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Barco data 808s scan failure led on.

 
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Wed May 13, 2020 10:32 pm    Post subject: Barco data 808s scan failure led on. Reply with quote


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Hi I am new to forum,

I have a Barco data 808s that was built in July 1997. it has been in storage for many years and i recently decided to see if it will start up. after giving it a check over i put power on it. it looked promising the red standby led went green and all 3 tube necks are glowing dimly. however it will not power up properly, the scan failure led is lit on the G2 board also the third green Led is out. also the green led beside the scan failure led is off as well.

I checked all the boards and noticed that there was a few fried resistors and a popped capacitor on the horizontal shift board R7625035. I picked up a board (R762503) that is supposed to be working, it was fitted and still i have a scan failure led on.

I also noticed that the green led on the SMPS board is lit dimly and goes out after the projector is on for a few minutes.

I should have also mentioned that there is a red led lit on the horizontal board and also on the vertical board (this one flashes on/off at times)



Any help with this would be appreciated. Smile

Regards Tom
[/b]
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Boet




Joined: 10 Jan 2012
Posts: 30
Location: Netherlands


PostLink    Posted: Sat May 16, 2020 7:47 am    Post subject: Reply with quote

Hi Tom,

Please give us an overview of the colour status of all diagnostic LEDs (left to right?) and on which boards. They're spread out across your story now. Smile
e.g.
http://www.curtpalme.com/Barco808_Layout5.shtm
http://www.curtpalme.com/Barco808_Layout7.shtm
http://www.curtpalme.com/Barco808_Layout8.shtm

Also, could you post a detailed picture of the H-shift board and which components are fried? That could give a clue in which direction to search.
What measurement equipment do you have?
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Sat May 16, 2020 11:25 pm    Post subject: Reply with quote

Hi Boet
thanks for your reply and assistance.

Apologies if I didn't give enough information.Colour status of all diagnostic LEDs (left to right) on the G2 diagnostic board from the Tube side is led 1-on, 2-on , 3-off, 4-on, 5-on, 6-on, 7-on, 8-on (red scan failure) 9-off and 10-on (this one is away from the others).

The Horizontal outboard has red led on constant.

The vertical board has a red led on sometimes if you select input e.g s-video it will flash, if you select adjustment mode it will go out.

I did some more checking last night and found that the spring on the vertical switch for changing the ceiling to table projection has come off the switch. I managed to put it back on and it appears to be mechanically working O.K. but I would like to check it but I don't know which pins should have continuity when the switch is in or out. I am wondering could this switch have cause the horizontal shift board to fail?

The failed Capacitor is located behind the failed resistors on the lower (main board) of the horizontal shift board R7625035

I have a multimeter and an Oscilloscope, I don't have a service manual.

best regards Tom



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km987654




Joined: 25 Jul 2007
Posts: 2852
Location: Australia

TV/Projector: Barco BG809s


PostLink    Posted: Sun May 17, 2020 6:07 am    Post subject: Reply with quote

Certainly looks like a few bad parts on your H-Shift and Focus board. I have attached the Scan Fail Circuit so you can see the boards that would affect that.


ScanFailCircuit.pdf
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Scan Fail Circuit

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Boet




Joined: 10 Jan 2012
Posts: 30
Location: Netherlands


PostLink    Posted: Sun May 17, 2020 8:15 am    Post subject: Reply with quote

I've sent you the service manual over Private Message.

Now, I haven't yet looked into the status LEDs, but let's think aloud with the R7625035 circuit in front of us.

Current path around R53 (330 Ohms):
+5 V -> mosfet Q51 -> LED of opto isolator IC50 -> R53 -> mosfet Q52 -> ground.
Q51 and Q52 make some totem-pole construction, driving an opto isolator from an incoming SDA line.
The SDA line is always high when no data is transmitted, so that the P mosfet doesn't conduct and there's no current through the resistor (after the opto, the line is high again).

In order for the resistor to blow, the P mosfet must've conducted. Assuming the incoming SDA line being 5 V, this was only possible if the +5 V rail went higher than 5 V (so the the gate becomes voltage lower than the source voltage).


Else I don't really see why a 330 Ohms resistor would fry there. Even if the opto LED would be shorted, the resistor would see only about 75 mW of dissipation with 5 V across it.

Could be the 7805 started acting weirdly because of the failed capacitor and sent a higher voltage or crap (oscillations?) down the +5 V line.
With 12 V across the 330 Ohms resistor, it could slowly burn (440 mW). But this resistor burned spectacularly.
Or the resistor developed a (near-)short failure and fried itself.
Strange. Let's look further.

