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cnc jim
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Join Date: Jun 2007
Location: Derbyshire UK
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Plotter Starts in 'Burn-In' Routine, and Won't 'Home'

12/03/2011 4:24 PM

Hi guys. It's the same plotter you have helped me with before, but a different problem.

A few days ago on switching on the plotter went into a burn in routine, designed to stress the components directly after manufacture. It moves backwards and forwards, knife up knife down etc. This routine is stored in rom and accessed by pressing 'left arrow' as power is turned on.

I took out the membrane switch, fiddled with the ribbon cables, hit it on the bench, and put it back. It worked for a few days.

Now I have the same problem.

I have taken the membrane switch apart so it is not being pressed. no difference.

I have disconnected the ribbon cable to the keypad PCB. No difference.

I have disconnected the ribbon cable from keypad pcb to the main logic board. The machine went into a different routine.

I figure it is the keypad PCB

My questions are; Can you confirm, comparing the parts list with the photo, that component D1 (top/mid left) is the Diiode 1N4148. (It was the brownest thing on the PCB, and when I picked at it with my finger nail it broke).

Is there any likely culprit that is saying 'left arrow key is down'? there are no components on the reverse side, and the left arrow key signal comes in 5th across from j3 bottom left

There is comprehensive info on the machine here http://www.ioline.com/support/studio7/studio7_sm_r1.pdf pages 81 & 93.

I know, it's a long shot.

Cnc Jim
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Johny451
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#1

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

12/04/2011 6:10 PM

Yes, the glass diode near C1 is the IN4148. A 100mA silicon signal diode.

They certainly don't start their life "brown" but what blew it?

Sorry can't help much otherwise.

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cnc jim
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#2
In reply to #1

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

12/05/2011 4:48 AM

Thanks for that confirmation, I'll get another put in, and see what it does. What blew it? 20 years of dioding?

CNC Jim
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Johny451
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#3
In reply to #2

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

12/05/2011 5:34 PM

Hi Jim. Diodes are not the kind of device that go brown all by themselves so it's probably handling more current than it should.

It looks like it's used in conjunction with C1 as some kind a peak hold (or any other guess). If the next diode doesn't survive I would replace C1 (Tantalum capacitor) as well. It should have it's value marked on the side.

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cnc jim
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#4
In reply to #3

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

12/05/2011 6:21 PM

Will do.

The top line as you say, goes from C1+ to the diode, the down to RP1, with a branch off to U1 near R2.

Amazingly designed, these PCB's when you look at them, but annoying for me, because they look the same broken as working.

cnc jim
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cnc jim
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#5
In reply to #4

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

01/06/2012 5:42 AM

Well, I didn't have faith that the diode would cure the machine, so I ordered a new machine, not the model I would have got if it had been planned, but an ok model, to get some work done.

I ordered some diodes, about 1p each, but the new machine was running before they arrived, and trying them wasn't as urgent.

Now in a quiet 5 mins i soldered in the new diode and fitted the panel, & the machine is back to working again! (but even top of the range 20 years old isn't as good as middle of the range now)

There's some lesson here, and when I work out what it is,.....
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Wal
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Join Date: Jun 2011
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#6
In reply to #5

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

01/06/2012 6:56 AM

Well done. You have a spare plotter now. Can you double your productivity?

Sometimes its better not to think too much. You'll only upset yourself.

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cnc jim
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#7
In reply to #6

Re: Plotter Starts in 'Burn-In' routine, and Won't 'Home'

01/06/2012 8:28 AM

Do more think less. Got it.

CNC jim
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