Bench Setup

[memoryman]

What equipment do I need for a safe repair bench setup?

[phatt]

Hi memoryman, Welcome to the party. :tu:

You should get some really good advice when the techs finish work.
Meantime here's a few of my Do Nots.

Number one rule is don't touch anything you can't outrun. :cheesy:
Don't work Alone.
Don't wear Jewelry
Don't work in bare feet
Don't use cheap low grade DMM's if you are working on high voltage gear
Don't assume something is off,, always check.

I work on a wooden bench.
I stand on a 20mm thick rubber mat

As to equipment just get the basics first,,
A good DMM and meantime build a light bulb limiter
they are cheap and simple to make and can save
a lot of heartache try to fault find.
http://www.ssguitar.com/index.php?topic=2093.0
Phil.

[memoryman]

Do I need an Isotap or Variac?

[Enzo]

Do I need a bread knife and a grapefruit knife in my kitchen?    Only if I am cutting bread and grapefruit.

Those are great things for a complete shop to have, but it all depends on what you are doing.   Those tools will not be of any use if you are winding pickups or building speaker cabinets.

Iso transformers are a must for working on SMPS, but I rarely use one otherwise.   I find the variac mainly of use working on solid state stuff rather than tube stuff.   Neither will be much help building overdrive pedals.

[Roly]

I have got by for many years now without a Variac, but I couldn't survive without a good dummy load.  @Phatt has already mentioned a limiting lamp.  You can get by without one on valve/tube amps, but it is essential for working on solid-state amps (unless you enjoy repeatedly replacing brand new semiconductors).  While they overlap a Variac and a limiting lamp serve rather different needs.

A signal generator and test signal sources such as a cassette or MP3 player.  Doesn't have to be fancy or super low distortion but it should have at least a reasonably clean sine output and be able to cover the audio range, 10Hz to 10kHz.

At least one good multimeter rated for the highest voltage you expect to encounter.  Both analogue and digital meters have their strengths and weaknesses, so I have several of each.

An oscilloscope.  Again it doesn't have to be fancy but even the most basic CRO is better than no CRO at all.

Working on synths and guitars I have found a frequency counter very useful for precise tuning, and it also removes the need for a signal generator with an accurately calibrated dial.

A Megger or similar high voltage insulation tester and high range megohmmeter.

A neon screwdriver to detect high voltages has been a life saver when a "dead" mains circuit or "discharged" high voltage caps in valve/tube amps turned out not to be.

I also have an LCR bridge for testing capacitors and inductors.

Bench power supplies of voltage range and current capacity depending on your needs, what you get in to.  I have several, 5V, 12V, +/-15V, 6.3 and 12.6VAC, and switchable high voltage up to 400 volts.

A bench loudspeaker, or two if you work on stereos.

And hand tools, lots of them.  A good soldering iron and stand (I have several of different powers), and a solder sucker, the biggest you can find.  Screwdrivers of every type and size, ditto pliers, and in particular good sidecutters.  I also have several suture clamps that get a lot of use.  Lenses and magnifiers for the increasingly microscopic world inside electronic gear.  Lots of dusting brushes, a "dustbuster", and big vac.  A torque-limited power driver and multi-bit sets for when you have to take out or replace lots of screws (synths, speaker boxes, etc).  Adjustable spanners small, medium and large, and socket sets and drivers.  A range of clamps, spring and screw, from tiny to large.  A bench vyce or three of different sizes.  Hacksaw small and large (particularly for cutting new pot shafts to length, but you should have a specific dirty area for metalwork well away from the electronics bench and speakers).

Writing implements, pencils, pens, felt tip pens in colours and sizes.

A bench notebook, and these days a digital camera with good macro capability for "records shots".

A bench calculator or slide rule (which never has a flat battery).

Leads; screened signal leads that allow you to adapt any sort of connector to any other sort, unscreened speaker leads both long and short, clip leads for informal connections.

Power boards (with inbuilt overload protection) so you have somewhere to plug everything in, and an Earth Leakage Breaker if there isn't one on the main switchboard.  (and note that if you use an isolation transformer you defeat the operation of an ELB.)

And by no means least, good lights, both general and adjustable so you can really see what is going on.

A rubbish bin and storage boxes to keep stock components and hardware in order and easy to find.

I also have several computers, for office work such as job sheets and records keeping, design work such as circuit simulation, PCB layout, circuit drafting, internet access to find circuits and component datasheets (giving advice and asking for help), and an old clunker for experimental work in the workshop which would be no loss should I happen to accidentally apply 400 volts to one of its ports.

Thermocouple (contact) and non-contact thermometers, sundry weights and scales, micrometer, vernier calipers.

etc., (I'm sure others will chime in with what I've forgotten).

[joecool85]

I have got by for many years now without a Variac, but I couldn't survive without a good dummy load.  @Phatt has already mentioned a limiting lamp.  You can get by without one on valve/tube amps, but it is essential for working on solid-state amps (unless you enjoy repeatedly replacing brand new semiconductors).  While they overlap a Variac and a limiting lamp serve rather different needs.

