Multimeter Blues...?

[argon]

I'm examining the electronics of my Rickenbacker guitars, and man o' man, most pots are WAY out of spec. But I've had a difficult time reading pot resistances and capacitor values. Finally, after much testing, I've pretty much concluded that my problem getting readings from caps (smaller caps, look more like large resistors; 0.047 and 0.0047 uF) is that the leads are insulated (as they should be) but it was a little difficult exposing bare areas of the leads to touch with probes; had to push back the insulation a little at each end of the cap. I finally aggressively pushed back the insulation to expose at least 2 mm of bare lead, and then I got seemingly consistently good readings rather than erratic or no readings at all. I figured that there must be some sort of thin coating (epoxy?) on the leads immediately adjacent to the cap. I don't know what to say about reading pot/ohm values (these Rick pots are weird; I may post a few results later).... which makes me think...

...that these "auto range" multimeters aren't the cat's meow, after all. I have a couple of cheap CEN-TECH meters that I got for free from purchases as Harbor Freight a few years ago; limited in capability, but OK (model 98025), at least for working on my cars. A couple of years ago I searched for a better meter that included cap testing and audible continuity. Coincidentally, I ended up buying another CEN-TECH (98674) because it seemed to get good reviews across the 'net (in spite of it being an ugly dark green monolith).

So, the more I use this auto ranging meter, the more inclined I am to think that the auto ranging feature could be the source of some frustration in getting consistent and accurate readings. Sometimes I think it's the contact of the probe tips not penetrating a layer of oxidation; I'm not sure, but the meter is not as responsive as I want. I really need to be sure that the readings I'm getting are truly consistent and accurate. I'm beginning to think that this auto range feature may contribute to inaccuracy, as it goes through its diagnostic value ranging routine each time I test; a short but annoying delay, with possible inaccuracy on top of that. I'm at the point where I can't trust my meter because of this.

What is your opinion of auto ranging meters? If you can appreciate the annoying quirks of auto ranging (or maybe it's just my cheap/$65 meter), the perhaps you can suggest a good non-auto ranging digital meter. I think I need a good reliable, bulletproof meter, with wide-ranging diagnostic sensitivities that include audible continuity testing and capacitor testing. This time I won't be afraid to spend a little more cash to get more reliability. It's OK to have to think a little and turn a dial....

 

[John Canon]

Good job! Much of electronics troubleshooting is probing and good equipment gets you there. After many years and many multimeters I finally bought a Fluke digital multimeter DMM. The Fluke 110 series has several options. Also you can choose the range for each switch position.
My 117 model (called the Electrician model) offers a capacitance setting, plus ohms, amps, hertz, millivolts, min/max and beep. There are probe tips available with a little retractable hook that can grab the lead.

 

[Harald Kapp]

The problem may be specific to your multimeter, it definitely isn't specific for autoranging.
Or it may be due to your way of testing: When testing components, always remove them from the circuit, otherwise other elements in the circuit can have a random influence on your measurements. Often it suffices to remove at least one of the legs you use for testing from the circuit.
There are ways of testing components in-circuit, but these require sophisticated test equipment which is able to shield the measurement from the influence of other components.

 

[argon]

Thanks for the recommendation, John. However, I fear I had a much too simplistic view of component measurements, now having read Harald's information: Thanks, Harald. You can't always believe what you see/hear on YouTube...

This deep dive I took into measuring all components on my guitar started simply by wanting to find out why the bass (neck) pickup tone control did not change the guitar's sound whatsoever at either pot adjustment extreme; all "bass" and no treble increase change. The pot measures 184 k ohms across the outside terminals. I checked the center terminal and an outside one as I measured resistance at: full counter-clockwise (near-zero), 1/4 (9 k ohms), 1/2 (42 k ohms), and 3/4 (108 k ohms) from that starting position, and then full clockwise (184 k ohms). The spec for the pots is 360 k ohms; you can see that my measured value is about 1/2 of that 360-k ohm spec. (two tone controls, bass/neck pickup and the treble/bridge pickup).

