jaytee

One MB-6582, One Power Supply: a Tutorial

73 posts in this topic

I've got a bit of a dead end here...

And I think it might be due to the C3 cap. My MIDI interface passes the loopback and sysex test. So I've gotten to test #11 of the CORE workup. 

Its stated as follows...

 

 

  • TEST CORE11: The code upload can also fail if no, or a too small bypass cap is connected to the power rails of the PIC. A possible effect is, that for example "F0 F0 F0 F0 7E F0 00 01" will be sent by the PIC instead of the proper SysEx string "F0 00 00 7E 40 ... F7". Another effect could be, that something is received by your MIDI interface, but not displayed by the MIDI monitor because of the invalid MIDI event structure. This all can happen even when the IO and Software loopback test which is discussed below is passing,
    If this happens, check that the 2200 uF cap (C5 of the core module) is soldered properly. If you are unsure about the state of the cap, since you've re-used it from an old device, try another one.
    If you are using the optimized PSU for MIDIbox SID, bypass the outer pins of the (not mounted) 7805, so that C5 has contact with the +5V/Ground rails (see also mbhp_4xsid_c64_psu_optimized.pdf)!

Upon powerup, it doesn't detect the bootloader and sends persistent "F0 F0 F0 F0 7E F0 00 01" messages. 

 

If it is in fact because C3 is too small...Can I just attach the 2200uf in series for testing purposes? 

Has anybody else experienced this issue with the 10uf smoothing cap?

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If you want to try putting the 2200uf cap in while you get MIOS loaded, it should work ok. (Edit: Looking back over the schematics, I dont believe this will solve your issue.) Or at least, it worked fine for me until I installed more than six SID chips; only then did the switching regulator start to choke. OTOH, I haven't had trouble uploading MIOS since changing C3 to the smaller value, so I can't really say what the issue is.

Edited by jaytee

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I followed your issue with the switching regulator. Luckily, I did purchase the 1.5a variant so I'm pretty certain it's not the culprit.

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Even the 1.5A sVreg might choke with an excess capacitance load (it does mention this in the datasheet IIRC). I can't say for sure as I never tested. Even the 1A version worked once I pulled C3 (though I never tested it with LEDs).

Anyway, looking over the Core8 schematics, I'm reasonably sure that C3 is not your issue, as the MB6582 C3 is not equivalent to the Core8 C5 when wired up according to the instructions in this thread. The Core8 C5 (and the MB6582 C3 according to the original power setup) is on the input of the 5V regulator. If you've wired everything according to the instructions here, C1 on the MB6582 takes that role, while C3 is now on the output of your 5V regulator (taking over the role of C4 on the Core8 board).

In other words, if there's a capacitor to blame (and your wiring job is correct), I would look to C1 first rather than C3. Is it in backwards? Soldered correctly? Missing any jumpers? Barring that, what kind of power adapter are you using? How's the wiring where you live? It seems to me that if a too-small decoupling cap on the power rail can disrupt MIOS, then an abnormally noisy or otherwise poor-quality power source could cause the same symptoms (just a guess).

If you can post some close-up, in-focus shots of your board's power section (top and bottom), there might be something there one of us could spot. I would also try a different adapter and a different outlet (in a different building if possible). Let's knock out some of the easy troubleshooting steps before we start mucking with component values (especially since my board and others work fine with these component choices).

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Unfortunately, I don't have a diff 12v adapter I can hack up right now. Will have to buy an older used one and see...Just in case, here's a few pics.

IMG_20170315_133332.jpg

IMG_20170315_133353.jpg

IMG_20170315_133406.jpg

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The only thing jumping out at me from the photos is that you've left C4 (100nF) unpopulated (looks like V1 covers up the pads). C4 is in the original Core schematic (designated there as C3, confusingly enough), it does connect to the possibly problematic 5V rail, and it's the only notable difference between our builds, so it's worth a shot. Maybe you need to surface solder it to the backside to avoid desoldering your sVreg?

Off the top of my head, perhaps the switching Vreg introduces some high frequency noise that mucks with the PIC, and C4 filters that out. It's possible that the troubleshooting document you posted never anticipated the use of switching supplies or regulators, and was therefore focused on the low frequency ripple that the big cap would smooth out.

Also, just to check, you are getting a good 5V supply, correct? If you haven't checked since you started having issues, check that now, just to be sure.

