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Tek 7613 Vertical Slot Failure - help!


tmall@...
 

Greetings,

The middle module slot (right vertical) in my 7613 has failed. Upon power up there was smoke and the smell of a hot component after which neither vertical module will work when plugged into the middle (right vertical) position. Both modules work fine when plugged into the left vertical slot. If plugged into the middle slot it acts as if there is no vertical module plugged in, just a single trace across the zero crossing X graticule line.

I have taken the covers off and have not been able to see anything visibly scorched although there is a mica capacitor in the proximity of the back of the edge connector that looks a little dark. I have measured the +/- 15V and +/- 50V supply voltages at test points on a side PCB and found they are good there. I do not have a card extender to check the voltages on the middle edge connector but as they are common with the other two edge connectors (which are working normally) I imagine they must be OK.

Looking at the schematic I notice separate vertical slot connections to the vertical interface PCB and wonder if I should try to do some diagnostic measurements on it.

I wonder if anyone in this group has any suggestions or experience that might get me on the right track?

Thanks in advance for any help!

Best Regards,
TMA


Tom & Sylvia <tmall@...>
 

Since my first post I have confirmed that ±15V and +50V power rails are being delivered OK by the middle J2 edge connector.

This seems to only leave the vertical interface board but there is not much unique to J2 in it, just a pair of 50.5 Ohm resisters and the vertical channel switch IC. I wonder if anyone here has ever experienced an input failure of the vertical channel switch IC? Seems unlikely that only one channel would fail.

TIA!


Jerry Massengale <jmassen418@...>
 

Hi,

What vertical amps are you using? The 7A26 has a cluster of coils near the
rear connector that carry the + and - 15 and 5 volt lines. One of the coils
on the amp that was in the right slot may have some discoloration. There
was a moment of grief when you saw smoke so there may have been a short
that got cleared. A loose screw in among the connector pins can do that.
The older amps had tants on those lines. I would remove the 4 caps I am
refering to and install biased LEDs in the 4 slots. Use about 300 ohms for
the 5v lines and 1200ohms for lead bias on the 15v lines. I do not know of
a component on the backpanel that I would suspect. Good luck! I fear you
will need it.

jerry

On Thu, Nov 3, 2016 at 11:46 PM, tmall@... [TekScopes] <
TekScopes@...> wrote:



Greetings,

The middle module slot (right vertical) in my 7613 has failed. Upon power
up there was smoke and the smell of a hot component after which neither
vertical module will work when plugged into the middle (right vertical)
position. Both modules work fine when plugged into the left vertical slot.
If plugged into the middle slot it acts as if there is no vertical module
plugged in, just a single trace across the zero crossing X graticule line.

I have taken the covers off and have not been able to see anything visibly
scorched although there is a mica capacitor in the proximity of the back of
the edge connector that looks a little dark. I have measured the +/- 15V
and +/- 50V supply voltages at test points on a side PCB and found they are
good there. I do not have a card extender to check the voltages on the
middle edge connector but as they are common with the other two edge
connectors (which are working normally) I imagine they must be OK.

Looking at the schematic I notice separate vertical slot connections to
the vertical interface PCB and wonder if I should try to do some diagnostic
measurements on it.

I wonder if anyone in this group has any suggestions or experience that
might get me on the right track?

Thanks in advance for any help!

Best Regards,
TMA




[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Tom & Sylvia <tmall@...>
 

Many thanks for the info Jerry!

I dug in deeper. I found the specs on the vertical switcher chip IC, measured the voltages on its pins and discovered it wasn't getting the correct logic input for selecting the right vertical module slot. I discovered a bad connection to the vertical mode switch assembly.

Now it is apparent that the smoke and mirrors surge and right module slot failure were unrelated issues. The cause of the over current remains a mystery but I am suspicious that it may be humidity/condensation/dust accumulation related as it was in a very humid environment at the time. As I don't often use the right vertical module it is very possible it was not working for some time and I just didn't notice it.

As I sure like this scope it is certainly nice to have it working normally again!

Also great that there is a Tektronix forum for discussing issues like this!

Thanks again - this issue is now closed,
TMA