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Blockbuster dead right vu?


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#1 docs

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Posted 27 April 2019 - 09:52 AM

The right vu is not moving despite there being audio in the channel.
I’ve voltage checked comparing to the left vu and can only see less of a drop on the right channel c229 (from 1.6v approx. To 0.85v approx) against the left channel c129 (from 1.6v approx. To 0.45v approx). I’ve changed this cap which is a 4.7uf 25v but same result, slightly higher voltage at the switch on right than on left.

 

Correct voltages at IC pins 2 and 13 for right and left VU's, R136/236 check as 5.6k,

 

Anyone a clue please?

 

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#2 Reli

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Posted 27 April 2019 - 11:44 AM

Damn, this model always has dead meters, lol

Does it have a screw in the needle pivot? If so, try loosening it up a bit. Although I suspect you've already tried that.



#3 docs

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Posted 27 April 2019 - 11:49 AM

I don't see a screw no Reli. If I rattle it a bit it certainly seems to move.

#4 docs

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Posted 27 April 2019 - 12:39 PM

Maybe to test I could jump left to right? Not sure at which point but it would test the vu would move...

#5 Superduper

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Posted 27 April 2019 - 09:30 PM

The right meter works both VU and tune.  Did you check and see if any action in tune mode?  If no, then I suspect you have an issue with the meter.  Not sure why you didn't check that before posting here.  Ways to check:  1) ohm the meter and see if there is continuity.  It's merely a coil and can burn out.  2) check to see if the needle moves freely.  Like Reli says, many meters have adjustment screws for backlash.  If too tight, wont' move.  If too loose, easy to jar loose and get jammed = won't move.  If rusty or corroded = won't move.  3) apply small amount of voltage, if you have an adjustable lab power supply.  Start small, like 1/2 volts & work upwards incrementally.  I would start with the known good meter and see how much voltage it takes to elicit a response, then apply same voltage to suspected bad channel meter.

 

You checked and said meters have voltage but you checked for voltage several components down the chain, and didn't check AT the meters?  Why???

 

You indicated correct voltages at IC102.  But what IS the correct voltage, and what kind of IC is it?

 

Your measurements...  did you check with AC or DC mode?  Audio signals are AC but meter can only read DC.  



#6 docs

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Posted 28 April 2019 - 04:32 AM

The meters were voltage checked and shows the good one with around 0.10v and the bad with around 1.10v. This is where I started and then tried to find why.

Ic102 should be 1.6v. Its a “record pre amp” chip.

Only checked on AC.

I’ll open the vu enclosure and check its movement etc before testing on DC.

#7 docs

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Posted 28 April 2019 - 05:18 AM

Confirmed vu itself is shagged, no resistance across it so as you said Norm, blown.

New thread for a parts box 😩

#8 Superduper

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Posted 28 April 2019 - 08:39 AM

The meters were voltage checked and shows the good one with around 0.10v and the bad with around 1.10v. This is where I started and then tried to find why.

Ic102 should be 1.6v. Its a “record pre amp” chip.

Only checked on AC.

I’ll open the vu enclosure and check its movement etc before testing on DC.

That’s the problem, true ac meters costs a very pretty penny, so all of these meters are actually dc meters. So how do you get dc meters to read an ac audio signal? So that’s why you have the rectifiers. You shouldn’t be getting ac on the meter side if the diodes are working, maybe you should look into that and possibly why meter is blown. If NC on meter coil, that’s probably why you are getting higher than normal voltage across the meter.

#9 docs

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Posted 28 April 2019 - 08:51 AM

Yep no resistance on vu at all so probably blown as you said. The good has a reading while the bad is OL. I’ve checked all diodes and they're all good. Guess its just one of those things.

#10 Tinman

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Posted 12 November 2019 - 09:33 PM

Just some additional findings on these vu meters.
My right side wasn't working either.
What I found was that the pivot points (where the tiny screws are) are adhered to the wire windings on the front and back of the needles with little pads.
When one or both pads come unstuck they hang by some additional glue but pretty much stop working.
You can shake them and they look they're ok but they're not.
They can probably be glued, unfortunately I broke a wire in the windings right before I figured this out so mine was toast.
I ended up putting replacements in.
Fitting new ones in the original housings is a royal pita to do.
They're extremely delicate and fragile but for me, it was worth the time and effort to have them back in and working like they should.