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Also, unrelated to your current issue, but possibly going to save you trouble in the future... As currently wired, you will not have a working 12V rail. I noticed in your earlier picture that all your jumpers were set for 9V operation, so maybe you're already aware, but right now, your 12V regulator doesn't have anything going to its input, and even after jumpering the connection, a 12V wall-wart won't be able to drive the 7812 properly. If you're planning to use only 6582/8580 SIDs, no change is needed.

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Also, this probably isn't the issue, but looking at your solder side photo, there seems to be a few stray flux and solder blobs on the board. None that look like they're your issue, but it can't hurt to clean things up and go over it with a magnifying glass on the off-chance you have a tiny short somewhere.

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Yea, the 12v reg was installed before I decided to ditch the mixed SID config. I am going to be using just 8580's and building a stereo 6581 box later on. I just didn't remove it because it's not hurting anything. 

Yea I checked the board for shorts and will clean the flux up. But as far as the shorts, I found none. No broken traces I can identify either. The traces by B1 are a bit chewed up from when I removed the bridge rectifier but continuity is OK and I covered it up with clear coat.

So I installed c4 on the underside. And still no love...

My 5v rail is good. All points are receiving steady 5v. Pin 2 on the MIDI OUT Jack has 5v.

 

I also went back and jumpered an LED with. 220 ohm resistor in series between pins 26 and 31 of the core module. It lights and flickers during MIDI transmission.

Maybe it's an issue with the optocoupler now I'm thinking. 

One strange revelation, I pulled all the PIC's and tested them in Core 1 to observe. Only 2 of the PIC cause the message flooding in the MIOS terminal.

The other 2 don't return the persistent messages. But the bootloader isn't detected either. Really frustrating. 

I bought these from Mike so they should be burned with the bootloader already...But I don't know how to tell as I don't have a PickIt

Edited by ChinMuzik

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Rats, it would have been handy if C4 were the issue. Definitely still try a different outlet and adapter. And it seems unlikely, but maybe try replacing C1, or perhaps even upping the value slightly (3300uF)? 

TBH, we are rapidly approaching the limits of my knowledge here. If none of the above solve it, it may be best to start a new thread, since it would seem that your power section isn't the issue. Hopefully that will attract the attention of any folks who know PICs and/or Core8 modules better than I do.

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How about the safety of this power supply? How will it respond to over/undervoltage, reversed polarity etc..
I'm considering to mod my MB6582 and those from 2 friends with this, but I want to make sure no SIDs get damaged if a mistake is made.

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It seems to me that at the very least, this setup poses no greater risk than the original power setup, and in many ways reduces the risk. In the old design, the 5V line came directly from your PSU, so if it went haywire, it exposed the MB-6582 internals directly to whatever it was outputting. In this setup, everything past the power section is behind regulators at least.

Wrong polarity will probably blow something in the power section, though I think the regulators protect everything else in that situation. If you wire up your own 7-pin DIN wall-wart like is shown earlier in the thread, it'll be pretty impossible to plug in something of the wrong polarity unless it's a mistake in your wiring; I say just be extra careful.

Overvoltage is tolerated up to a point; check your regulator data sheets to see what kind of voltage input they can tolerate. If input voltage goes beyond that, they'll either shut down or break. I'm not sure what the failure mode of these regulators is (i.e., if they leave an open circuit, short to ground or short to input voltage), but in any case, they'll do the same thing in the old design too.

The only protective measure that this setup removes is the bridge rectifier, which would technically protect against polarity reversal, but is really meant to rectify the 9VAC from the C64 PSU. The original design has no polarity protection for the 5VDC line, for instance, aside from the keyed power connector. If it really worries you, you could probably leave it in—sammichSID has a bridge rectifier alongside a single DC supply, for instance, but that's because it uses a standard barrel connector and could therefore be connected to any number of power supplies. The DIN connector on the MB-6582 prevents that.

IMHO, it's safe enough. Maybe someone else can chime in with additional protective measures you could take.

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Yes, modern switchers are safe enough, if you do it right! :-)
If you have any doubts about modifying already built MB6582s (yes, some things can definitely go wrong there!), better think of either a new external PSU with protection, that is otherwise identical to the C64 PSU (and which has high-quality high frequency switchers to avoid noise) or a protective ciruit after the old C64 PSU, e.g. a crowbar protection circuit with a fuse, that will protect against the critical case of the ancient 5V vreg going haywire.

Reverse polarity protection: best with a high-current diode directly next to the input power socket.
Undervoltage: no problem in the MB6582 context
Overvoltage: should be no problem until a quite high DC voltage (e.g. 36V) is reached for most switchers, the input filter cap will usually blow first and give an audiovisual feedback of something going wrong ;-).

