Need experts help with old Tandy multimeter...

[77transam]

Hello guys (& gals), Newbie here! What I've got is an old Tandy (RadioShack) analog multimeter. This belonged to my father and has sentimental value, so that's why I'm trying to fix her. He said he was testing a circuit and it quit working, so I took the back off of it and this is what I've found. I'm also posting the owner's manual schematic. Does this look like it would be possible to fix? Are parts (capacitors) still available? Any recommendations/suggestions would be greatly appreciated!

(By the way, my electronics skills are fairly limited, but I can solder ! The problem I have is identifying the parts to replace them. Also, what's the best way to clean battery acid/corrosion from off terminals? Thanks, Dave

 

[GonzoEngineer]

First of all, it looks like the two resistors that are burnt are in the "OHM's" measuring part of the input circuit. Quite possibly, he had the meter set to the Ohms mode, and connected the probes to a voltage.

I would first replace the two resistors, and give it a try.

As far as cleaning corroded terminals, use a tooth brush and some baking soda and water first, to neutralize any acidity in the gunk. Dry it with a hair dryer, and clean the terminals with steel wool or a scouring pad.

Let us know if it works after replacing the two burnt resistors (9.5 ohms and 110K ohms.)

If it doesn't work, the next logical step is to check the diodes and meter movement.

 

[OLIVE2222]

Hi,

9.5 Ohms are hard to get, 3.3 ohms + 6.2 ohms in the E24 serie will be OK
110 K is a standard E24 value

better to go for 1 or 2% precision resistance.

Olivier

 

[davelectronic]

Hi there. you need to be aware the replacement resistors 3.3 + 6.2 ohms go in series, not parallel. Hope you get the meter fixed.

PS. 1 or 2% precision resistance is the resistors tolerance. More accurate the resistor.

 

[77transam]

Thanks for all the advice ! I'm going to try the suggestions asap and I'll post the results. Thank you guys again!