MB6582 PSU trouble

MIDIbox SID
1

I’m building an MB SID using the MB6582 baseboard from smash, and I’ve run into a problem. I’m using PSU option B. At J4 I’m measuring just over 5v between 5v and ground, but between 9v and ground I’m only measuring 2.48v and between 12v and ground I get 3.08v. I’ve tried 3 different power supplies, all with similar results. The power supplies themselves are good because I get 5v where I should, and also 9v ac wher I should be seeing that.

If anybody can point me in the driection of what to check, I’d appreciate it.

Thanks,

Jeff

2

First double check all your jumper settings are correct and that you have the correct regulators in the correct places and they are oriented correctly.  If you’re using heat sinks make sure they are not touching since some regulators do not share a common ground.

I’m not sure how you would test power at J4 since that is for configuring how voltages are routed.  I would recommend testing for 9V/12V at say J1_SID1.  Clip ground to the ground pin of J3 (pin nearest you when looking at it from the front) and test for 9V at the left pin of J1_SID1 and for 12V at the right pin of J1_SID1.  You can test for 5V at J3.

3

First double check all your jumper settings are correct and that you have the correct regulators in the correct places and they are oriented correctly.  If you’re using heat sinks make sure they are not touching since some regulators do not share a common ground.

I’m not sure how you would test power at J4 since that is for configuring how voltages are routed.  I would recommend testing for 9V/12V at say J1_SID1.  Clip ground to the ground pin of J3 (pin nearest you when looking at it from the front) and test for 9V at the left pin of J1_SID1 and for 12V at the right pin of J1_SID1.  You can test for 5V at J3.

I’ve got the VRs in the correct places and correctly mounted. The jumpers are also correct. I double checked the VRs and jumpers both last night and agian this morning. But when I measure the voltages at J1_SID1, I get the same meaurements as at J4; ~2.5v and ~3v respectively.

4

Note that the common (middle) pin of V1 (7809, 9V regulator) should be connected to the +5V DC supply… this is how it will output 9+5=14V relative to the ground (i.e. the same ground throughout the PCB which is connected to the C64 PSU ground). So first check you’re actually getting 9V DC coming out of V1 by testing between the output pins of V1, which is the same as testing between the V1 output pin and the +5V DC rail (when using PSU Option B, where +5V DC rail is connnected to V1 common pin).

Then check you are getting 14V DC going into V2 and V3, testing between V2/V3 input pin and middle pin (or ground).

Check the heatsink of V1 doesn’t connect to V2/V3… they share different common pins (i.e. as above, V1 sits on top of the +5V rail).

To correct fussylizard: J4 is just inline with the power supply, it can be used to connect an external PSU (see PSU Option D) or to power other things (if using PSU Option A or B). So testing voltages at J4 is fine, and the same as testing at J1_SIDx

Maybe a short somewhere is causing the voltage regulators to fail. A short causing V1 to not output 9V will cause this kind of problem perhaps.

FWIW I think it’s going to be something simple to find and track down… might take a while though :slight_smile:

5

Note that the common (middle) pin of V1 (7809, 9V regulator) should be connected to the +5V DC supply… this is how it will output 9+5=14V relative to the ground (i.e. the same ground throughout the PCB which is connected to the C64 PSU ground). So first check you’re actually getting 9V DC coming out of V1 by testing between the output pins of V1, which is the same as testing between the V1 output pin and the +5V DC rail (when using PSU Option B, where +5V DC rail is connnected to V1 common pin).

Then check you are getting 14V DC going into V2 and V3, testing between V2/V3 input pin and middle pin (or ground).

Check the heatsink of V1 doesn’t connect to V2/V3… they share different common pins (i.e. as above, V1 sits on top of the +5V rail).

To correct fussylizard: J4 is just inline with the power supply, it can be used to connect an external PSU (see PSU Option D) or to power other things (if using PSU Option A or B). So testing voltages at J4 is fine, and the same as testing at J1_SIDx

Maybe a short somewhere is causing the voltage regulators to fail. A short causing V1 to not output 9V will cause this kind of problem perhaps.

FWIW I think it’s going to be something simple to find and track down… might take a while though :slight_smile:

I appreciate the quick responses, thanks guys! I’ll have to double check again tonight when I get home from work, but I think I had checked the output from V1 and only measured around 3v. Last night, I quickly looked over the solder joints in the PSU section but didn’t see any shorts. I’ll double and triple check again tonight and post the results.

