sammich sid - backlight flickering

[rbv2]

hi all,

finished my sammichSID some hours ago and it was more easy than expected.. thanks wilba!

but i have a problem with my backlight lcd. during upload of the hex file the lcd started flickering with each line of the code.(like the the code is triggering the backlight)

upload was succesfull anyways. after uploading the display is flickering randomly.. when i turn up the backlight pot. the sammichSID even reboot sometimes.

the measurementns where correct!

the psu is 12v dc 600ma http://www.reichelt.de/?ACTION=3;ARTICLE=87338;PROVID=2402

is this caused by a bad soldering?

please help me!

thanks in advance

rbv2

Edited August 3, 2010 by rbv2

[latigid on]

[latigid on]

Switchmode PSU bad?

[nILS]

[x] Switching PSU bad (way more noise, shouldn't lead to failure though)

[x] 7.2 Watts (600mA @ 12V) seems to be too little for your box. Depending on your LCD and backlight you want more oomph!

[Wilba]

12V DC 600mA should be enough... I run mine on 12V AC 500mA, with a high-power LCD.

But this is a switchmode supply? If so, no good. Something weird happens when using switchmode supplies. I have had reports of it not working with the LCD backlight. The build guide specifically says not to use a switchmode supply.

The brightness pot can be set to deliver more current than can be supplied by the recommended 12V AC/DC 500mA supply, which will cause the voltage to drop, causing the voltage regulators to also drop, causing reboots etc.

sammichSID was initially designed to work with low-power LCDs only drawing 25mA, but I put in the option of using the regular high-power LCDs that can draw up to 280mA... the problem is, an additional 280mA of current going through the 5V regulator would add a lot of extra heat to the heatsink. Using the unregulated power going into the sammichSID (i.e. the JBL header set to "12V") avoids this extra heat. Either way, though, too much current delivered to the backlight will cause the 5V regulator to "drop out" and the PIC to reboot or just stay off.

The only real solution is getting a good regulated 12V 1000mA power supply, then you can crank the brightness pot to maximum, and the voltage going into the 9V regulator will be a constant voltage (so no extra heat).

Reichelt has a good transformer based (non-swichmode) regulated 1000mA power supply... I think it was even variable voltage. It was linked to in the sammichSID thread.

[Wilba]

Unfortunately the "good" regulated 1400mA supply I linked to isn't available anymore.

Some links to power supplies which should work:

Stecker-Netzgerät, stabilisiert, 500mA (regulated 500mA)

http://www.reichelt.de/?ACTION=3;ARTICLE=64753;PROVID=2402

Stecker-Netzteil, unstabilisiert, 500mA (unregulated 500mA)

http://www.reichelt.de/?ACTION=3;ARTICLE=13273;PROVID=2402

Stecker-Netzgerät, unstabilisiert, 800mA (unregulated 800mA)

http://www.reichelt.de/?ACTION=3;ARTICLE=13285;PROVID=2402

I would probably choose the 1st one (regulated 500mA)... you would still have to watch current load, keep the brightness pot at half-way, but voltage would be stable going into the sammichSID.

The other two would work... the 800mA one might make the voltage too high going into the sammichSID when it's low current draw, but it would handle the LCD at full brightness.

[rbv2]

hey,

thank you for the numerous replies!

i bought the following psu from conrad electronics http://www.conrad.de/ce/de/product/518313/

500 mA

12 V/DC

regulated

(cant read anything about switchmode or schaltnetztei in the manual so i would say its no switchmode psu)

i connected it but the display still behaves the same way.. the flickering is totally random.. now mostly off :(

is there anything else i can check?

thanks

rbv2

[latigid on]

hey,

thank you for the numerous replies!

i bought the following psu from conrad electronics http://www.conrad.de/ce/de/product/518313/

500 mA

12 V/DC

regulated

(cant read anything about switchmode or schaltnetztei in the manual so i would say its no switchmode psu)

i connected it but the display still behaves the same way.. the flickering is totally random.. now mostly off :(

is there anything else i can check?

thanks

rbv2

No, that still looks like a switchmode one to me. You can tell because a transformer-based design will be heavy and square :ahappy: unless they use a toroid, in which case it will be heavy, flat and round. Keep searching would be my advice. Hopefully you can return some of these!

