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Its me again.. (PSU LVDD voltage drops when connected to γ3

gamma3, gamma24 (plug-in for the γ3)

Its me again.. (PSU LVDD voltage drops when connected to γ3

Postby Balcmeg » February 16th, 2017, 1:04 am

Hi Ti,

I was updating mu Gamma3 PSU when the 5V LVDD tore loose and probably got to LVDDs ground, not 100% certain there.
The PSU is working fine, until I connect it to my Gamma3. Yes I screwed up again.

When J12 is unconnected I have +5V there but when I connect it to the main board the voltage drops to ca 2,7V. If I disconnect ALL Molex connectors to the LCDuino, I have ca 4.2V over J12s connectors, seems like I fried things on both LCDuino and on G3 board, just hoping its not the zeta again..

On Duiono the display don't lit up of course, but the Blue LED is lighted dimly - that should be LEDP.

Ill go and do some more basic testing, but do you have any obvious suspects - or any that can be excluded- On the main board should not be many circuits that can be the problem.

EDIT:
I measured when Zeta1 was removed than the numbers are the same.
/Stefan
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby amb » February 16th, 2017, 2:33 am

Disconnect the PSU from the load at its output terminal. Connect a resistive load (e.g., 20 ohm 5W resistor, the exact resistance does not matter as long as it's something in the neighorhood). This should create a 250mA load, if a 20 ohm resistor is used). Measure the output voltage to see if it could maintain the 5V output. If not, then the problem is in the power supply. Otherwise, look further downstream.
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby Balcmeg » February 16th, 2017, 4:32 am

Fortunately I had a couple 22ohm/10W at home. Connected direct on the Phoenix terminals on the Sigma11 and the voltage is only 0.9V, when i remove the resistor it go back to 5.05V.

Obviously its the Sigma11 that the problem and not in Gamma3. I'ts the new one i built to replace the Sigma25 I used previously, I forgot that I didn't have a suitable transformer at home to test it with at the time it was built and installed it anyway.

Its a bit late here now, but tomorrow I will start checking polarities on diodes, resistor values etc.
/Stefan
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Its me again.. (PSU LVDD voltage drops when connected to γ3

Postby amb » February 16th, 2017, 4:36 am

Check the actual resistance of the two 0.47Ω 2W metal oxide resistors. They are probably the wrong value, or had been blown by a short circuit at the output.
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby Balcmeg » February 16th, 2017, 4:47 am

amb wrote:Check the actual resistance of the two 0.47Ω 2W metal oxide resistors. They are probably the wrong value, or had been blown by a short circuit at the output.


Don't really wanna tell you.. but they are 470ohms.. must have ordered the wrong type last time.

I have 4 pcs 1ohm/2W at home. If i remember right I cant get the .47 ohm from RS.
I can parallell 2x1 ohm instead its close enough.
/Stefan
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby Balcmeg » February 16th, 2017, 5:41 pm

Ok, i changed resistors this morning and all is working fine.Thanks for the help - again!

Two questions though:

1) When i put together the PSU the first tome, RS didn't have the SSR you recommend in the Parts list and instead I used another Omron SSR with 220V/2A max current.
This SSR is for PCB mounting, so i put it on a experimental board. Question is - apart form aesthetics, is there any problem with as low as 2A max current? Its been working so far and on Gamma3 site minimum current is stated as 300+400mA through the SSR, so if max current don't deviate much from the min current I assume I am ok?

2) I normally run my Gamma3 with display off so I plan to change the *mute* switch to one similar but with built in LED that I already have around - same model that I use for my power amp and other equipment. Where would be the best place to tap the voltage for the LED? Instead of LCDP on LCDuinos board?
/Stefan
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby amb » February 16th, 2017, 10:08 pm

Balcmeg wrote:1) When i put together the PSU the first tome, RS didn't have the SSR you recommend in the Parts list and instead I used another Omron SSR with 220V/2A max current.
This SSR is for PCB mounting, so i put it on a experimental board. Question is - apart form aesthetics, is there any problem with as low as 2A max current? Its been working so far and on Gamma3 site minimum current is stated as 300+400mA through the SSR, so if max current don't deviate much from the min current I assume I am ok?

The 2A rated SSR should handle normal operating conditions just fine, but at turn-on time, the surge current to energize the transformers and charge the capacitors may exceed that rating. But then those SSRs should be able to take a higher load for a short duration...

2) I normally run my Gamma3 with display off so I plan to change the *mute* switch to one similar but with built in LED that I already have around - same model that I use for my power amp and other equipment. Where would be the best place to tap the voltage for the LED? Instead of LCDP on LCDuinos board?[/quote]
GVDD or AVDD with an line resistor.
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby Balcmeg » February 16th, 2017, 10:24 pm

amb wrote:
Balcmeg wrote:1) When i put together the PSU the first tome, RS didn't have the SSR you recommend in the Parts list and instead I used another Omron SSR with 220V/2A max current.
This SSR is for PCB mounting, so i put it on a experimental board. Question is - apart form aesthetics, is there any problem with as low as 2A max current? Its been working so far and on Gamma3 site minimum current is stated as 300+400mA through the SSR, so if max current don't deviate much from the min current I assume I am ok?

The 2A rated SSR should handle normal operating conditions just fine, but at turn-on time, the surge current to energize the transformers and charge the capacitors may exceed that rating. But then those SSRs should be able to take a higher load for a short duration...

Yes, its been working for some year in total without any trouble as far as I noticed. I guess I keep it as it is for now and exchange later on - maybe.

All I have at home except this one is an old Surplus Kodak SSR - 40A and I don't have other specs for it. I doubt It can work with this small, inductive load.

amb wrote:
Balcmeg wrote:2) I normally run my Gamma3 with display off so I plan to change the *mute* switch to one similar but with built in LED that I already have around - same model that I use for my power amp and other equipment. Where would be the best place to tap the voltage for the LED? Instead of LCDP on LCDuinos board?

GVDD or AVDD with an line resistor.

I actually put a 3pin Molex header on LCduinois main board in the place where C2 would have been if the real-time clock were installed. I had to cut the middle pin and the outer two pins fit perfect there. I then soldered the load resistor between the empty pads 1 and 8 where U2 would have been.
/Stefan
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby amb » February 16th, 2017, 10:32 pm

Balcmeg wrote:I actually put a 3pin Molex header on LCduinois main board in the place where C2 would have been if the real-time clock were installed. I had to cut the middle pin and the outer two pins fit perfect there. I then soldered the load resistor between the empty pads 1 and 8 where U2 would have been.

Those are not power pins, and even if they were, the LCDuino-1 is always on. The one place on the LCDuino-1 where you can get a voltage only when the power is on is the SSR trigger line.
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Re: Its me again.. (PSU LVDD voltage drops when connected to

Postby Balcmeg » February 16th, 2017, 10:45 pm

amb wrote:
Balcmeg wrote:I actually put a 3pin Molex header on LCduino's main board in the place where C2 would have been if the real-time clock were installed. I had to cut the middle pin and the outer two pins fit perfect there. I then soldered the load resistor between the empty pads 1 and 8 where U2 would have been.

Those are not power pins, and even if they were, the LCDuino-1 is always on. The one place on the LCDuino-1 where you can get a voltage only when the power is on is the SSR trigger line.


Did i misread the schematics for LCDuinio?
Pin 1 on U2 is connected to +5V and pin 8 is connected to C2, the other pad on C2 is connected to Ground so with load resistor between pin 1 and 8, and then the LED connected where C2 would have been it should work?

My intention was to see when the power is on on the PSU, not when Gamma3 is on. I have installed a Switch on the PSU that allow me to power it off completely when I ma away from home longer times. Our building is old and the electrical wiring of Hong Kong standard, during two months last year the fault-current breaker released daily for no reason and letar it just went back to normal. We had people over to check and all thay said was its released because there is some problem but the breaker works as it should... what the probolem was they couldn't tell. Turning on/off the microwave result in a nice pop from the speakers, so we know when the food is hot. :)

Sometimes I miss Sweden, but mostly not.
/Stefan
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