MB-6582 base board Problem

[Cassu]

I have a strange problem with my MB-6582 base board (board & kit bought from SmashTV). I bet there is a simple cause for this, but i just cant find it. I have checked everything out several times for the last three days and i just cant find the error.

Here is link to a flash-video what shows you the problem i have. (Contains audio).

http://sites.google.com/site/cassu77/Home/mb_problem.swf?attredirects=0

Any ideas what could be causing this?

Built with PSU option B, and im supposed to use eight 6581 sids.

[nILS]

I honestly can't tell you what's wrong, but without the PICs or the SIDs I wouldn't really expect it to do anything meaningful.

Did you check all the voltages before installing any chips?

Did the LCD show anything (with at least the master PIC installed)?

Did you forget R80?

[Cassu]

I honestly can't tell you what's wrong, but without the PICs or the SIDs I wouldn't really expect it to do anything meaningful.

Did you check all the voltages before installing any chips?

Did the LCD show anything (with at least the master PIC installed)?

Did you forget R80?

R80 is installed.

Problem as i noticed something is wrong:

- All suggested measurements were ok, so i was ready to power it up.

- I turned the power on (Fully constructed with the control surface - except the SID's were not installed yet).

- All audio outs sound like a ship's horn.

- LCD backlight lid up, stayed on about three seconds and then shut off. Some strange characters flashed few times on the display.

- Display got very hot in an instant. I quickly measured the lcd wires and found out that base board's PIN 11 (D2) gave 2,9volts (ground from VSS)!?

- I turned power off and uninstalled all the chips. Then PIN 11 (D2) gave out 4,11volts (ground from VSS) and all audio outs still sound like a ship's horn.

Im puzzled.

I have checked for shorts multiple times, no shorts. I have checked the power trails multiple times - should be ok, since measurements are good to go - except that LCD's D2 pinouts voltage what i think is wrong. I have checked that all the components are as should be multiple times...

Im really starting to feel beaten with this thing...

[nILS]

How about you start from the beginning this time around ;)

Measure all the supply voltages on all IC sockets and the outputs of the vregs again.

If they're not all good - stop right there and find the issue first.

If they're good, install the optocoupler and the core1 PIC only. Connect MIDI in and out cables, fire up MIOS Studio, connect the in and out in the connection window, power up the box and see if you get an upload request (make sure MIDI IO is jumpered correctly on the pcb).

Dropping by the chat might be a good idea as well, as the mb6582-Master Wilba tends to hang out there ;)

[Wilba]

This sounds like a voltage regulator problem perhaps... or the C64 PSU is faulty.

You say you are using PSU Option B... did you check the bridges are correct for J71, J72 and J73?

Please explain what "PIN 11 (D2)" means.

Try one thing now (to help diagnose the problem):

Take out all the jumpers in J1_SID1, J2_SID1, J1_SID2, J2_SID2, etc. the ones that select which voltage that SID will use (9V or 12V). With these taken out, the SID module should not have a 9V/12V supply so if there is still hum on the audio outputs, that's VERY strange, if there is no hum, then we've isolated it to a problem with the voltage outputs (or at least can check them next).

What can happen is, if the 5V supply of the C64 PSU is faulty, then for PSU Option B, so will the 9V/12V supply, because the inputs for V2 and V3 are the SUM of the 9V regulator V1 and the regulated 5V supply from the C64 PSU.

[Cassu]

This sounds like a voltage regulator problem perhaps... or the C64 PSU is faulty.

You say you are using PSU Option B... did you check the bridges are correct for J71, J72 and J73?

I've Checked those bridges many times. I first tried my best to solve the problem by myself.

Please explain what "PIN 11 (D2)" means.

J15_CORE1 (where the LCD-cable goes), PIN 11

Try one thing now (to help diagnose the problem):

Take out all the jumpers in J1_SID1, J2_SID1, J1_SID2, J2_SID2, etc. the ones that select which voltage that SID will use (9V or 12V). With these taken out, the SID module should not have a 9V/12V supply so if there is still hum on the audio outputs, that's VERY strange, if there is no hum, then we've isolated it to a problem with the voltage outputs (or at least can check them next).

I removed the J1_SID1, J2_SID1, J1_SID2, J2_SID2, etc jumpers. Hum is gone! :)

So i'll check out voltage outputs ...

What can happen is, if the 5V supply of the C64 PSU is faulty, then for PSU Option B, so will the 9V/12V supply, because the inputs for V2 and V3 are the SUM of the 9V regulator V1 and the regulated 5V supply from the C64 PSU.

Voltages i have measured from those regs seems to be ok, i'll measure yet again. I have tried two C64 PSU's, result is the same - and both PSU's works fine with my C64's. (No, not the C64C-model, i dont like it. I mean the good old breadboxes).

...but i'll do some more checking...

[Wilba]

J15_CORE1 (where the LCD-cable goes), PIN 11

OK... when you said "PIN 11" you also said "(D2)"... and I was counting pins from the MB-6582 PCB labels, which increment left side then right.

However, your pin counting is common, as it also matches order of wires in a ribbon cable/IDC connector.

So look at the Core schematic just one more time to confirm that you refer to pin "D2". Note that MB-6582 PCB J15_CORE1 matches J15 in this schematic (i.e. it is in the same position next to the PIC) but some pins should not be connected!

Look closely at the PCB drawing at J15_CORE1:

http://www.mb6582.org/plans/MB-6582_Base_PCB_R2_Color.pdf

The tracks leading away from D0, D1, D2, D3 (according to same pin numbering, pins 9,11,13,15) go through a "solderable jumper" on the bottom of the PCB (it looks like two rectangles with a small gap between them). These are in case your LCD does not work with 4-bit mode and you need to use 8-bit mode. So normally you do not solder them or short them with wire etc. you just leave them alone.