A signal generator and test signal sources such as a cassette or MP3 player.  Doesn't have to be fancy or super low distortion but it should have at least a reasonably clean sine output and be able to cover the audio range, 10Hz to 10kHz.

At least one good multimeter rated for the highest voltage you expect to encounter.  Both analogue and digital meters have their strengths and weaknesses, so I have several of each.

An oscilloscope.  Again it doesn't have to be fancy but even the most basic CRO is better than no CRO at all.

Working on synths and guitars I have found a frequency counter very useful for precise tuning, and it also removes the need for a signal generator with an accurately calibrated dial.

A Megger or similar high voltage insulation tester and high range megohmmeter.

A neon screwdriver to detect high voltages has been a life saver when a "dead" mains circuit or "discharged" high voltage caps in valve/tube amps turned out not to be.

I also have an LCR bridge for testing capacitors and inductors.

Bench power supplies of voltage range and current capacity depending on your needs, what you get in to.  I have several, 5V, 12V, +/-15V, 6.3 and 12.6VAC, and switchable high voltage up to 400 volts.

A bench loudspeaker, or two if you work on stereos.

And hand tools, lots of them.  A good soldering iron and stand (I have several of different powers), and a solder sucker, the biggest you can find.  Screwdrivers of every type and size, ditto pliers, and in particular good sidecutters.  I also have several suture clamps that get a lot of use.  Lenses and magnifiers for the increasingly microscopic world inside electronic gear.  Lots of dusting brushes, a "dustbuster", and big vac.  A torque-limited power driver and multi-bit sets for when you have to take out or replace lots of screws (synths, speaker boxes, etc).  Adjustable spanners small, medium and large, and socket sets and drivers.  A range of clamps, spring and screw, from tiny to large.  A bench vyce or three of different sizes.  Hacksaw small and large (particularly for cutting new pot shafts to length, but you should have a specific dirty area for metalwork well away from the electronics bench and speakers).

Writing implements, pencils, pens, felt tip pens in colours and sizes.

A bench notebook, and these days a digital camera with good macro capability for "records shots".

A bench calculator or slide rule (which never has a flat battery).

Leads; screened signal leads that allow you to adapt any sort of connector to any other sort, unscreened speaker leads both long and short, clip leads for informal connections.

Power boards (with inbuilt overload protection) so you have somewhere to plug everything in, and an Earth Leakage Breaker if there isn't one on the main switchboard.  (and note that if you use an isolation transformer you defeat the operation of an ELB.)

And by no means least, good lights, both general and adjustable so you can really see what is going on.

A rubbish bin and storage boxes to keep stock components and hardware in order and easy to find.

I also have several computers, for office work such as job sheets and records keeping, design work such as circuit simulation, PCB layout, circuit drafting, internet access to find circuits and component datasheets (giving advice and asking for help), and an old clunker for experimental work in the workshop which would be no loss should I happen to accidentally apply 400 volts to one of its ports.

Thermocouple (contact) and non-contact thermometers, sundry weights and scales, micrometer, vernier calipers.

etc., (I'm sure others will chime in with what I've forgotten).

Great post, this should be a sticky - would you be ok with that?

[Roly]

Sure - you like it, it's yours (and there's a lot more where that came from  :lmao: ).

[Enzo]

The variac is only half a tool, the tool is a variac AND current meter.    I watch the current as I advance the variac from zero.   If the current starts to ramp up, I back off.   That is the same current that would be lighting the limiter bulb, except with the variac I can find out there is a problem while only applying 10 volts to the circuit.

[memoryman]

I have had my eye on VIZ WP-27A Isolation Transformer which seems like a combo isolation transformer and a variac. Being a newbie I was thinking it would be benificial to have this between myself and the power supply(Wall).

[Enzo]

No, that is not at all a variac.   That has a voltage adjustment, yes, but you cannot start at zero and inch your way up.

[Roly]

Buried in my comments above I said this;

Earth Leakage Breaker if there isn't one on the main switchboard.  (and note that if you use an isolation transformer you defeat the operation of an ELB.)

Before ELB's an isolation transformer was a way of getting a local bench mains supply that wasn't grounded on one side.  Because it was floating it meant that you weren't automatically connected to one side of the supply to begin with, and that you therefore had to touch both sides rather than just one to get a shock.

Earth Leakage Breakers (also variously known as Safety Switches, Core Balance Relays, etc) changed that picture dramatically, and provide far better protection than an isolation transformer.  These work by detecting any leakage from the active side of the mains to ground, but this has two vitally important implications;

- an ELB will only protect you if you are grounded,

- an isolation transformer will defeat ELB protection.

An isolation transformer is better than nothing, but an ELB is much better than an isolation transformer because if you do happen to get hooked between active and earth it will cut off the supply so fast it greatly reduces the chance of a cardiac ventricular fibrillation, the arrhythmia that kills.  You get hooked across the secondary of an isolation tranny and you will just cook.

