8mm Forum: HELP my GS1200 is ILL

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Posted by Robert Aragon (Member # 181) on June 09, 2007, 02:59 PM:

Where , Oh where Do i send my projector for repair? In san Diego california here. The problem began with Static being recorded when i used the sound on sound knob. Then, i noticed it wouldnt erase some tracks properly..then, one day. The projector motor didnt start....I thought. hmmmm. I turned it on, returned later, and started fine. Now, stopped again, IF i turn off, unplug and restart it, it may or may not turn on. What can be the problem? I havent recorded much with this projector,should, i attempt to "fix" myself? Or send away? i KNOW ABSOLUTELY nothing, when it comes to electronics..wish i did. To reiterate...help!
sincerely, in mourning, Rob

Posted by Kevin Faulkner (Member # 6) on June 09, 2007, 05:02 PM:

When you say static I take it you mean a crackling interference noise?
This could be the same problem another member has had on the forum recently. It could be down to some diodes which get very hot on the main circuit board. These 3 diodes are in series with the main motors -ve supply and get very hot while the motor is running and can eventually give dry joints.

Did you get any instances before when the motor might loose control and not run at the right speed? or got intermittent. Does the motor run ok when the machine is cold?

The reason I ask these questions is that the fault condition I talk of doesn't tend to just happen but gradually get worse as time goes by. (Think I can hear a song coming on here) [Big Grin]

Do you know someone close by to you with another GS? If you do and they are willing I would suggest you remove your motor (very easy) and simply plug it into their machine to check it isn't the motor thats at fault.

Kev.

Posted by Robert Aragon (Member # 181) on June 09, 2007, 10:11 PM:

Hi Kev, Did you get any instances before when the motor might loose control and not run at the right speed? or got intermittent. Does the motor run ok when the machine is cold? THE ANSWER IS YES, now come to think of it,t here was a SPEEDING up moment, then it stopped...I FORGOT ABOUT IT. YES, the projector runs fine when it is cold. Does this sound familiar?
Rob

Posted by Kevin Faulkner (Member # 6) on June 10, 2007, 06:21 AM:

Yes that sounds a bit like the diodes to me. Are you into removing the back and doing a visual check on the main circuit board?

Posted by Robert Aragon (Member # 181) on June 10, 2007, 09:43 AM:

I'm willing to learn and try anything(i know i can, i know i can).

Posted by Kevin Faulkner (Member # 6) on June 10, 2007, 05:33 PM:

OK. Had a busy weekend but tomorrow eve I will take some pics of the area on the main board where you need to look for scortching marks.
You could in the meantime just take the back off and then turn the machine upside down so that you can view the underneath of the main circuit board. Right in the centre of the board you should check to see if there are some solder joints which look brown.

As I say I will take some pics showing exactly where you should look but having said that if you have a look in the meantime it should be quite obvious if you have this problem.

Kev.

Posted by Robert Aragon (Member # 181) on June 11, 2007, 03:17 AM:

WOW Kevin..there is excitement and nervousness.AS ALWAYS, thanks for HELPING us...your amazing. yrs, Rob

Posted by Robert Aragon (Member # 181) on June 16, 2007, 10:38 PM:

Does anyone know of SOMEONE who can repair my GS 1200? I am in San Diego, thanks, Rob

Posted by Kevin Faulkner (Member # 6) on June 17, 2007, 04:46 AM:

Is that a reminder that I forgot to send some pics.....naughty me.

Will do this for you later today.

Kev.

Posted by David Evans (Member # 482) on November 15, 2010, 05:20 PM:

Hi

Back in June 2007 Kevin mentioned the three diodes which are in series with the main motor, the ones which get hot when it operates. Around then I bought a GS1200 on eBay and had just the problem that he mentioned, except that the problem was not dry joints but an open-circuit diode. The result was a fried 100 ohm resistor (the one that by-passes the diodes) and the 270 ohm one which connects with the lamp relay driver. I replaced the resistors and the diode (with a 1N4007 - similar spec to the 1S1887 used originally) and all was well. Except that it has just repeated the fault! Again fried resistors and a diode (not the new one) open circuit. This time I have mounted three new diodes underneath the main PC board on slightly extended leads so that they have more air flow and hopefully the soldered joints will run a little cooler.

My question - is this a common fault with GS1200s, or have I been unlucky? Are 1S1887s prone to going O/C?

Personally, I don't like running around the maximum rated current through diodes (1A peak, 800 mA max recommended continuous, which is getting on for what the motor draws). As an ex-Miltary electronics development engineer, personally I would have put something like a 1 ohm resistor in series with the motor and sensed the voltage across it with a transistor. It would have achieved the same end (stopping the lamp from working when the main drive motor isn't).

Thanks for any comments.

Posted by Bill Parsons (Member # 244) on November 17, 2010, 11:14 AM:

David,
I agree with you these diodes are not really man enough for the job, I often fit 1N5408 diodes, these are rated at 3A and never give a problem , it saves the pcb getting burnt, I fit these diodes on a separate small pcb, this you can fit in any convenient position in the projector.
Having said this, if the motor is drawing excessive current, (motor will run hot) this can cause the problems with the diodes.

Bill.

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