For you to get any voltage on D2 (with no LCD connected) is a fault - because it should not be connected to anything on the PCB. The same applies for all four pins D0, D1, D2, D3.

I will let you check this and help you more afterwards.

[Cassu]

OK... when you said "PIN 11" you also said "(D2)"... and I was counting pins from the MB-6582 PCB labels, which increment left side then right.

However, your pin counting is common, as it also matches order of wires in a ribbon cable/IDC connector.

So look at the Core schematic just one more time to confirm that you refer to pin "D2". Note that MB-6582 PCB J15_CORE1 matches J15 in this schematic (i.e. it is in the same position next to the PIC) but some pins should not be connected!

Look closely at the PCB drawing at J15_CORE1:

http://www.mb6582.org/plans/MB-6582_Base_PCB_R2_Color.pdf

The tracks leading away from D0, D1, D2, D3 (according to same pin numbering, pins 9,11,13,15) go through a "solderable jumper" on the bottom of the PCB (it looks like two rectangles with a small gap between them). These are in case your LCD does not work with 4-bit mode and you need to use 8-bit mode. So normally you do not solder them or short them with wire etc. you just leave them alone.

For you to get any voltage on D2 (with no LCD connected) is a fault - because it should not be connected to anything on the PCB. The same applies for all four pins D0, D1, D2, D3.

I will let you check this and help you more afterwards.

"solderable jumper"s are all open, i did not touch / solder those (i've been reading  the construction manuals very very carefully).

There is no voltage in the D2, its cold as i have measured it now few times again - so forget that.

One of the LCD-modules chips is getting hot as hell. It seems that my LCD-module is faulty. I'll buy a new one... Backlight wont keep on and it shows some bizarre lines, effects and characters.

I measured all once again, inserted the chips, plugged it to MIDI and ran MIOS studio. Seems to work fine there, upload works like a dream.

Now i'll wait until i get a new LCD-module. Takes a week or two.

Now im going for a vacation for few days...

Maybe it works like it should afterall, i just might be panicin for nonsense :)

[Cassu]

Now its confirmed; that LCD-module i bought from Mouser is broken, everything else works.

Testplay via midi is done.

Receives midi as it should, SID's squeak out notes as should.

Its just a bit hard to use that thing without a display ;)

Well, takes week or two until i get the new LCD-module.

Background hum (generated by the C= PSU, i think) is quite nasty.

Its irritating and something i really need to get rid of or i cant use this thing to music production as much as i was planning to  :-[

[Futureman]

Background hum (generated by the C= PSU, i think) is quite nasty.

Its irritating and something i really need to get rid of or i cant use this thing to music production as much as i was planning to  :-[

Did you ground the audio inputs? (Use jumpers to connect them to groud) This will cut down background noise by about 80%

Regards

Mike

[Wilba]

Background hum could also come from a C64 PSU that's not working well... try a different one if possible.

[Cassu]

I did ground the audio inputs, no change on the hum level.

I have tested three PSU's, no change on the hum level.

Its pretty loud ... http://cassu.net/mb/mb_hum.mp3 [783K]

Edit:

- Recorded from the first pair of 6581 SIDs.

- Hum volume is even in all four pairs.

[fussylizard]

Do you only get the hum after you play a note, or is it always there?  The 6581 I initially tried never seemed to get the release volume all the way to zero.  I'm now using 6582s and they are much lower noise.  If you can test w/ different rev of SID that might be interesting (easier said then done of course).

Took a quick peek at the signal and it appears to be peaking at around 100 hz, not the usual 50 or 60 hz ground loop hum.  The waveform sort of reminds me of the TB-30, so if you can figure out how to change the pitch maybe it will be a highly-sought-after modification.  Don't forget to run it through a distortion pedal! :-)

hum.PNG

hum2.PNG

hum.PNG

hum2.PNG

[Wilba]

OK... three PSUs, no change in hum level, I would now start considering something wrong with the voltage regulation.

fussylizard says the hum is around 100Hz... if you're connected to 50Hz AC mains power, then the input into the bridge rectifier looks like 50Hz sine wave:

then after the bridge rectifier, you'd get a waveform with peaks at double the frequency:

so if your smoothing capacitor after the bridge rectifier isn't working properly, you won't be getting smooth input into the voltage regulator like so:

it will be more "lumpy", which will translate into a hum in the audio output. Perhaps. I'm not an expert in these things.

So maybe the capacitor C1 is the problem.

You could first check the joins, and try resoldering the joints to see if that helps.

Then if it doesn't help, you could take it out and put the C2 capacitor there. It's OK to have C2 empty, because it's purpose is to reduce possible digital noise on the 5V supply... there is already a regulated 5V supply coming from the C64 PSU brick, and C4 is there also.

I don't really know how you could test the C1 capacitor, I can only suggests replacing it. Perhaps if you tried temporarily soldering another big capacitor in parallel (i.e. onto C1's pads under the board), this might be a quicker way of testing if the problem is no smoothing before the regulator.

If that does not help, you could then perhaps blame the 7809 in V1, or the 7812 in V2... unlikely but possible.

Finally, voltage regulators can fail under heavy load... and since the 12V is generated using the 5V supply, that means if the 5V supply is not stable because of too much load, then the 14V going into V2 won't be smooth.

(p.s. pictures borrowed from http://www.kpsec.freeuk.com/powersup.htm )