If you are well grounded an ELB will even give you a measure of protection if you happen to touch both Active and Neutral because part of the current will flow back via the earth circuit.

@Phatt's advice about a wooden bench and rubber mat is subject to exactly the same reasoning and function as an isolation transformer; better than being grounded if you don't have an ELB, but potentially deadly if you do.

Because transformers and ELB's can fail, plugs and outlets can get miswired, etc, there are some simple rules you should always follow, particularly when working on mains wiring (and they have saved my life on several occasions);

- don't touch what you don't have to.

When you do have to;

- check "dead" wiring with a neon screwdriver; test the driver on an active, test the "dead' circuit, test the driver again.

- first touch with the back of your hand (so you don't reflexively grip a live conductor)

When working on amps;

- the very first thing you should always do is check the mains plug wiring is correct and secure, and particularly that the earth pin is actually connected to the chassis with a low range ohmmeter.  Make it a habit.

- don't just switch off at the outlet, unplug the power lead and put the plug up on the bench where you can see it.


These precautions, like most safety procedures, are a time wasting pest, but once in a while they will save your life.

Things don't always go according to plan, sometimes you unplug the wrong lead, or some idiot does something deadly.  I used to do installations of electronic press guards and die protectors that sometimes required work on the press control box.  It was my habit to remove the fuses, tag the fuse carriages, then take the fuses with me and put them in the lid of my toolbox.  One time I returned from lunch and before resuming work used my trusty neon screwdriver just to confirm that the control wiring was still dead - and it wasn't.  Some dickhead wanted to do a personal job on the press I was working on (with the guts of the control box hanging out) and had pinched some fuses from a different circuit and livened the press up, then walked off and left it that way, just waiting to kill me when I got back.

I certainly don't advise it, but I'm living proof that you can work on live switchboards safely, provided you take sufficient precautions - the first time you decide it's too much trouble and cut corners may be the last time you do anything.  And there are worse things than getting killed - search YouTube for "arc flash".

Always treat the power mains with ultimate respect - the amount of current that can kill you doesn't even qualify as "leakage".

Charged capacitors in power supplies are also a hazard.  Mostly they are discharged during power down, but not always, and particularly if the amp has a fault (and why else is it on the bench?).

The high voltage line in a valve/tube amp is unlikely to be lethal, but it can still give you a very painful bite and burn, cause you to drop and damage the amp, etc., so always make sure with your voltmeter that the supply rails are discharged, and if not, discharge them before work.

Discharging them by simply shorting is not a good practice because it is unkind to the capacitors and often not fully effective, and in the case of large solid state amps can produce an explosive spray of molten metal that was the blade of your favorite screwdriver.  A power resistor with a couple of soldered clip leads clipped across the supply before you commence work underchassis is the right way and a good insurance.

And lastly, "it's the volts that jolts, but the mills that kills".  The amount of current that can kill is only milliamps, not enough to light up a torch (flashlight) globe, and the worst situation is between your hands so the current flows across your chest cavity.  So when probing live circuits keep one hand out of it, in your back pocket as some do, and rest your wrist on the grounded chassis so that if you do happen to contact something live the current will be shunted to ground at your wrist, not pass through the rest of your body.

Follow these rules faithfully and you will have many happy and interesting years tinkering on all sorts of hideously dangerous gear such as 100 amp three-phase circuits with wires as thick as your finger, or X-ray machine power supplies (100kV @ 100mA), and still live to be an old curmudgeon like me.      :dbtu:

[Enzo]

Roly, if I read you well, it seems you are equating the iso with the sort of protection a ELB provides.  Here in the USA we call them ground fault interrupters or something like that - GFI.

But in my shop the entire point of an iso is to get the circuit reference away from earth.   All the ELBs on earth will not let me connect my scope ground to the -170v of an SMPS.   That is what the iso is for.

[Roly]

All of my instrumentation, my CRO in particular, have floating grounds through fully isolated supplies internally.  The supply is built on metal which is mains grounded, but the secondary side supply isn't grounded, left floating.  Now I'll admit that this slightly increases tech's risk from a winding-to-winding short, but the trannies available here in Australia are made in China but to full AStandard, and it's so rare with modern small transformers, and taken in connection to ground at one point in actual use, the amp under test mains ground normally, the increased risk is minimal.  But I'm talking side-by-side bobbin wound, not paper-in-layers overwound.

I have/had CRO's in my collection that have had ground lift links between two terminals on the front panel, etc.

[joecool85]

Sure - you like it, it's yours (and there's a lot more where that came from  :lmao: ).

I changed my mind, this whole thread is great, so I'm just going to sticky this!

[Jack1962]

Here are the basic items you need to have on your test bench:
1. a simple screwdriver set
2. needle nose pliers
3. wire cutters
4. good lighting(probably should be #1)
5. Soldering Iron
6. DMM (the quality of this item is up to you)

these are the basic tools needed for a complete test bench you need a great deal more tools and money to buy them with , but this is all you need to get started.  :dbtu: