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different versions, different schematics?


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#1 m2carb OFFLINE  

m2carb

    Combat Commando

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Posted Mon Jul 16, 2018 9:03 AM

Good morning all,

I recently picked up a Jaguar, which has C134, U38 and REG1 blown. No problem, I have replaced these before and I have added a full wave bridge rectifier and capacitor before CH1 on several Jaguar systems to alleviate this problem of the wrong polarity 9V supply being used.. This particular Jag has a blue wire from pin 1 on U11 to TP3, the full schematic I have does not show this connection. The board has a Rev J on the bar code label attached to the board.

My personal Jag has this connection with no wires, and the bar code label says Rev R2.

My question is does anyone have a different schematic than the one I am using, which shows this change on the board?

Thanks!

 

Chris L. - in Vermont



#2 Zerosquare OFFLINE  

Zerosquare

    River Patroller

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  • Location:France

Posted Mon Jul 16, 2018 2:59 PM

Can you take a picture?



#3 DEATH OFFLINE  

DEATH

    Space Invader

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Posted Fri Aug 3, 2018 6:07 PM

This seems really strange because TP3 is the test point of the video clock (and system clock), and pin 1 of U11 is its VCC power supply.



#4 Stephen Moss OFFLINE  

Stephen Moss

    Stargunner

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Posted Tue Aug 7, 2018 3:33 AM

This seems really strange because TP3 is the test point of the video clock (and system clock), and pin 1 of U11 is its VCC power supply.

 

What schematic version are you looking at? I have Document No.500162 rev 5.3 dated 21 September 1993 and Pin 1 of U11 is an output of an NOR gate (the primary output from the 26MHz clock circuit), not it's supply, which is pin 14.

Thus it would make sense for it to be connected to TP3 if the second (buffered) output of the clock circuit (U11-D) was being bypassed for some reason, i.e. its output is not functioning. If the output from U11-D is being bypassed then I would expect L32 and/or R76 to also be removed (or the tack cut) to ensure that the output from U11-D is isolated from the rest of the circuit. 


Edited by Stephen Moss, Tue Aug 7, 2018 3:34 AM.


#5 LinkoVitch OFFLINE  

LinkoVitch

    River Patroller

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Posted Tue Aug 7, 2018 4:44 AM

Thought/Question.  These odd after fab modifications, could they be the result of an assembled jag PCB failing the electrical test QA process (due to tolerances being out in components say) and then these fly-leads/ extra caps are added to rectify these minor faults?  IE tying floating inputs high or low, etc?



#6 DEATH OFFLINE  

DEATH

    Space Invader

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Posted Tue Aug 7, 2018 2:17 PM

 

What schematic version are you looking at? I have Document No.500162 rev 5.3 dated 21 September 1993 and Pin 1 of U11 is an output of an NOR gate (the primary output from the 26MHz clock circuit), not it's supply, which is pin 14.

Thus it would make sense for it to be connected to TP3 if the second (buffered) output of the clock circuit (U11-D) was being bypassed for some reason, i.e. its output is not functioning. If the output from U11-D is being bypassed then I would expect L32 and/or R76 to also be removed (or the tack cut) to ensure that the output from U11-D is isolated from the rest of the circuit. 

 

Oh yes you are right. I confused with pin 14 because the "1" is above "4" ...



#7 Stephen Moss OFFLINE  

Stephen Moss

    Stargunner

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  • Location:Cambridge, United Kingdom

Posted Wed Aug 8, 2018 3:05 AM

Thought/Question.  These odd after fab modifications, could they be the result of an assembled jag PCB failing the electrical test QA process (due to tolerances being out in components say) and then these fly-leads/ extra caps are added to rectify these minor faults?  IE tying floating inputs high or low, etc?

 

In 100% of all new units the I would say yes, in used units in 99% of all cases I would say yes as there is always the possibility that the odd used unit will be the result some amateur hacking around trying to do some mod.

 

It is virtually certain that anything which looks like it was tacked on as an after thought was added to get nonfunctioning/out of spec boards working or correct a post production design error, to just throw a non function board out would be a costly waste if taking a signal from different location or adding a resistor/capacitor can get it working.

Sometimes something as simple as buying the same device made by a different manufacture so as not to halt production can cause problems, as although the function may be the same the specification may not be. For example I designed a circuit around a 741 op-amp from National Semiconductor which worked as expected, however it did not work when I put a Phillips 741 in because despite it being an "equivalent" device its bandwidth was only 800KHz where that of the National (who IIRC developed the 741 in the first place) was 1MHz.

 

These days you would be less likely to see such things as...

a) manufacturing process have been improved resulting in fewer production errors (i.e. broken tracks) and greater uniformity between PCB's in terms of track thickness and the resulting inter layer and intertrack capacitances

b) PCB design software now includes advanced simulators and design rule checkers that ensure the PCB and Schematic connections match thus ensuring product performance and avoiding any unnoticed wiring errors before the layout is sent for manufacture.

c) Few companies bother to retain service departments as with cheaper manufacturing costs and automated electrical testing it is cheaper to throw bad boards away than to hire people to test & repair them manually.  






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