Sholud I get more diagnostic tools?

[mtlbasslad]

Hi all - well the title says it all - should I?

After my last adventure into a Marshall 6100 I was frightened by all the boards, IC's, ribbon cables etc... a long way from point to point Fenders...

I thought maybe a signal generator would remove the need to borrow my wife's Strat & keep strumming while I tried to figure out what was going on in the amp - there are cheap ones on Amazon under $100 - so I ordered one

Now of course I'm looking at cheap ($250) digital oscilliscopes - could a noob like me really use these tools?

The only really quality tool I have is my new Fluke multimeter - and you guys

Your opinions welcomed

Cheers, Lorne

PS - the Marshall 6100 will be onstage tonight - let's hope no 'magic smoke' appears

[Jazz P Bass]

If your goal is to keep repairing amplifiers then a signal generator is a must.

A scope is a plus as you can actually see the waveform.

I would add a Kill-A-Watt meter to the list.

[g1]

I think you mentioned elsewhere people starting to bring you stuff to fix. Get a scope, you'll never regret it.

[Enzo]

You don't need a digital scope, though they work too. Any old analog scope will be good enough.

I use a signal generator for certain things, but for general work, I just run a cable from a CD player and use the music for a test signal.

[olddawg]

Or get a signal generator app for your phone...

[Tom Phillips]

In order of importance I would choose the following to have as a minimum:
1) DVM (which you already have)
2) Signal generator
3a) Scope
3b) Dummy load
4) Variable AC supply ("Variac")
Those are the basics and there are many advanced instruments that are nice to have such as spectrum analyzers,tube testers, transistor testers and more. However, the best is to develop a good understanding of how circuits operate and practical troubleshooting skills coupled with a good thinking to filter out the BS mojo that floats thru the internet and the books published by self appointed gurus.
R,
Tom

[Mick Bailey]

For a test signal I mainly use a single-transistor 1khz sine oscillator I built in the 70s and is still going strong. It just has an output level control and on-off switch. I have that to hand all the time. For bass and PA amps I have a simple hand-held signal generator.

[bob p]

In order of importance I would choose the following to have as a minimum:
1) DVM (which you already have)
2) Signal generator
3a) Scope
3b) Dummy load
4) Variable AC supply ("Variac")
Those are the basics and there are many advanced instruments that are nice to have such as spectrum analyzers,tube testers, transistor testers and more. However, the best is to develop a good understanding of how circuits operate and practical troubleshooting skills coupled with a good thinking to filter out the BS mojo that floats thru the internet and the books published by self appointed gurus.
R,
Tom

5) Light bulb limiter.
6) Isolation transformer.

[Brad1]

Relatively cheap and useful items:

Bleeder resistor with rubber-covered alligator-clip leads to drain capacitors on unplugged units.

Chopsticks, to poke around inside a live chassis flexing wires, etc., tapping on tubes, and eating Kung Pao chicken while you ponder the problem.

Advil, for when what you pondered while eating your Kung Pao doesn't work.

Contact cleaner, like De-Oxit.

Assuming you already have a good soldering rig?

A tube tester might come in handy to get a general idea about tube health, and strength?

Brad1

[bob p]

^ A good soldering station, or a reworking station, is going to be an essential piece of gear if you plan on working on PCB equipment. If you plan on working only on turret boards and eyelet boards then you can get by with a cheap low-watt soldering iron, a heavy-duty soldering iron and a soldering gun.

[Enzo]

Agree with all the above.

I think technique is more important than having a ton of gear. In my pro shop, the vast majority of work is done with meter in hand. My scope is always running so I can reach for it. Learn what you are looking for in the amp. I can check ripple with my meter, with my scope, with a signal tracer. The important thing there is knowing what ripple is and where it comes from.

[jbltwin1]

Check ebay for some of this stuff. I bought a LIKE NEW sig gen for 20.00 to replace my 50 year old one that was as big as a car. My scope is an old school scope from the 60's. Works just fine for audio unless you need dual trace. A good audio probe is handy too, if you either have a spare amp or an old audio tracer amp like mine. THAT is also probably 50 years old that is on my bench. A good ESR meter is great for finding crap caps. I have an old Eico electrolytic cap checker that ALSO still works like a charm and it's even older. Maybe 50's? Mike.

[Mick Bailey]

I think technique is more important than having a ton of gear.

Technique and experience are the keys to effective troubleshooting. Reminds me of the phrase "All the gear, no idea". No amount of test gear makes up for poor technique. It's worthwhile studying repair techniques - how to track down a fault quickly and effectively by observation and understanding. There's a certain feeling you get when you identify a defective part, replace it and fix a problem. There's no satisfaction whatsoever in replacing good parts and making no difference, or introducing new problems.

Simple techniques can overcome lack of equipment. I remember Enzo describing using a DMM and diode to see if half a waveform was missing - the guy didn't have a scope. A friend had a problem with his fuel-injected bike. He started looking at expensive diagnostic equipment. I used a DMM plus grain-of-wheat lamp soldered to some clip leads and sorted his problem out in 15 minutes.

There are some good references to technique - Jack Darr's books, the Tektronix scope troubleshooting handbook etc. It doesn't particularly matter which field of electronics - its the techniques you're looking for.

[mtlbasslad]

Thanks for all your replies - good advice as always.

Here is what I had on hand before asking the question:

Fluke 115 (measures capacitance & is auto-ranging, YAY)
Weller WES51 soldering station (gift from child, more YAY) along with solder pump, de-soldering braid
Light bulb limiter I built last year on advice from y'all
Dummy load is an 8 ohm speaker...
Helping hands gadget, heat sink paste, heatshrink, hooks & pics assortment, Deoxit, freeze spray...
And chopsticks !

Now I have a Kuman FY2202SP signal generator & a Hantek DSO5072P oscilliscope on the way... still looking at a 3 amp variac...

And the best advice I got from you all is of course to try & know what i'm doing. To that end I have asked my child to loan me the book I bought him when he was 12 - and I will read it.

I like to think I have good analytical skills coming from 15 years of programming mainframes - as in follow the signal path.
And keep one hand in my pocket LOL

No doubt I'll be needing your collective help when the new toys arrive, wish me luck!

Thanks, Lorne

P.S. Next project is a 50's Silvertone 1432 rescued from an abandoned building - got it working except for the tremolo, clusterf*%k of caps & resistors around the 6AU6 tube...

OOPS, forgot the venerable Knight 600 tube tester, for what it's worth...

[mtlbasslad]

Postscript to this thread...

Would a 500VA (.5KVA) Variac be big enough for my needs here? It's $90CDN with free delivery - everything else delivery is as much as the cost... ??