Many greets,
Peter

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Cool thanks for the advice guys.. Ordering parts as we speak..

Any advice on C3 voltage rating? The ones I have here are 16V, considering it's a mixed setup that may be too small?

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When choosing caps, aim for a voltage rating ~2-3 times the expected maximum input.

If you want to protect for reverse polarity, try a 1N5817 Schottky diode. The Vf is low, so it doesn't drop the rail much.

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If you wire things up exactly as shown here, C3 is only connected to the output of the 5V regulator, so a 16V rating is fine.

It does occur to me that C1 (listed as 16V or 25V in the official BOM) should definitely be rated for 25V minimum (maybe even higher), especially if you're running mixed SIDs and therefore need a 15VDC wall wart. I'm pretty sure the one I have installed is still just a 16V, d'oh!

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A while ago I did this mod on one MB6582 and it didn't work. Due to lack of time I didn't troubleshoot it, so now I'm doing the mod on another MB6582, double checking every step.

One thing that confuses me is the pic in the initial post.. It seems to have the Recom part (V4) installed backwards. 111f1FqGis.thumb.jpg.f089256d640f4f270e0

Compare to all other pics in this thread it is installed differently. Looking at the datasheet / pin 1 location, it does seem like the pic is wrong, or its another part/form factor.

 

EDIT: End up building it like I expected worked fine.. Took the older mb, reversed it and bam, works too now.

Edited by rvooh
Update

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The switching Vreg is installed backward from what the original PCB design expects, but it doesn't matter because that Vreg has to be jumpered into the circuit anyway. If you install it exactly according to the instructions in this thread, it'll work (case in point: my MB6582 is the one pictured, and it works).

You could install it the "right" way if you want, but there's no advantage to doing so, and you'll have to adjust your wiring and I think the placement of certain capacitors as well.

edit: I'm not clear on what you mean when you say it's installed differently in this picture than in the other pictures in this thread. The only other pictures in this thread are my own (part is installed the same way in all photos) and ChinMuzik's, who has their sVreg installed the same way (aside from one photo where a *different* sVreg is installed backwards and needed to be fixed).

Edited by jaytee

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look at your picture, bottom right corner: the double line on the silkscreen is visible and the part is overlaying the pcb traces, which suggests the printed side is facing outwards. The legend for pin 1 is correct of course.

in all other pictures, the parts printed side is facing inwards, the double line on the silkscreen is covered and the pcb traces are visible.

 

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As far as I can tell, it's just an illusion. I tried two different Vregs on this project, so it's possible the photo is of a slightly different part, but whatever the reason, I can confirm it was installed correctly and working when the photo was taken.

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I guess it's a slightly different part then :)

 

I started modding the power supply of my mixed SID setup yesterday. I only have 15V, 1A.. Will that be enough? 8 sids, full control surface.
My gut feeling says it's gonna be fine due to the higher voltage.

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Finally got around to doing this, i used have a crackle from time to time in the audio output using an c64 power brick, but this mod seems to have fixed it!

 

huge thanks to altitude for the mod, and to jaytee for the awesome tutorial!

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Do I need to add caps C1, C2, C4, C11 and C12? I'm doing a mixed SID setup. I see everyone has them in the photos in the this thread. The build guide said they were optional and for PSU Options A and B so I might have foolishly not bought them thinking they weren't needed.

Edit:
Never mind, I ended up ordering those pieces just to be safe. If they are required, I'd advocate they be added to the OP

Edited by fallenturtle
Update

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So instead of using the 7809, why not use the 9V version of the Recom R78B5.0-1.5 or something similar since it already has some fancy protection stuff inside? Just because of space issues or is there another reason beside the price?

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16 hours ago, Humpink said:

So instead of using the 7809, why not use the 9V version of the Recom R78B5.0-1.5 or something similar since it already has some fancy protection stuff inside? Just because of space issues or is there another reason beside the price?

Personally, i see three potential arguments for a classic 7809 linear vreg, but they are highly subjective, others may have other thoughts about it!


Here they are:
* it is cheaper :)
* the power draw of the 8580 on the 9V rail is not high, it is "only" used for the analog part of the chips, primarily op-amps, i guess.
* they feed the "analog part" of the SIDs, therefore purists might want to avoid switchers there if possible, even if the recoms have a very high, probably inaudible switching frequency.

Most likely you could install a 9v switching vreg without any problems.
Many greets,
Peter

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