Now, the secondary of that opto seems to drive an SDA I²C data line again.
I would think that a failed SDA line (because of R53) simply results in a loss of communication down the chain (even gibberish aren't valid commands), instead of bad things happening. We can forget about that part of the circuit.

The +5 V does however feed some more circuits on the board, and it has diodes going to the horizontal focus coils.

Could you check if D180, D160 or D140 has failed short? That could've injected signal from the horizontal focus coil into the +5 V line, or vice versa.
That could be a cause of R53 frying and the electrolyric capacitor leaking as well.

(And might've taken IC5 (7805) along with it. If that one's shorted, likely it took the fuses in the power supply in the +FOCUS and +CONV lines.)


According to km987654 his SF diagram, SF doesn't loop through the focus + shift board. And since replacing that board didn't help, it makes me think the last option is a possibility.
There doesn't seem to be much else linked to the +5 V line at first sight.


Edit May 19th: clarified my description.


Last edited by Boet on Tue May 19, 2020 5:34 pm; edited 3 times in total
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Sun May 17, 2020 8:25 am    Post subject: Reply with quote

Thank you for the Scan failure Circuit PDF, this will be useful to help me diagnose where the problem is.
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Boet




Joined: 10 Jan 2012
Posts: 30
Location: Netherlands


PostLink    Posted: Sun May 17, 2020 9:43 am    Post subject: Reply with quote

G2 board LEDs:
third one off = no HD voltage (horizontal deflection).
8th one red = Scan Fail.
9th one off = no +CONV voltage.

No HD voltage = no HTHD voltage. Automatically disabled as a result of Scan Fail (protection).
No +CONV could be a burnt fuse, which resulted from the focus board failure. But it also receives feedback from HTHD.

Perhaps the focus board took something in the power supply along with it, we'll see.

Also measure IC5 (7805) and IC1 (7812) on the focus board.
Left - middle - right pins, text facing upwards, legs towards you: 1 - 2 - 3.
Do you measure a short between pin 1-2? 3-2? 1-3?

Tom71 wrote:

I did some more checking last night and found that the spring on the vertical switch for changing the ceiling to table projection has come off the switch. I managed to put it back on and it appears to be mechanically working O.K. but I would like to check it but I don't know which pins should have continuity when the switch is in or out. I am wondering could this switch have cause the horizontal shift board to fail?

It doesn't seem to have a direct connection to the shift board, so I doubt that for now.
Or did you find the spring loose inside the projector somewhere, so that it could've caused a short circuit somewhere?
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Tue May 19, 2020 9:34 pm    Post subject: Reply with quote

Hi Boet,

I removed the top board to give better access and now i can see that resistor R51 is Fried as well as R53.

I did some measurements on D180, D160 or D140 and they are faulty, D180 is reading .460 forward bias and 1.130 reverse bias. the other 2 are reading .480 forward bias and 1.540 reverse bias.

I also took measurement on IC5 (7805) and IC1 (7812) on the focus board.

I didn't measure a short between pin 1-2, 3-2, 1-3

Readings on IC5:
1-2 = .317, 3-2 = .753, 1-3 =.583

Readings on IC1:
1-2 = .578, 3-2 = .316, 1-3 =.592

It was many years ago when i found the spring and as far i can remember it was still hanging on the switch, however the small U shaped metal link that controls the action of the switch was missing and I only found it last week it was at the rear of the mother board near the video input connectors. when the projector failed it was mounted in the ceiling projection position so maybe this link fell into the Horizontal output board and caused a short?

it would have found it was to the location where i found it as I have moved the projector from one house to another.

I have done some quick checks and it looks like there are a number of failed diodes on the horizontal output board as well,there is no visual damage to this board.

I did check out the vertical scan switch and it is working as per the circuit diagrams so I am happy that this is o.k.

not sure what to do now, if I do manage to get another Horizontal output board will it resolve this issue or have I a voltage supply problem that is damaging the boards.

I checked all the fuses on the SMPS and G2 board and they are all perfect.

thanks for your advice.
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Boet




Joined: 10 Jan 2012
Posts: 30
Location: Netherlands


PostLink    Posted: Thu May 21, 2020 7:51 am    Post subject: Reply with quote

Tom71 wrote:
Hi Boet,

I removed the top board to give better access and now i can see that resistor R51 is Fried as well as R53.

Hi Tom, thanks. Confirms my suspicion the +5 V line went higher than it should've.

Quote:

I did some measurements on D180, D160 or D140 and they are faulty, D180 is reading .460 forward bias and 1.130 reverse bias. the other 2 are reading .480 forward bias and 1.540 reverse bias.

The diodes sound OK.
.480 forward is quite low, looks like your multimeter uses very low current in diode mode (micro Amp range).
This might give false readings in reverse bias, since small leakage would easily be detected as 'conduction'.

Anyhow, I think we could rule these parts out for now.

Quote:

I also took measurement on IC5 (7805) and IC1 (7812) on the focus board.

I didn't measure a short between pin 1-2, 3-2, 1-3

Readings on IC5:
1-2 = .317, 3-2 = .753, 1-3 =.583

Readings on IC1:
1-2 = .578, 3-2 = .316, 1-3 =.592

No shorts, good. But determining whether the 7805 and 7812 are OK is difficult this way. I've just measured multiple good ones, various brands, all read differently.
So I can't give a conclusion about those yet.

Could you measure the voltage on the +5 V line on the focus/shift board, with the projector turned on?
Just pick a node which is easily accessible - e.g. cathode of D50 (+5 V), and one of the many grounds.
Even easier if you have a bench power supply: board on the table, feed 17 V to the input of the 7812.

Quote:

It was many years ago when i found the spring and as far i can remember it was still hanging on the switch, however the small U shaped metal link that controls the action of the switch was missing and I only found it last week it was at the rear of the mother board near the video input connectors. when the projector failed it was mounted in the ceiling projection position so maybe this link fell into the Horizontal output board and caused a short?

That's possible, the Scan Fail line runs through the Horizontal deflection board.

Some options:

It could've dropped between the +5 V line and a higher voltage line (12 V / 17 V?) on the focus/shift board.
That would toast the resistors, but the 78xx will survive up to 7 V reverse bias. Wouldn't explain the failed capacitor.
This +5 V line is both created and used only on the focus board, wouldn't explain the scan fail.
-----

But, it also could've bridged the machine its +17 V line to a higher voltage line. Let's hope not, that could've fried lots of stuff on other boards connected to +17 V.
Would be strange as well.

-----

Different option, maybe I'm fixated on the wrong thing: what if the capacitor and both resistors had failed earlier already (and are unrelated to the metal part which got loose and Scan Fail error)?
If you never had to change the shift settings after R51 and R53 had burned out, you wouldn't have noticed that had happened.
But +5 V also clamps the focus, maybe you would've noticed something there.

Quote:

I have done some quick checks and it looks like there are a number of failed diodes on the horizontal output board as well,there is no visual damage to this board.

Which ones, and what's their reading?

Quote:

not sure what to do now, if I do manage to get another Horizontal output board will it resolve this issue or have I a voltage supply problem that is damaging the boards.

You wrote you exchanged the focus/shift board (R7625035) with another (R762503). I don't know if these are interchangable?

Looks like either the "Horizontal deflection" or "Vertical deflection & sync" board is indeed pulling the Scan Fail line to ground
(either because of a failure on those boards themselves, or missing a signal from another board).


To check whether the H/V deflection board triggers Scan Fail:

Vertical deflection board, is D461 lit? Then the Scan Fail originates from the vertical deflection board.

Else it's the horizontal deflection board, triggers scan fail in case HDH_R, HDH_G or HDH_B is missing.
These HDH signals come from the horizontal shift / focus board.
(The base of Q15 will be high (around 0.6 V), but difficult to measure inside the set.)

Quote:

I checked all the fuses on the SMPS and G2 board and they are all perfect.
thanks for your advice.


Ok Thumbs Up The problem with a loose part: it could've bounced anywhere.
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km987654




Joined: 25 Jul 2007
Posts: 2852
Location: Australia

TV/Projector: Barco BG809s


PostLink    Posted: Fri May 22, 2020 4:06 am    Post subject: Reply with quote

Make sure that the vertical switch that has the spring missing is in the right position. If its table mounted then it should be all the way in.
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Sun May 24, 2020 9:05 pm    Post subject: Reply with quote

Hi Boet

I cant' find D461, there is a D20 led lit on the vertical board, it will flash if you select adjustment mode and will stay on constantly if you select source e.g s video

and also D10 is lit on the horizontal output board. I soldered some test wires on the horizontal output board so I could test the board for power while it is in the projector 17v is present on board, also 12v is present on IC4 and 5v is present on IC5.

I will measure the voltage on the +5 V line on the focus/shift board, with the projector turned on.

Also I may have jumped the gun on finding bad diodes on the Horizontal output board, you were right about my multi-meter, it was giving me strange readings so I am using a different one and the diodes look o.k now so that is good.



I wonder if I have created another problem by using the (R762503) board instead of the original focus/shift board (R7625035) I was told by the seller that this board was working fine. does anyone know if there are interchangeable.

I read in another post that the projector should start with the focus shift board removed from the projector, but the image will be all over the place.

I will keep checking, when i get a chance.

thanks Very Happy


Last edited by Tom71 on Sun May 24, 2020 9:17 pm; edited 1 time in total
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Sun May 24, 2020 9:09 pm    Post subject: Reply with quote

km987654 wrote:
Make sure that the vertical switch that has the spring missing is in the right position. If its table mounted then it should be all the way in.


Thanks, I managed to get the spring back on the switch and I tested the pins outs according to the circuit diagram and the switch is working 100% Regards Tom
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km987654




Joined: 25 Jul 2007
Posts: 2852
Location: Australia

TV/Projector: Barco BG809s


PostLink    Posted: Mon May 25, 2020 9:21 am    Post subject: Reply with quote

Tom71 wrote:
Hi Boet

I cant' find D461, there is a D20 led lit on the vertical board, it will flash if you select adjustment mode and will stay on constantly if you select source e.g s video

and also D10 is lit on the horizontal output board. I soldered some test wires on the horizontal output board so I could test the board for power while it is in the projector 17v is present on board, also 12v is present on IC4 and 5v is present on IC5.

I will measure the voltage on the +5 V line on the focus/shift board, with the projector turned on.

Also I may have jumped the gun on finding bad diodes on the Horizontal output board, you were right about my multi-meter, it was giving me strange readings so I am using a different one and the diodes look o.k now so that is good.



I wonder if I have created another problem by using the (R762503) board instead of the original focus/shift board (R7625035) I was told by the seller that this board was working fine. does anyone know if there are interchangeable.

I read in another post that the projector should start with the focus shift board removed from the projector, but the image will be all over the place.

I will keep checking, when i get a chance.

thanks Very Happy


They are interchangeable. the 35 is just a later version.
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Tom71




Joined: 13 May 2020
Posts: 7
Location: Ireland


PostLink    Posted: Mon May 25, 2020 10:12 pm    Post subject: Reply with quote

Thanks for the info on the board interchangeability, yes the date on the older board is 1996 and the the 35 is 1997.I will have another go at diagnostics at the weekend 👍
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Boet




Joined: 10 Jan 2012
Posts: 30
Location: Netherlands


PostLink    Posted: Sat May 30, 2020 10:25 am    Post subject: Reply with quote

Tom71 wrote:

I cant' find D461, there is a D20 led lit on the vertical board, it will flash if you select adjustment mode and will stay on constantly if you select source e.g s video

Which R... board do you have? I was using the R7628085-3 / R781121-3 schematic, and I don't see D20.

Quote:

and also D10 is lit on the horizontal output board.

That one's "Deflection hold down".
It will light up under these two fault conditions:

D10 is on the middle-right of the schematic (R76226715_0_Diagrams).
If either pin 7 of IC6, or pin 7 of IC3 is pulled to ground, D10 will light up. Also DEFL_OFF gets pulled low, shutting down deflection (circuit is on the next sheet).
This is the case if HDL_REF gets higher than LIN_REF (IC6), (likewise if LIN_REF gets lower than HDL_REF).
Or when pin 6 gets higher than pin 5 (IC3), that's when the 1900 V set by P2 gets too high (overvoltage protection).
The second situation cannot happen if the first situation is active (no deflection = no possibility for overvoltage across the scan coils).

To be sure, measure pin 5 and 6 of both IC3 and IC6, referenced to board ground.

Now, judging quickly, looks like this fault conditions can occur if H_DRV signal is missing (comes in from the Sync & vert. def. board).
If LIN_REF is lower than HDL_REF, measure with an oscilloscope if there's signal on H_DRV (page 3 of R76226715_0_Diagrams, left-bottom side).
You can solder a wire to the input capacitor again for that, the signal will be under 100 kHz.

If there's no signal at H_DRV, the problem is likely on another board (on/via Sync & vert. def.). If there's a signal on H_DRV, a fault on the hor. def. board is likely.


And as a result of above fault(s) -> no deflection -> scan fail is also triggered.

Quote:
I read in another post that the projector should start with the focus shift board removed from the projector, but the image will be all over the place.

Sounds plausible, we can shift our focus then. ( Wink )

Quote:

I soldered some test wires on the horizontal output board so I could test the board for power while it is in the projector 17v is present on board, also 12v is present on IC4 and 5v is present on IC5.

Good.

---
What could've happened on the shift board: 5V is connected to the focus coils as a sort of 'voltage clamp' it seems.
The way I see it, every cycle a peak current will be pulled from the 5V line (ripple current). This will wear out the electrolytic capacitor more quickly than usual.
With the el. cap. failed, the 7805 might've got unstable, frying the resistors.
But since you have a replacement board, repairing the focus board's not yet a priority.
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