to the load.

Crowbar is essentially a SCR placed in the direction so that when its gate is activated by a sensor - some comparator of some kind, or maybe a zener diode - not a good solution though - it will start conducting. To trigger the scr gate you need a sensor. Can be comparator comparing the voltage on the rail to a referance voltage, and if it goes beyond the limit - bzzzz the fues blows in a secure and controlled way.

So - a fuse without a sensor triggered SCR to really short out the supply, the only limitation for the fuse then is its ratings .