I expected the pot to be dead or severely defective, but it seemed to respond appropriately, yielding incremental readouts typical of an audio/log pot. Here's a link to the schematic.

19512.pdf (rickenbacker.com)

This specific guitar (model Rose Morris 1996 [very limited series, not listed on schematic], a British import version of the 325) has the treble boost cap installed (no longer installed now but was installed to copy the 1960s design; 0.0047 uF, between the switch and the treble volume pot; on the schematic, the connection is shown simply as a wired connection, or as Rickenbacker now calls it (re: vs. the cap), a shunt. That small cap greatly adds the "jangle" sound of a Rick; I also do not notice much ranging change from the treble/neck control. There "seems" to be something deficient about this wiring design; could be my aging ears, however. But tone control should be effective enough to render an easily noticeable (not subtle) sonic change, it seems to me.

I found this, but it's way over my head. Some of you may find it interesting enough to read through:

The Science of Electric Guitars and Guitar Electronics (guitarscience.net)

I have a different Rick, and its bass/neck tone extreme adjustment is only Barely noticeable. It doesn't seem right. Well, thoughts appreciated.

 

[kellys_eye]

Note that all those controls have one side grounded. Often this ground may include a connection to the body of the variable control (metal casing of the potentiometer). In any case you need to confirm that the ground is attached and continuous throughout the wiring as 'lifting' the ground wired side of any of those controls will render that control 'ineffective'.

The value of the potentiometers does, of course, have an effect but they are notoriously out of range from whatever they were marked - in many case up to +/-50% - so don't be too fixated on the actual value, just concentrate on getting it to 'do something' for now.

 

[argon]

So, I'm laying in bed this morning, just waking up, and I have this profound revelation; stated as a question: Why do my Ricks sound so dull? Why are my Ricks so functionally unresponsive? They all can't be defective!

PART I: Wrestling with the meter

Well, I finally thought that maybe the guitar-amp cord I was using was defective. I checked the resistance of three different guitar-amp cords: all vary but have less than 3.0 ohms resistance each, depending on length of the respective cord. I had a difficult time getting a consistent reading using my better DMM; slow rise in reading, then up & down. The slightest movement of a probe and the meter starts again with variable results. Why is that? It seems like the probes are not very conductive. I could have put allegator clip adaptors on the probes and clamped the cord plug, but I was going through three of them and comparing results with two different meters. Is this common, to have your meter readouts bouncing around? I can't be sure of the result unless I check with a second meter; that's no good.

PART II: I'm only human (although, sometimes a human knucklehead)

Since the cords seemed to be OK, I hauled out another small amp, plugged in a troublesome Rick, and there it was -- the missing tone range! I ran through all the pot adjustments and they all were responsive. What a relief. I'm not thrilled that my VOX amp is not working (I had also noticed a drop in volume output), but I'm happy that my guitars are working OK. Of course, I should have checked these other things first....

This particular VOX combo amp (Pathfinder 15R) is solid state. I don't think I'm going to dive into this and try to repair it; probably has a circuit board. Maybe someday. (I bought it used, but it seemed to work fine over the last couple of years.)

Thanks everyone who helped me put, providing suggestions, etc. I really appreciate it. You can't get this high-tech advice from a guitar forum.

PS - I've been wanting to re-learn Morse Code (from my Boy Scout & Wig-Wag flag days) and use it with a telegraph key; my next little electronics project is putting a small key/module assembly together. I was surprised (here, in 2022) that I could not find a smart telegraph key that I could plug into my PC and, with accompanying software, practice all sorts of sending & receiving scenarios. I ran across web sites that sort of do this stuff, but they didn't seem like something I could use; I really wanted a stand-alone system. The little kit I bought has a small digital screen that reports the letters I key out. Well, it should be fun putting it together; I imagine I'll re-learn the Code.