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Carver TFM-15 VU Meters
Carver TFM-15 VU Meters
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Old 1st December 2020, 12:07 AM   #1
AlexRivera is offline AlexRivera  United States
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Default Carver TFM-15 VU Meters

Hello Folks,

I'm bringing back to life a little Carver TFM-15 and so far so good, the amplifier section is all functional now but I'd like to make the VU Meters work then install some good looking LEDs on them, the problem I'm having is that, since I don't have any knowledge about VU Meters I don't really know what to be looking at.

In the Carver site I found a couple of threads where they talk about similar issues where a couple of 2.2Kohm 2W resistors where getting hot and they had to change the TA7318P IC and voila!

In my case I have already tried that and nothing, same thing, I have checked the voltage coming from the power supply and it matches to what's in the Service Manual, I have removed and measured every component in the board and they are all good, so I don't know what else to look at.

Again, I don't know how VU meters are supposed to work, all I have done is momentarily apply some DC voltage and they move, then apply same voltage with opposite polarity and they move back so I'm assuming they are OK?

I have measured their internal resistance and one is 260 ohms and the other is 270 ohms.

I notice that when I turn the Amplifier on and apply an input signal the needles move just a tiny bit but over time as I increase the input signal amplitude they keep going higher in the scale and never come back down to 0, so I have to manually return them back and start all over again, they will again creep up little by little until they reach the top.

So with all that being said, can anybody share some experience?, what should I be looking at?, what to measure?

Thanks in Advance and Happy DIY!
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Old 1st December 2020, 02:20 AM   #2
OldDIY is offline OldDIY
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The indicators are deflected by a constant current of 50-100 μA (no more!). 10-15kom at 1.5v. The frame is suspended on a thread or on needles freely. It has a spiral return spring and stops.
Make the backlight outside the indicator using transparent plastic light guides.
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Old 1st December 2020, 03:45 AM   #3
Mayank is offline Mayank  United States
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I had a Carver TFM-15cb with non working VU meters. The 2.2K resistors had burnt the PCB and the TA7318P IC as well. IIRC I had replaced the VU meter driver board with an inexpensive one from the auction site, similar to:

DC 12V VU Meter Driver DB Audio Level Board Power Amplifier Module for TA7318P | eBay

You can also use this to verify your VU meters are working!

(No Affiliation).

Rgds
Mayank
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Old 1st December 2020, 02:12 PM   #4
AlexRivera is offline AlexRivera  United States
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Quote:
Originally Posted by Mayank View Post
I had replaced the VU meter driver board with an inexpensive one from the auction site
This is a good option to try but what else did you have to modify to make the new board work? It seems to work with different voltages, etc?

Thanks
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Old 1st December 2020, 02:41 PM   #5
AlexRivera is offline AlexRivera  United States
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Join Date: Jan 2017
Location: Texas
Quote:
Originally Posted by OldDIY View Post
The indicators are deflected by a constant current of 50-100 μA (no more!). 10-15kom at 1.5v. The frame is suspended on a thread or on needles freely. It has a spiral return spring and stops.
Make the backlight outside the indicator using transparent plastic light guides.
Thanks OldDIY, does this mean that the needles should be coming back to bottom by themselves, even disconnected?

If they are not is because they are damaged? Dirty?
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Old 1st December 2020, 03:22 PM   #6
OldDIY is offline OldDIY
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Should return. Free movement (without current). Obstacles to movement. Suspension, frame centering, frame geometry, debris in the magnetic gap is broken.
Амперметр — Википедия
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