[rbv2]

No, that still looks like a switchmode one to me. You can tell because a transformer-based design will be heavy and square :ahappy: unless they use a toroid, in which case it will be heavy, flat and round. Keep searching would be my advice. Hopefully you can return some of these!

are you shure with that? to me it looks exactly like one of these psu

recommended by wilba ?

[latigid on]

I'm pretty sure man. The ones Wilba linked all look like they could fit a transformer inside. Your one doesn't. Seriously, pick it up, if it feels like nothing much more than a piece of plastic it's almost certainly a switching supply. A linear (transformer-based) supply will have some weight to it.

Another clue is multi-voltage. Switching supplies can often use a wide input voltage (100-240 VAC) whereas linear usually will need a jumper/switch changed if this is even possible.

One more clue is price. Transformers are usually more expensive than S/PSUs. I'm sure it's worth it for your little Sammich.

:)

[Wilba]

I agree with everything latigid on wrote. Test again with a transformer based supply.

[Syntax]

after uploading the display is flickering randomly.

Look simular to to problem I had, perhaps its worth checking out.

[rbv2]

I'm pretty sure man. The ones Wilba linked all look like they could fit a transformer inside. Your one doesn't. Seriously, pick it up, if it feels like nothing much more than a piece of plastic it's almost certainly a switching supply. A linear (transformer-based) supply will have some weight to it.

Another clue is multi-voltage. Switching supplies can often use a wide input voltage (100-240 VAC) whereas linear usually will need a jumper/switch changed if this is even possible.

One more clue is price. Transformers are usually more expensive than S/PSUs. I'm sure it's worth it for your little Sammich.

:)

thank you..

just to be on the safe side :)

here are the specs of the psu in detail:

Type Linear

Type regulated

1.5 - 12 V/DC

input voltage 230 VAC +- 10%

(B x H x T) 61 x 95 x 92 mm

Typ PA-500S LED

weight 370 g (its near the same wheigt as the first psu in the link wilba posted (without connectors and packing)

when i pick it up it feel like a handy brick :)

and its double the price then the recommended psu's.

so what do you think?

ps: mainly the backlight is off .. no flickering anymore.. the rest of the box is working without any problems. the reboot only occurs when the backlight is on and i turn up the brightness pot.

i also can hear a hum at the audio out which becomes louder when i turn up the backlight pot..

thanks

rbv2

Edited August 4, 2010 by rbv2

[Wilba]

I can't be sure, but reading about the PA-500S and the other models from Voltcraft, which all have different weights depending on max current, it's likely this is a transformer based power supply. They also appear to come in unregulated versions with the same weight, which also suggests it isn't switchmode.

Therefore, it should be OK.

The rebooting is expected if you turn the brightness up too much, as this PSU only delivers 500mA max. at 12V. In this respect, it would have been better to get the PA-1000S, and not have the current issue - it would always deliver regulated 12V up to 1000mA load, even at max backlight brightness.

Set the brightness pot to half-way (12 o'clock).

Is the backlight working at all now, or always off?

If you remove the shunt in JBL, do you still hear the audio hum?

If you temporarily set JBL to "5V", do you still hear the audio hum? (Don't leave it set to "5V", this is too much current for the voltage regulators/heatsinks).

[rbv2]

I can't be sure, but reading about the PA-500S and the other models from Voltcraft, which all have different weights depending on max current, it's likely this is a transformer based power supply. They also appear to come in unregulated versions with the same weight, which also suggests it isn't switchmode.

Therefore, it should be OK.

The rebooting is expected if you turn the brightness up too much, as this PSU only delivers 500mA max. at 12V. In this respect, it would have been better to get the PA-1000S, and not have the current issue - it would always deliver regulated 12V up to 1000mA load, even at max backlight brightness.

Set the brightness pot to half-way (12 o'clock).

Is the backlight working at all now, or always off?

If you remove the shunt in JBL, do you still hear the audio hum?

If you temporarily set JBL to "5V", do you still hear the audio hum? (Don't leave it set to "5V", this is too much current for the voltage regulators/heatsinks).

the backlight is working at the moment.. no flickering!

when i remove the shunt in jbl the hum is gone.. when insert the shunt to 5v also no hum.

alsways the display is not working there also is no hum.. just a silent crackle..

thanks

rbv2

Edited August 4, 2010 by rbv2

[Wilba]

I think you have a bad solder joint somewhere... probably the JBL header, or the brightness pot. That might explain the flickering, maybe the hum also.