6

To correct fussylizard: J4 is just inline with the power supply, it can be used to connect an external PSU (see PSU Option D) or to power other things (if using PSU Option A or B). So testing voltages at J4 is fine, and the same as testing at J1_SIDx

Ah, right.  I remembered the jumpers on J71 and J72, but forgot that J4 was open.  Sorry for the confusion!

7

It’s worth mentioning that I’ve gone over the solder joints in the PSU section to be sure there are no cold joints and did not see any bridges where there shouldn’t be any.

*editited to get rid of confusing irrelivant information.

8

Please confirm, you’re saying the input pin of V1 is -7.46v relative to the middle pin?

You need to be absolutely specific in what you test, when you report a voltage measurement, specify EXACTLY what you’re measuring between, because in this case, V1 is not connected to ground, and the whole problem is probably related to the voltage regulators not being connected properly.

We’re gonna be here forever if all you report is the input of V1. What’s the output relative to middle pin? What’s the input going into V2 and V3? etc.

Go over my last post and answer all the questions first. I can’t help if you don’t confirm what the problem isn’t.

9

You need to be absolutely specific in what you test, when you report a voltage measurement, specify EXACTLY what you’re measuring between, because in this case, V1 is not connected to ground, and the whole problem is probably related to the voltage regulators not being connected properly.

We’re gonna be here forever if all you report is the input of V1. What’s the output relative to middle pin? What’s the input going into V2 and V3? etc.

Go over my last post and answer all the questions first. I can’t help if you don’t confirm what the problem isn’t.

I apologize for the hand holding here, but I’m afraid that a little bit is neccessary. :stuck_out_tongue:

Please confirm, you’re saying the input pin of V1 is -7.46v relative to the middle pin?

Sorry, I was being dense, I was not measuring between the middle pin and the input pin. When I do so, I get 12.91v.

Then check you are getting 14V DC going into V2 and V3, testing between V2/V3 input pin and middle pin (or ground).

When I measure between the input pin and middle pin on V3, I get 3.72v. The same is true of V2.

10

OK… 12V going into V1 is good.

Now keep in mind, the middle pin of V1 should be connected to the +5V supply.

Now check between the output pin and middle pin of V1. Should be 9V. Note the middle pin SHOULD be connected to 5V but you’re measuring the output of V1 relative to the middle pin, not ground!

Now check between the output pin of V1 and ground. Should be 9V+5V=14V.

This 14V is what should be between the input pin and middle pin (ground) of V2 and V3. You say it is not, well that’s why stuff isn’t working!

Check the bridges J71, J72 and J73. If these are not correct, then things won’t work.

Solder a bridge at J71 between pin 1 and 2. (This connects V1 common pin to 5v, so it outputs 14v relative to ground).

Solder a bridge at J72 between pin 1 and 2. (This connects V1 output pin to 14v supply lines, to go into V2 and V3).

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

What I suspect now is, V2 and V3 aren’t supplied with 14V… maybe J71 isn’t correct. Or there’s a short somewhere near there… you may have mounted the bridges correctly but a short from one of these pins to something else might cause the problems you’re seeing. Check J71 pin 2-3 not shorted. Check J72 pin 2-3 not shorted.

Alternately, some other problem… V1, V2 or V3 are mounted backwards, or V1’s heatsink (which should be at 5V) is touching V2 or V3’s heatsink (which should be ground) or touching something else, making V1 not work.

I know I’m suggesting things you already checked… but it’s the only explanation I can think of.

The next logical step would be, not assume things are correct just because they look like it.

Remove J71 and J72 bridges. Check no two pins of J71 and J72 are connected.

Test V1 relative to middle pin (~12V in, 9V out)

Add bridge at J71 between pin 1 and 2. ((This connects V1 common pin to 5v, so it outputs 14v relative to ground).

Test V1 relative to middle pin (~12V in, 9V out)

Test V1 relative to ground (14V out)

Add bridge at J72 between pin 1 and 2. (This connects V1 output pin to 14v supply lines, to go into V2 and V3).

Test V2 relative to middle pin (14V in, 9V out)

Test V2 relative to ground (14V in, 9V out)

Test V3 relative to middle pin (14V in, 12V out)

Test V3 relative to ground (14V in, 12V out)

11

BTW can you post some top-down photos of the PSU section, maybe some shots of the bottom side as well, around the J71,J72,J73 area.

You know what they say about a second pair of eyes :slight_smile: maybe we could spot something.