Vu meter sticky after some use...

[frenkonio]

°°° Calling all vu meters experts! °°°
Anyone knows what could be the issue in a vu meter that starts working ok (I mean, it is "bouncy" as it should when working) then after 40/50 minutes becomes a bit sticky and you have to tap on the glass to bring it back to where it should be?
I'm going nuts (it's a HOYT 597 meter). I opened it looking for dust or debris, no way. I've noticed it has a small pcb behind with some resistors and maybe a couple of diodes.
If you let the unit cooling down for an hour and switch it on again then the vu is working again... mistery!
Would love to understand where to begin troubleshooting. I swapped the connector with the other vu meter (that always works, even after hours) and it's still acting funny with all the electronics of the other channel.
Appreciate who could point me in a direction!

 

[sodderboy]

Is it new?
How hot does it get to need to cool down?
Can you see the needle touching the front glass or the scale (hardly ever with new meters)?
There can be static electricity with some meters, plastic or glass, where they will hang up with no signal, and the fix is to gently move your fingers over the face of the meter touching it and chassis metal, and the needle drops.
And the static issue was usually only with consoles, I cannot remember an issue with outboard. Could there be a DC bias building-up in the VU circuit? That can be measured at the terminals.
Mike

 

[industrialarts]

Not sure if this is applicable in your case, but I have come across the problem of the red glue used fix the 'zero' trim migrate and get sticky. jamming up the meter. There was a post on YouTube somewhere, the tech used a tiny bit or acetone to loosen up/ remove a bit of the glue. It did work for me on the meters that use that type of fixative
Perhaps the bulbs heat the glue up enough to make it sticky and when the meter cools the glue hardens and recedes. Again, this only works on certain types of meters.

 

[frenkonio]

Not sure if this is applicable in your case, but I have come across the problem of the red glue used fix the 'zero' trim migrate and get sticky. jamming up the meter. There was a post on YouTube somewhere, the tech used a tiny bit or acetone to loosen up/ remove a bit of the glue. It did work for me on the meters that use that type of fixative
Perhaps the bulbs heat the glue up enough to make it sticky and when the meter cools the glue hardens and recedes. Again, this only works on certain types of meters.

There's no bulb inside but two simple amber leds that don't get so much hot to melt the glue unfortunately... this was a clear fix on old meters, this has 5 years and it's from HOYT (a 597 model), moving coil.

 

[frenkonio]

Is it new?
How hot does it get to need to cool down?
Can you see the needle touching the front glass or the scale (hardly ever with new meters)?
There can be static electricity with some meters, plastic or glass, where they will hang up with no signal, and the fix is to gently move your fingers over the face of the meter touching it and chassis metal, and the needle drops.
And the static issue was usually only with consoles, I cannot remember an issue with outboard. Could there be a DC bias building-up in the VU circuit? That can be measured at the terminals.
Mike

The needle doesn't touch the glass, is way far from it. I thought about static too but the problem is that the vu meter works ok for the first 40/50 minutes, then it gets more slow in movement (or sticky if you prefer) and everytime you switch from Gain Reduction to Output or other functions it never goes where it should. If you pick three times on the glass it goes where it should be. Switch off the unit, let it cool for an hour and it comes back working perfectly. At this point I think there's something involved in the small board behind the meter with the rectifier circuit.

 

[Brian Roth]

Ask Hoyt (a long-time manufacturer) what ideas they may have???

Bri

 

[Philbo King]

Try freeze spray on various components when it happens.

 

[frenkonio]

Ask Hoyt (a long-time manufacturer) what ideas they may have???

Bri

That's what I did, the first time they were talking about dust and debris, I checked them opening the vu and there was no dust or debris. Assembled it again and it had the same issues as before. Now I asked more hints, the vu has a small pcb board behind with some resistors and diodes (I suppose it's the rectifier board), probably something failed there.

 

[gyraf]

dismount the pcb while in err-mode, that'll tell you at which end the error is located

 

[frenkonio]

dismount the pcb while in err-mode, that'll tell you at which end the error is located

I don't get the point Jacob

 

[gyraf]

If error is on the pcb, needle will unstick when pcb is disconnected?

 

[frenkonio]

If error is on the pcb, needle will unstick when pcb is disconnected?

Got it! Ok, I will see if the tiny small pcb behind (and inside) the meter can be detached easily asap and let you know... but your guess is nice. I'll try. Thanks!