It could be two separate issues, or combined... it sounds like when the backlight is powered by the input voltage (JBL=12V), then the extra current causes the voltage regulators not to be very stable.

Try one more thing: Insert shunts into JBP and power with regulated 12V (as before) but make sure it is tip positive. Do voltage tests on points labelled "12V"... these should now be EXACTLY 12V since shunts in JBP will bypass the bridge rectifier. This means there will be more voltage going into the voltage regulators and less likely that current load changes will cause voltage drops. Check if there is now any hum or flickering when adjusting the brightness.

[rbv2]

I think you have a bad solder joint somewhere... probably the JBL header, or the brightness pot. That might explain the flickering, maybe the hum also.

It could be two separate issues, or combined... it sounds like when the backlight is powered by the input voltage (JBL=12V), then the extra current causes the voltage regulators not to be very stable.

Try one more thing: Insert shunts into JBP and power with regulated 12V (as before) but make sure it is tip positive. Do voltage tests on points labelled "12V"... these should now be EXACTLY 12V since shunts in JBP will bypass the bridge rectifier. This means there will be more voltage going into the voltage regulators and less likely that current load changes will cause voltage drops. Check if there is now any hum or flickering when adjusting the brightness.

thanks!

ok. i soldered the trimpots and jbl header again, without success..

inserted two shunts into jbp .. the voltage on points labelled 12v are not exactly 12v! 11.40v instead. ( when i check the voltage of the psu directly on the plug its 11.50v)

when adjusting the brightness pot the hum still is getting louder! the backlight is mostly on for now but flickering still appears sometimes.

:sad:

Edited August 5, 2010 by rbv2

[Wilba]

Try removing one SID. This should reduce the current load by 100mA on the 5V supply and 25mA-40mA on the 9V supply.

I don't understand how a PSU that is "regulated" doesn't output 12V exactly at the plug. That's just a bad product. Maybe it's using some low tolerance resistors to control an internal voltage regulator... still very poor form to be half a volt less.

Right now, I still think the most likely explanation is the power supply is causing the problem, either it is switchmode, or just generally crap (not really delivering up to 600mA), or something else.

The only relationship between the backlight circuit and possible audio hum is current supply problems. When you were supplying it from the 5V supply, there was no hum. When supplying it from the input power, the load is causing the 9V regulator to not be as stable.

Do you get flickering/hum when setting the brightness pot to half-way (12 o'clock)? Do you get flickering/hum when the brightness pot is LESS than half-way?

[rbv2]

i removed one sid, now i get no sound from the audio out.. i can set the brightness pot whereever i want, no hum no flickering! (flickering is very rare at at all)

with both sids installed i get hum when the brightness pot is shortly bevor maximun.

but i cant reproduce the reboot by setting the brightness to maximum anymore..

i also have noticed a crackle noise when switching the presets without playing any sound. (with all sids installed)

just to let you know:

tomorrow im on vacation for one week so i have no chance to answer!

thanks for your help so far!!

i come back to you!

[nILS]

PSU doesn't supply enough current. Get a new/different one.

[Wilba]

Brightness should not be set to maximum anyway. I recommend no more than half-way (12 o'clock), which is why I put a BIG FAT STICKER ON THE LCD that reads:

YELLOW-GREEN high-power backlight LCD

Use shunt in JR4

Use shunt in JBL set to "12V"

Set P1 trimpot to half-way (vertical)

This is because I know this will work for 12V AC 500mA supplies, and any more than that will cause power supply issues (i.e. you will reach the 500mA limit). If you do not get hum or flickering when it is set to 12 o'clock, then either leave it there (problem solved) or get a better PSU (i.e. a regulated 12V DC 1000mA).

[rbv2]

thank you all!

maybe resoldering was not without success! bevor i did that i got

hum/flickering even with brightness pot set to minimum. i still get a little flickering

sometimes (caused by the psu) but the backlight is not totally off anymore! also the reboot seems to be gone!

:)

will get me an new psu after vacation!