Meter Repairs

[Hyounce]

Can anyone recommend a shop for meter repairs. I have a Tuner Level meter that's dead in my Sony ST-5000FW

 

[singa]

Meters rarely fail,check the connections or maybe just tap the top of the meter the needle may be stuck. Regards.

 

[Hyounce]

I'm going to tackle the problem this morning. Connections are all solid and the needle appears to be driven to full scale deflection. When you physically move the needle it pops back over to full scale. You can adjust the pot that controls the sensitivity of the meter through it's full range without effect on the meter. It appears that the coil spring is unable to return the needle to zero position when the input signal is lowered or power disconnected from the meter entirely. Bye the way, is the level meter typically a volt meter or an ammeter? Haven't really thought about that aspect and have been treating it as a voltmeter all along. Thoughts?

 

[singa]

Hi, Oh dear this is a bad one, I mean it seems that the needle or pivot is not
sitting in it's usual place.You may need a maginfying glass to check it.Or
the coil spring is twisted but if the electrical connection is still intact(to the coil spring) then it may just work if you put it back into the "well" of the shaft.Use tweezers they help in this situation.

It's delicate so be gentle with movement there's not much slack.but if the connection is broken I don't think it's worth repairing.Level meters don't
cost much.Of course you should find one that fits.

Meters are specified by the current it takes to show full scale.So naturally
it will take a certain voltage to swing so much current.So with the corresponding voltage or current in can be calibrated to show one or the
other.Maybe you should try the sony agent if there are spares?
Regards.

 

[Hyounce]

No spares. The tuner is no longer supported, and parts are no longer available, even at their repair center. I took the front of the meter off and verified the coil spring was still in tact and connected. I began dissembling the front bearing mounting bracket and when I loosened it slightly the meter sprang into action. Apparently, the bearing had dried out and was preventing the meter needle from moving freely.
I had no way of calibrating it, so I zeroed the needle with no signal, and tuned in the strongest station I was receiving and adjusted the meter to a point just short of full scale. Probably not correct, but it will give me a relative signal strength as I tune across the dial. Probably not the best procedure, but I managed to stumble through the problem. Anyway, thanks for all your advice.
Now it's on to tuning the power supply. I'm seeing the B+ coming in about 6 volts high (30.2 instead of 24.0) and the pot that is suppose to adjust the output voltage has no effect at all. If you still have the schematic of the supply, the adjustment is made through R601. The tuner works just fine, but it bugs me to not be able to bring it into spec.

Henry

 

[singa]

Hi, Congratulations on the meter repair ,you have described something "new"
so this one goes into the repair notes.

The pot R601 you mention may be bad try a substitution to get it to 24V.
Ps or is there a 7824 somewhere?
Regards.

 

[Hyounce]

I'm going to get back to the Sony in the next day or so. Like I mentioned, the tuner works great, but I don't want to operate it continuously at the higher voltage. It also bugs me that the voltage adjustment feature of the circuit doesn't work as it should. It sure would be nice if the original transistors were still available. with all the "substitutions", I'm not sure what I should expect.
Would be nice if there were a 7824 in the scheme of things, but I'm afraid that's not the case.
Henry

 

[gain wire]

Hi Henry!

I had to go to your profile in order to find the schematic link posted in the original thread.
anyway, this is long before the 78-xx days! I am just now looking at the schematic..

by the way running it at roughly 20% higher voltage is not too good in my opinion...