Sammich SID Voltage Issue / Ground Fault

[Pete Brown]

I just completed my build of my sammichSID kit. I've had the kit for a while, but just now got some time to wrap it up :)

I'm doing the voltage tests, and just not getting what I had expected. My power supply is tip positive 9v, as recommended in the build email. I'm using 6582a SIDs.

I haven't connected the control board yet, just testing the base board. I do not have any jumpers installed so it is as-shown in the build guide testing pic.

• On the power supply, I measure 9.06v
  
• On the +5v locations on the base board, including the leg of the VR, I only measure 4.05v
  
• On the +9v locations on the base board, I measure 6.43v
  
• On the +12v location on the base board, I measure 7.78v
  

I did a continuity test in several places and the +12v (or 9v in this case) and ground test points are shorted. +5v and ground are not shorted. I assume that isn't normal :) I'm at a loss as to where the ground fault could be. There's no continuity with the heat sink, so that's not the cause. I don't see any obvious solder bridges. I suspect the fault is inside something, but I have no idea where to begin looking (I'm new to this). If the VRs were toast, I assume they'd just let full voltage through.

Any ideas?

Pete

[nebula]

I don't know about the "build email" you're referring to, but sammichSID Build Guide 1.0 (the latest) is available at http://www.midibox.org/dokuwiki/doku.php?id=sammichSID#sammichSID_build_guide

You need a regulated 12V external power supply for sammichSID. Maybe you read the paragraph on page 17 of the build guide that says the 6582 SIDs require 9V? This is true about the SIDs themselves, but not the external power supply. Read page 17 from the top.

Plug in a nice 12VDC supply, place the jumpers correctly and you should see 9V on the SID sockets.

To answer your last question, malfunctioning regulators can be rather unpredictable. Sometimes they allow overvoltage, sometimes the voltage comes out low, sometimes they open, sometimes they oscillate. As an aside: I read your post several times, confused, because "VR" to me means "Variable Resistor". I recommend you just use the term "regulator".

Good luck, and welcome to the forum!

[Pete Brown]

I don't know about the "build email" you're referring to, but sammichSID Build Guide 1.0 (the latest) is available at http://www.midibox.org/dokuwiki/doku.php?id=sammichSID#sammichSID_build_guide

It was some email Jason and I exchanged when I first got the kit. Since I was using 6582a, I didn't need 12v. Maybe I misunderstood. No worries, as I can dig up a 12v supply if needed. I've been using the 1.0 build guide.

You need a regulated 12V external power supply for sammichSID. Maybe you read the paragraph on page 17 of the build guide that says the 6582 SIDs require 9V? This is true about the SIDs themselves, but not the external power supply. Read page 17 from the top.

Plug in a nice 12VDC supply, place the jumpers correctly and you should see 9V on the SID sockets.

To answer your last question, malfunctioning regulators can be rather unpredictable. Sometimes they allow overvoltage, sometimes the voltage comes out low, sometimes they open, sometimes they oscillate. As an aside: I read your post several times, confused, because "VR" to me means "Variable Resistor". I recommend you just use the term "regulator".

Thanks. Nevertheless, I have continuity between ground and the 12v lines. I assume that isn't correct.

I did the painful removal of the 7809 9v regulator and I still have continuity between the input (12v in the guide) and ground, so it wasn't the regulator. Bummer, I was hoping that was it. It's only on the 12v (input voltage) side of things, though, not on the regulated 9v line or 5v lines on the board.

Good luck, and welcome to the forum!

Thanks. :)

Pete

[Pete Brown]

Replaced the 7809, made up a plug and attached the whole thing to 12v power supply and I get the correct voltages at the couple points I tested. However, I still see continuity between ground and input voltage.

I have to hop on a plane so I can't debug any more this week, but unless someone tells me this is normal, I'm not plugging any chips in :)

Pete

[nebula]

If you're seeing voltage while the board is powered, but then you remove the power and you get continuity at the same point, then your continuity-testing instrument must be getting tricked by a load.

Try measuring resistance (in ohms) instead of simply measuring continuity. A short should appear as < 1 ohm.

Also, make sure your transformer is not plugged in to the board (even if it is unplugged from the wall) when you are making these measurements.

If you're still seeing a short, maybe check the orientation of the bridge rectifier?

Edited October 18, 2011 by nebula

[Pete Brown]

If you're seeing voltage while the board is powered, but then you remove the power and you get continuity at the same point, then your continuity-testing instrument must be getting tricked by a load.

Try measuring resistance (in ohms) instead of simply measuring continuity. A short should appear as < 1 ohm.

Thanks. The meter (BK Precision) is a good one with a dedicated continuity test mode. I tested for continuity with the power unplugged from the board. Interestingly enough, I only get continuity if I have the polarity set a certain way (red probe on ground vs. +12v, although I forget which one it is). I assume that's due to a diode or something, but I'm really new at troubleshooting stuff like that. I'm much better at code :) I don't get a similar result on any of the other voltage traces on the board, just hte 12v stuff, both over at the LCD power jumper and the regulator and jumpers the power input section.

Also, make sure your transformer is not plugged in to the board (even if it is unplugged from the wall) when you are making these measurements.

If you're still seeing a short, maybe check the orientation of the bridge rectifier?

I'll double-check that when I get home. It was lined up with the outline on the board and matched the photos, however. I'm really at a loss as to what it could be.

I assume no one else with sammichSID boards has continuity between +12v and ground, and that this is a soldering error on my part. of course, I don't think I checked before I started soldering, so I can't guarantee it isn't a defective board. O_o.

Pete

Edited October 20, 2011 by Pete Brown

[nebula]

If you're only seeing continuity with the polarity one way, you're likely just seeing the bridge rectifier. I suspect there's nothing wrong.

I admit I still haven't finished my sammichSID, but of all the projects I've ever built - MIDIbox and otherwise - I don't recall ever checking continuity between gnd and +V after the components are loaded.

If you're seeing voltage when the power supply is connected, and no smoke, there can't very well be a short!

Have a nice trip...

Edited October 20, 2011 by nebula

[Pete Brown]

Thanks for your help, @nebula.

Since I get the correct voltage at all the right points when I use a 12v power supply, and no blue smoke, I'm going to assume it's just my testing approach like you described. I'll check one last time before putting chips in, of course.

I should have a proper 12v power supply waiting for me at home (I was using my bench supply with a cobbled up connector for testing 12v). I can't stand wall-wart types as they use up too much space on the power strip, so I ordered one with a separate cord. Now I'm looking forward to getting back and making some noise :)

Pete

[Pete Brown]

You were right, it must have been the diodes throwing off my testing. Voltages all checked out and, after some hiccups with the opto-isolator, everything is now up and running.