SammichSid voltage control failure

MIDIbox SID
1

http://discourse.midibox.org/t/topic/14942

I’m using this power supply (which I remembered was regulated, but now I’m not so shure…) setted to 12V pin-positive.

I checked the control board too and there is everything ok except for the lcd: if the two boards are stacked toghether and feeded with current, the lcd is supposed to lit even if there’s no chips inserted, am I right? I mean, the lcd should show “black squares” in the the upper row (I suppose).In my case it is totally off.

Thank you for your support. I’m new in the forum and in electronics so please be patient with my mistakes and low preparation.

2

If it has a polarity switch i think it’s safe to say its regulated.

3

If it has a polarity switch i think it’s safe to say its regulated.

Absolutely not. Most DC power supplies (especially the multi-voltage ones) have reversible tips, regardless of whether they are regulated or not.

The best way of checking if it is regulated is by using a multi-meter. The “no load” voltage should be exactly the voltage you expect (i.e. 12V) and not something way higher (like 15V).

In this case, the voltage is higher than 12V because it’s unregulated. Take out the shunts in JBP, this is ONLY required in the special case of using a regulated 12V DC power supply to power 6581 SIDs.

Set the brightness pot to fully anti-clockwise.

Assuming you are using the high-power LCD I sell…

Check the shunt in JR4 is in.

Check the shunt in JBL is in “12V”

Remove all ICs, connect the boards, power it up. If you don’t get any backlight or “squares” on the LCD, then you’ll need to check solder joints on the headers connecting the LCD to the base PCB.

If you want to test the backlight circuit, you can do this by setting JR4/JBL to “low-power” backlight settings (no JR4, JBL=“5V”) and inserting an LED into the top two pins of J16 header (cathode in pin 16, anode in pin 15).

4

Silly me, i thought that unregulated implied an AC adapter.

5

Ok, I bought a new power supply which is regulated 600 mA 12V tip-positive. I checked the “no load” at 12V on the power supply and it gives me exactly 12V so, as Wilba suggested, it is supposed to be regulated.

I set the JBL shunt on 12V position, then I put a shunt on JR4, no shunts on JPB and the JP shunt in 6581 position. I checked the voltage in orange points and it gave me 10,5V.

Once connected the two boards the LCD came to life as I saw backlight and the “squares” displayed on its upper row, but after 5 minutes the backlight started to blink and in the end it went totally off; I can still see the squares row, so the LCD is working.

As far as I can check I cannot understand where the problem is. Is the LCD backlight definitely dead?

As I have two 6581 and a 12V regulated power supply I have to set both the two shunts in JPB, right?

6

Ok, I bought a new power supply which is regulated 600 mA 12V tip-positive. I checked the “no load” at 12V on the power supply and it gives me exactly 12V so, as Wilba suggested, it is supposed to be regulated.

I set the JBL shunt on 12V position, then I put a shunt on JR4, no shunts on JPB and the JP shunt in 6581 position. I checked the voltage in orange points and it gave me 10,5V.

Once connected the two boards the LCD came to life as I saw backlight and the “squares” displayed on its upper row, but after 5 minutes the backlight started to blink and in the end it went totally off; I can still see the squares row, so the LCD is working.

As far as I can check I cannot understand where the problem is. Is the LCD backlight definitely dead?

Possibly, but equally possible is a bad solder joint in the brightness pot, the BC337, or a dead BC337.

Note I’ve run my LCD backlight with a similar setup and not killed it, but I don’t set the brightness pot past halfway. Was the brightness pot set to minimum (fully anti-clockwise)? or did you have it at maximum? It might be relevant to what could have gone wrong.

It also could be too much current load, but that seems unlikely with 600mA rating and no SIDs installed.

What kind of power supply is it? If it’s switchmode, they can sometimes do crazy things that I can’t explain.

I recommend testing the backlight pins on the base PCB with a LED. As above:

If you want to test the backlight circuit, you can do this by setting JR4/JBL to “low-power” backlight settings (no JR4, JBL=“5V”) and inserting an LED into the top two pins of J16 header (cathode in pin 16 “B-”, anode in pin 15 “B+”).

Test the voltages of the B+ and B- pins relative to ground and report them here… it will help work out what is wrong.

Try turning the brightness pot, check that the backlight circuit is actually limiting current. If the LED lights and you can change its brightness, the problem is probably with the LCD backlight. If the LED doesn’t light at all, then the LCD backlight is probably OK and there’s something wrong with the current limiting circuit (the BC337), though the LCD backlight could also be dead too. I recently fixed a problem where the LCD backlight, the LCD logic AND the BC337 were dead. Don’t ask me how that happened, but it can.

Do a few tests and get back to me via email… it might be quicker to just assume the LCD is dead and I send you a new one… but you could try to replace the BC337 first.

As I have two 6581 and a 12V regulated power supply I have to set both the two shunts in JPB, right?

JBP, not JPB, but yes. Those shunts are essential to getting the “orange points” (also the SID voltage) exactly 12V. But this is unrelated to your LCD issue… putting shunts in JBP will only increase the voltage to the backlight to 12V, the problem isn’t lack of voltage there (it did work without JBP shunts, it should again).

7

Was the brightness pot set to minimum (fully anti-clockwise)? or did you have it at maximum? It might be relevant to what could have gone wrong.

I started with the pot all the way counterclockwise (as you told me) then, once the backlight was on, I turned it half-way clockwise to have a good backlight intensity.

As soon as I can I’ll perform the test on backlight pins. Thanx for your fast answers.

8

I performed the backlight test annd this is what I got:

  • the led lights up

  • the led light is absolutely not affected by backlight trimpot settings

  • the voltages are +5V at B+ and +3,13V at B-

9

I performed the backlight test annd this is what I got:

  • the led lights up

  • the led light is absolutely not affected by backlight trimpot settings

  • the voltages are +5V at B+ and +3,13V at B-

  • if I connect the two boards the backlight is still off

  • the voltages measured on the top of control board are +5V at B+ and +1,16V at B-

When I do the same test with a green LED, I get voltage at B- of 2.77V with trimpot fully anticlockwise and 2.60V with trimpot fully clockwise. The difference in brightness is very small. Maybe you’re using a red LED for testing, and the voltage drop is 1.8V so these results are “normal” for a working backlight circuit. Or something else could be wrong, I’m not sure.

Last time I did this test, the LED didn’t work, and I wasn’t getting those kind of voltages and replacing the BC337 fixed it. But I don’t think you need to because you are getting some current sinking from the BC337. So now I think that it’s most likely the LCD backlight is faulty and not your PCB… so the easiest way to prove this is just send you a new LCD and header.

10

Ok, after a looooong time since my last comment, here I am writing again on my LCD.

Wilba, thanx for the replacing parts, but it was not an LCD backlight failure as I’ve substitued it with the new one you sent me and, as the previous, it has no backlight too.

So the problem is elsewhere. And my knowledge in electronics isn’t too good to understand where. As the lcd is working anyway and I’ll use the Sammich only in studio I’m going to leave it as it is.

Now I’m experiencing problems with the midi as I’m not able to load the firmware. By the way I’m reading the forum and I know it is a common issue… I’ll perform some tests before posting here.

Thank you for your help

11

Regarding backlight, perhaps replacing the BC337 will fix this, and checking the joints for the brightness potentiometer.

Regarding MIDI not working, check you have shunts in JMI and JMO, check the 6N138 is installed correctly… also tell us if you get the “upload request” from the sammichSID (this proves MIDI Out is working).

12

Regarding backlight, perhaps replacing the BC337 will fix this, and checking the joints for the brightness potentiometer.

Already replaced, still no backlight. I’ll check the pot.

Regarding MIDI not working, check you have shunts in JMI and JMO, check the 6N138 is installed correctly… also tell us if you get the “upload request” from the sammichSID (this proves MIDI Out is working).

Already tested and I got the upload request. I have an error message while I try to upload the firmware. By the way I have to read the forum and I have to check a couple of things… I don’t want to bother you while I’ve not tested everything twice, so it’s too soon to claim I’m in troubles.

Thanx once again for your fast answers.

13

You can start with MIDI Troubleshooting guide: http://www.ucapps.de/howto_debug_midi.html

The sammichSID base PCB has the same parts as a Core8 module, just positioned differently, with the JMI/JMO headers in series.

Feel free to ask any questions about how to do some of these tests, if it isn’t clear enough how they can be done with sammichSID.

And finally, sorry to hear you’re having such trouble - I think 95% of builds work perfectly, and yours is one of the rare cases where it doesn’t… it could be just one bad solder joint or a faulty/broken part, but it’s fixable, eventually!

14

And finally, sorry to hear you’re having such trouble - I think 95% of builds work perfectly, and yours is one of the rare cases where it doesn’t… it could be just one bad solder joint or a faulty/broken part, but it’s fixable, eventually!

Never mind Wilba, when I joined this “diy electronics” adventure I knew I was (and still I am) a complete noob with zero knowledge about electronics. The funny thing is: I started with a Shruthi (from Mutable Instruments) and everything ended right; so I gave it away as a gift and I bought another one together with the sammichSID (the sacred fire of diy was burning strong in me). The conclusion: at the moment none of the two is working hehe.

I have to improve my studies… :wink: