spc900 lx mod problem help

[starship trooper]

hi there,

I have just finish my lx and amp off mod and linked the camera to my pc to try it out with the original lens on and the picture is bad very grainy couldnt make any detail out on anything and i also tried it in the dark couldnt make out much but the picture was a bit better here are some pics.

here are some pics of the board

I used the methord off of the bolton astro club sitehttp://www.boltonastro.org.uk/Members_Area/Projects/spc880conversion.pdf and also a lot of info off of this thread http://stargazerslounge.com/diy-astronomer/134194-webcam-mod-wiring.html

i dont know if i have the diodes the wrong way round maybe or maybe the transistors heres a pdf for them http://www.datasheetcatalog.org/datasheet/philips/BFY50.pdf?is it ok that i have used 2 different transistors?

The serial cable d9 plug i wired the dtr to pin 4,ground to pin5 and rts to pin 7 is that right?

Is there any test i can do to see why this isnt working?

All the help would be appreciated thank you dazz:confused:

[mrmoo]

Blimey that's some diode you got in there, sorry I know that's no help.

Do you have a multimeter? There are a few voltages to check that signals are present and in the right place.

[starship trooper]

Yes I thought that when I saw it ,i do have a multimeter

[mrmoo]

To check the function of the circuit, when switching from standard mode to LX make sure 5vdc is appearing on the RTS/DTR diodes. After that check the zener goes low from 15.4vdc to around 11vdc and the 8/13 transistor base goes from 3.3vdc to zero.

[Domis]

maybe check the pin orientation of the transistors,there are two types EBC and CBE the BFY50's I believe are EBC can't tell what the other is.If it is a 2n3904 or BC548 or other.Best to look up data sheets [google] to find out.If is reversed you can just turn them around.On the schematic the pin with an arrow head is the emitter pin.

[Domis]

In Bolton's mod he used BC548 transistors I could only find at a local electronics retailer the 2n3904 transistors and they are the opposite pin orientation so I had to reverse them.Hope you get up and working.

[mrmoo]

It makes no difference or mix of signal transistors used tbh. So long as they're orientated correctly. If for some reason the circuit isn't switching the cam just acts in normal mode. Not sure what's going on there, check the voltages as I said. All else fails check you haven't shorted the cam out. Back to basics, disconnect the pad/pin wires. Short the pairs out and check the cam functions normally.

[starship trooper]

The other transistor is a bc548 on boltons schematics it sent show the emiter pin also when I check the transistor which pin do I put the red meter lead to and what side do I put it on the diodes? To test this do I turn on and off lx mode in the pc program? And do I kedo the black meter wire on the earth side of the board when testing?

When it is on normal mode the pictures are the same as what is shown.

Could having the pin/pad wires the wrong way around have this effect?

Sorry for all the questions I just hope I havent messed it up

[malc-c]

Looks to me as if the frame sync is screwed up... can't really add to what's already been said, other than I would suggest using three of the same type of transistors (2N3904 are ideal) and check the orientation.

Check the correct pad to pin connections and look for continuity of the GND between the Serial port and USB

[mrmoo]

The other transistor is a bc548 on boltons schematics it sent show the emiter pin also when I check the transistor which pin do I put the red meter lead to and what side do I put it on the diodes? To test this do I turn on and off lx mode in the pc program? And do I kedo the black meter wire on the earth side of the board when testing?

When it is on normal mode the pictures are the same as what is shown.

Could having the pin/pad wires the wrong way around have this effect?

Sorry for all the questions I just hope I havent messed it up

Black lead goes to the negative connection on the board, check continuity back to the cam and the screen of the serial port. Check the voltage on both sides of the RTS/DTR diodes, switch the control signal on and you should +ve appear on both sides of the diode. Check the voltage on the far left transistor base (middle), you should see something like 3.3vdc drop to zero when the RTS control signal comes on. Check the output voltage of the zener (after the cathode marked side) or at the Q3 base wire watch for a drop to 11v or so when the DTR is switched on.

Routinely you'd want to check all those things on any newly modded cam. Like I said, to be sure make sure the cam is working normally detached from the control board. First place I'd look and my money would be on a short at the cam side, you've used quite large wire it would be very easy to bridge something accidentally.

[Domis]

Can you post a pic of the underside of the board so we can follow your circuit better?

[malc-c]

Looks like the resistors are the wrong values. Hard to tell which way you read them, but it could be Brown, Black, Black = 10 ohm, or Brown, Red, Black = 12 Ohm. - don't look like 10K (Brown, Black, Orange) to me

[mrmoo]

Brown, Black, Black, Red, - Brown = 10kΩ 1%

Green, Blue, Black, Gold, - Brown = 56Ω 1% (although there's no fan so that and the suppressor diode it's kinda superfluous.)

[Domis]

looks like the 56k resistor was moved to a new location on the pcb board before mounting in the project box ,could be an error in the connection there.

[Domis]

Malc-c or Mrmoo is there any way to test this circuit without attaching to cam or computer, just a power supply?

[RogerTheDodger]

I got a view like your second pic as the wires to the pin/pad bits were crossed over, switched them back and it was fine... double check or try it

[starship trooper]

The resistors should be 10k and the 56k is there for a fan I just havent fitted it yet,the pad and pin wires might be the culprits because I was working from 2 different schematics,

I shall get pic when I get home and I am going to test the camera and join the pad/pins.back up and check for shorts.

All the help is.much appreciated thank you very much

[malc-c]

Brown, Black, Black, Red, - Brown = 10kΩ 1%

Green, Blue, Black, Gold, - Brown = 56Ω 1% (although there's no fan so that and the suppressor diode it's kinda superfluous.)

Never could get the hang of the 4 band coding

[mrmoo]

the 56k is there for a fan I just havent fitted it yet,

The value of the resistor should really be chosen on the fans current and the voltage drop you want. The 5v fan's I use don't need slowing imo and they don't take a lot less before they stall. You may be fine, but don't be surprised if you need to change the value. 0.06A 5v fan will drop to around 3v with a 56R @ 0.07W so 500mw is more than enough.

[starship trooper]

well i have just tried the camera with the pins and pads connected together and it worked fine so there is a problem with the lx board here are some pic sorry the messy wiring hope you can point to the problem

as for the connection of the pins/pads to the board i had the yellow and blue wires going to pad/pin 10 (shutter) and the red and white wires goto the 8/13 (gate) is that correct?also i wired the switch between the pad/pin 10 is that correct?

please refer to this schematic

Cheers dazz

[mrmoo]

Just trying to follow it all.

Ok, your white (PAD8/13) should go to the side with pins sticking out. Same goes for the rest, all back to front.

Swap red for white and blue for yellow.

[starship trooper]

right i have just changed the pan/pin wires around so the ones i had going to the pad/pin 10 are now connected to pad.pin 8/13 and when the switch is in one position the pictures normal but when i flick it the other way the picture flickers alot and now and again the picture will become clear i have look to see if there is a short but cant find anything.

[starship trooper]

also i when i first made up the serial cable i solder the shelding to the d9 plug and then i have soldered the other end to the green earth wire of the serial cable is this ok? didnt know whether it would interfer with it at all?

have i got the switch wired up right?

Cheer dazz

[mrmoo]

right i have just changed the pan/pin wires around so the ones i had going to the pad/pin 10 are now connected to pad.pin 8/13 and when the switch is in one position the pictures normal but when i flick it the other way the picture flickers alot and now and again the picture will become clear i have look to see if there is a short but cant find anything.

If I read that right then nope. Where you had the white swap it for the red, and the yellow for the blue.

also i when i first made up the serial cable i solder the shelding to the d9 plug and then i have soldered the other end to the green earth wire of the serial cable is this ok? didnt know whether it would interfer with it at all?

have i got the switch wired up right?

Cheer dazz

With two core screened, the shielding should go to pin 5 on the DB9, the other end of the screen goes to the negative. There's no need to connect the signal to the protective ground. Switch looks ok, next time I'll donate you one of my kits it'll be quicker, only kidding. You'll get there.

[Domis]

I see a problem with the fan circuit,I don't know if that would hurt as it is not being used.There should be a track cut between the legs of the 56k resistor and the diode should be connected after the resistor.I am no electronics wiz so better check with someone more knowlegable before changing.