Repairing switch mode power supplies

[Zipslack]

quick suggestion

One thing you might want to consider is building a couple of smps to help understand them better. Something like the nixie supply is simple and useful for a starter project for experimentation. Radio Shack used to carry a small book on building your own power supplies that is pretty good for learning about smps.

[Jazz P Bass]

Here is a link to an SMPS explainer file.
http://music-electronics-forum.com/t23974/
What really is bad with SMPS is when the surface mount components or main drivers go up in smoke.
There is usually severe damage done to the actual PCB.
Which puts a damper on any hope of actually repairing the supply.

[MarkusBass]

What really is bad with SMPS is when the surface mount components or main drivers go up in smoke. There is usually severe damage done to the actual PCB.

I haven't noticed that this is a problem. In all cases that I had there were 6-10 components to be replaced and 1-2 tracks to be fixed. With SMT components there is a bigger problem if you don't know the value of the component (and you have no access to the schematic).

Mark

[MarkusBass]

ANYONE KNOW ANY TECHS INTERESTED IN LIVING IN COLORFUL COLORADO & WORKING IN THIS FIELD? ;-] glen

Glen,

You haven't mention what would be the main task for this person. The topic is about fixing SMPS but you rather mention keyboards. Which one is it? For me amps, SMPS and talking to musicians (I'm also a musician) are OK, but keyboards are not OK . It's too much digital technology. I'm not affraid of it but I don't have much experience in this field.

Mark

[km6xz]

A shop owner has a double edge sword cutting at him, an ever diminishing number of qualified potential employees and the customers perception that repairs should be cheaper because equipment is getting cheaper every day.
To attract a tech worth having, who can earn their keep requires quite a commitment in salary and benefits that is usually not in the universe of pro audio repair.
The only techs with the chops needed to do the work on a professional level are older adults who are established, often with a family and middle class expectations, moving allowance, etc. It takes only a few years for an EE to be effective but it takes decades for a tech to be at the pro level unless they are going to do assembly line sort of work on one type of gear. I've tried a couple of models in developing a tech staff. There is no simple answer but for units that are in high volume a depot type work flow worked well for us, and the general stuff worked on a combination of skilled tech supervising a small team of lesser skilled techs and narrowly designated work load for those who were effective in one or two things. For example I had one tech who had worked on a tube guitar amp every day of his life for 40 years and was very meticulous and methodical. He only got tube guitar amps to work on and mostly from VIP clients. But the rest of the techs had to have their work conditions adjusted to work around limitations in diagnostic skills or experience. My best keyboard tech had no prior experience but had an extensive high level recording career. I trained him from scratch and it worked out to be a very good investment.
Unfortunately, for the lack of workers who can be productive, the business has to be very flexible, that is not going to change, only get worse. The major employers of techs in the past such as HP and Motorola funded many community college electronics programs in the 70-80s but gave up trying to find effective techs and grads from those programs, it required too many compromises. They redesigned some gear, changed service policies, and stopped expecting tech competency. Things became more black box swapping and major assembly exchanging.
The problem with any field that has a strong hobby aspect like music gear, has a strong resistance to professional level charges, most shops have to keep an hourly rate to below what a qualified tech would deserve in any industry that was not hobby based. After all, the client assumes someone will do it for free because it IS only a hobby. Just an example, medical equipment techs generally do not have as wide a range of technologies to master yet because it is not one dominated by hobby oriented valuation, earn 2-5 times as much as audio techs.
This thread about switching supplies is a good example of niches that lower level techs can be used for, depot style volume exchange repair for popular power supply modules. A rebuilt supply exchanged for $40 for example would generate a lot of exchange business if the work flow was focused on such a narrow specialty.
Remember back in the day, TV tuner repair was tricky for neighborhood shops so specialty shops sprang up to offer them exchanged for less than a general repair shop could do them. For about 2 decades 2-3 companies would do them in volume for $10 exchanged. But they had millions of potential repairs funneled to them, in pro audio there is so little concentration in any brand or model to gear up to high enough volumes to drop the prices to a great deal lower than a general repair shop could do them. The main advantage would be speed of exchanges from inventory.

[Jazz P Bass]

I would love to see manufacturers use a module for the SMPS.
But, Noooo.
To save cost, the amp is one board.
What a bitch, when the supply goes up in flames.

[Mars Amp Repair]

Well I couldn't have put it any better.

Yes it is very difficult to find anyone still in this industry & you are completely correct that much of what we do relates greatly to years of experience & not just schooling, and as you mentioned we do get paid wayyyy less than our counterparts say in the medical field who now are swapping assemblies.

I tell my guys the wages made in this industry is just what this repair industry dictates. You can only charge so much. So as a tech you have to hone your skills...not just technical skills but have the ability to make quick definitive decisions on the item in front of you.

I used to set an alarm clock for 45min when working on VCR's. If I hadn't gotten any closer to a solution to the issue in that time & couldn't see that I was close to a breakthrough, I'd get off of it & onto something else that I might be able to get done that day (that's very settling on your mind knowing you at least made some money that day). If I thought another 15min would get me somewhere, I'd hit the snooze button and push on.

It took great discipline to obey my own rules and in the long run I became a very productive tech. The other piece of it is learning the value of 'the fresh outlook'. Anyone who has been a tech for any amount of time knows that the next day after struggling with a problem, you often would walk right to it in like 15minutes.

Frankly, in the 80's I was making much more money when I was repairing vcr's & camcorders in the '80s comparative to what I make now running my own business. Sad, but it's just the way it is. Ya gotta eat.

So again if there's anyone who knows solid state power amps, keyboards & such, we probably have a spot for you. ...Moving allowance? Puhlease! You just gotta love Denver...all that skiing & hiking, 4 wheelin'...yeah! ;-] glen

[rf7]

I'm going back to the original topic. If all of your test gear is ground lifted, can you safely work on a SMPS without an Iso-transformer?

[Enzo]

Think about it. If the control circuit on the primary side is referenced to the -170v rail, you would want to "ground" your scope to that rail. The 12v the IC runs on will then work between -170 and -158. Now connecting the scope ground lead to that -170v rail will short it to earth ground if your scope is grounded. Bad.

SO let's now say you lift the scope ground. Now you can connect the scope probe ground clip to the -170v rail and it won't short it out. However, NOW your scope chasssis and probe shell are all sitting at -170V. I wouldn't be too interested in grabbing ahold of that. If I reach to turn the V gain up on the scope, I sure hope my finger doesn't brush the probe connector right below.

Use an iso.

[rf7]

OK, thanks Enzo!