We have a number of S910 monitors that all tick when in standby mode. The deal is that the monitor enters standby mode for a split second, the indicator light goes orange and then there is a tick as some relay (degausing I think), and the indicator light goes green as the flyback seems to be powering up.
There is a know issue with not powering up due to C843 and C844, but these have been replaced already. Where should we be looking for the cause of this? I already have the schematics for this monitor too.
Thanks in advance
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I don't know where the problem is. The caps on the board (inc PSU) looked OK when I was going over it before, and the monitor works fine in every other respect. Out of the dozen or so we have, 70% or more are doing this 'ticking' thing in standby mode and apparently the local repairer is familiar with this 'common problem', but won't say how to fix.
In case I wasn't clear before, when the monitor goes into standby mode, the light turns orange, half a second later it goes green with a click as everything is powered for half a sec , then back to standby mode etc... this cycles forever until the video cable is removed (no signal) or something is being output.
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The main controlling IC of the thing is dropping power when standby mode it entered. This is expected because the transformer gets turned off and hence its +5V supply. So how the heck is the thing meant to watch for sync? If I can figure this out then I should find the cause. There are only two inputs to the whole PSU circuit, one called 'OFF' and one called 'STBY', both coming from the controller IC so I assume they're both meant to go 0V when standby mode entered.
So, the logic of this as I understand is as follows:
Main IC says no sync, but grounded on the video cable, go into sleep mode...
There is 2.2V on the STBY rail when not in standby mode.
This drops to 0V and the light dependant diode (I807) stops which somehow tells the 3843B to turn off the transformer. It does, and then something (dunno what) happens to tell the 3843B to power back up. The controller IC is powered by +5V that also shuts down without the main supply.
The other OFF input holds 3V and also drops to 0V when standby mode starts. Perhaps this is where the problem is?
I guess my question is: how the heck does the thing know to wake up when there is NO power to the controlling IC responsible for turning standby mode on (and I assume off), and when there is no kind of input (no way to get input) to say wake up.
Cheers & thanks for help so far
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Standby does not stop the psu it turns it down so that loaded rails cannot keep the voltage.
The 5V should keep going as the 14V rail supplying the 5V reg I804 is probably close coupled and its load is reduced by the standby signal to Q813, this will keep the 5V rail to enable the unit to come out of standby.
With the off signal the 5V reg is supplied by the 80V rail by turning on Q809 so you should always have the 5V rail in all states.
Rich
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Well, on pin 1 of the transformer there is no voltage drop in/out of standby mode, sits about 140AC. this is same for pin 8.
On the 14.5V rail, it drops to 0V when the standby mode starts (tested from C868). The -12V rail from pin 17 tested at the rear of D818 is at -14V dropping to -12V on standby. I can't even measure pin 12 or 13 of the transformer (the source for 80V) because it does wierd things to my multimeter. Pin 10 and 11 steadily lose VDC at about .5V a sec with standby mode on, starting at 89VDC without standby.
So far its looking like the actual transformer is doing this but I don't understand how it knows when standby mode is enabled as its input doesn't really alter.
This is confusing What else should I be looking at?
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Well that is strange. R701 is measuring correctly, 100Kohm...
On Pin42's side of the R701 of the controller, without standby mode it measures about 5V. When standby mode, this drops to 2V ONLY on that side of Pin42. The other side of R701 measures 5V all the time.
Dunno what the heck I was doing before :| I was sure 5V was losing power... obviously its not, well not completely. So what would be causing the 3V drop for the controller's Vin?
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Pin 5 holds 5.01V without standby and drops to 4.70V just as standby kicks in.
On checking the input with Vin and Hin, they bot hold about 4.8V when saying there is sync I guess, this falls to 1.2V across R703 and R704. OFF and STBY are both held high (about 3.5V) until standby mode is entered, then these drop to 0V. That just seems to be doing exactly what it should.
Do you have any specs on NT6861? I want to find out how it works etc to see if its doing everything it should.
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In an effort to isolate the cause to one circuit or another I have actually removed R868 and R821 which lead to the photo dependant diodes, effectivly holding STBY and OFF to 0V for both parts of the PSU circuit, and now the monitor operates correctly. It drops into standby mode as it should, and comes out as it should.
I gather this means the cause is the controller which in itself is a problem. The main question however is how the heck does the thing wake up since I've removed the STBY and OFF inputs to the PSU. Also I'd like to know what damage am I doing by removing those 2 resisters? There is some current I've left nowhere to go now.
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Hi The standby signal only switches off the 12V which efectively shuts the monitor down by removing the scans and video drive, because there is less load on the psu it also switches in increased feedback via the opto and Q805, this adds inparallel R802 + part VR801 with R825.
You should not have too much of a problem with removing R868.
The off signal is a different story as this also connects the input of the 5V regulator I804 to the 80V rail and as you have removed R821 then Q806 can not reduce the PSU output by connecting R845 in parallel with R802, this will probably kill the 5V reg.
Your problem is their are 2 VESA states when a picture is not shown.
On = normal operation.
Stanby = no H sync but with V sync this blanks the screen and recovers to a normal picture quickly. This is your standby
Suspend = H sync on and no V sync this shuts down most of the monitor and the heaters so requires a longer recovery time. This is your off.
I belive Nutek has another scheme I am not sure what this spec is but I think there is a 4th mode possably with both syncs missing.
Rich
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Just tested without R821, at the 5V reg's side of R807, its 12.6V with OFF powered (same with R821 in), and 9.98V with OFF at 0V. Looks like that is OK for the 5V reg. I will double check all previous measurements I have to check nothing has changed...
Can confirm that all voltages the south side of the transformer are within a few V of the previous measurments when R821 was in.
Looks like this is the fix, the CRT powers down, same with the flyback and video board, which seems to be what is supposed to happen. I want to thank you very very much, removing R821 was the fix
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After putting only R821 back in, the monitor was back to its old tricks, no sitting in whichever mode it is where the indicator light goes orange that I've been calling standy... I guess its the suspend mode the monitor is having trouble entering since R868 is still out. I will put R868 back in again since it appears to not be having an impact on this problem.
At point A, when normal mode there is about 19.5V, at the point where suspend starts, it drops to less than 8V (8V was the lowest my dig mmeter caught, it only goes suspend for a split second).
I still think its the controller putting some V back into OFF and STBY. When I measured what the controller was doing (http://members.iinet.net.au/~quadfour/s1494-3.pdf), at pin 29 and 30, voltages dropped from ~3.5 to 0V on suspend start then jumped back up to about ~3.5V. On testing pin 41 (HSYNC), was 4.78V steady while tube being powered, and was a steady 1.19V with suspend mode.
Its worth noting that I am invoking suspend mode by just connecting a video card (no PC). Im certain this is invoking suspend mode. It does the same thing with a powered video card (suspended PC) anyhow.
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Some monitors may have one to two small relays that will produce a small audible momentary click when the Video Signal drops out or for a brief moment or when signal is re-applied or when the monitor is changing mode IE. 640 by 480 or 800 by 600 or 1024 by 768. This all sounds normal if it does it for a brief moment, if it does it constantly without let up when the the yellow led glows then there may easily be a small problem. Most monitors will within a moment go from green led to yellow led glow when the Video Signal from the computers video card drops signal output even if but for a short moment.
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So no conclusion to this S910 problem? I got one unit from a friend and it has the power-on problem and the standby click problem. I'd really like to know if it can be fixed.
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What else should I be looking at?