preventative maintenance on this Hot Rod Deluxe?

[BrianS]

Not long ago I had one of these USA made Fender Hot Rod Deluxes in the shop that ended up needing a new OT & PT, plus a bunch of other work like fixing cracked solder joints, etc...Also, the amp had already had it's "problem" resistors replaced.

Now last night I had a customer bring in his USA HRD to my shop.  No exact problem, but he did say he had taken it to 2 or 3 other techs with some issues with crackling/noise/cutting out.  One place said it's fine, another place replaced a tube and I think one of them found a cracked solder joint.  I'm not exactly sure if the problem was cured to the customer's satisfaction or not.

I told the customer I'd check some things out.  I found some discoloration around R78 & R79...the ones that usually burn up the traces around them...and a couple other "hot" components.  I also found a couple of solder joints that look partially cracked.  See pics:

possible cracked solder joints (both pics are of the same joints):



Discoloration around R78&79:



Now, having seen what happens inside these things when something goes wrong, I'm inclined to recommend some preventative maintenance to the customer:  replace R78 & 79 and raise them up off the PCB a ways; check entire PCB for cracked solder joints & repair as needed & clean all pots, jacks, switches and sockets.

Usually as techs we get gear in that is already broken.  What I have here an amp that might have an intermittent problem, but might not and seems to be showing signs of possible future failure.  To me, it makes sense to do some preventative maintenance, but is that overkill?

What do you techs in the business think?

[sluckey]

Preventive Maintenance makes a lot of sense in costly, critical systems such as the air traffic control system. I made a career doing PMs for FAA. I don't think it's necessary in consumer electronics and I think you would have a hard time selling the idea to a guitar picker.

[BrianS]

I certainly see your point.  But, I also do guitar repair and I know that if an acoustic guitarist uses a case humidifier in the winter, he may save himself a whole lot of money down the road on crack repairs.  Or if you fix a crack when it's small, it probably won't get bigger (more expensive repair).   Or if your jack is a little loose, you tighten it rather than wait until the connections break and then fix it.

I just found 4 of the 6 screws that hold the PC board down rattling around by the tube sockets.  The other two were about ready to come out as well.   

[Willabe]

You might be able to show the guy where the PCB is heating up and turning color (scorching) and explain to him sooner or later the PCB traces/pads will lift off the PCB. Then tell him what you think should be done (lift the R's up off the PCB) and what it will cost.

Touching up PCB cracked solder joints is common on amps again just show him if needed.

Touching them up and changing those R's shouldn't be much time wise/cost wise.


                Brad       

[eleventeen]

+1 on getting the R's elevated off the board. As far as I'm concerned, that's a design shortcoming; that degree of discoloration on the board. If it's possible, you may want to use 2 R's in series, same wattage rating, each one half the resistance.


As for the cracked solder joints, really, only you can tell, they do not look bad, but I am/we are looking at a pix. Are you talking about a circular failure/oxidation pattern in those...?


The problem with this kind of stuff is that it is hard to charge for it. From what I have seen of the serious weak points on these, if one of these was open on my bench, I would replace the ribbon connectors with separate individual stranded wires. Could you charge for it? Dunno. What happens reputation-wise if one of those fails soon after you had the amp on your bench? You know how that goes---all you have to do is to touch the thing and you own it.

[BrianS]

 ^

From what I saw on the last HRD I worked on, the pics I posted look like the start of what I think you are calling a "circular failure", as in the joint cracks in a circle all around the through-hole.  Maybe the heating and cooling of the PCB causes it to flex, thereby weakening the solder joints?

What's good about this customer is that he is a friend of the person who's HRD I repaired about a month ago.  I think they could talk with each other and that may help the new customer make the decision whether or not to get the work done, as he can hear first hand what kind of problems the overheated resistors can cause.

Thanks for the insights.

[Cliff Schecht]

Fender underrated those resistors, that's part of the reason they fail. I usually up them to 10W and try not to use those ceramic sandcast resistors, they have a tendency to crack after so many heating/cooling cycles. The part obviously gets hot enough to also kill the solder joints, so again I up the wattage and as you mentioned elevate them off the board a bit.

As far as charging, I always add a little bit of money to the bill if I have to lift a PCB and get underneath it. Like $20 on top of whatever else because of the additional amount of time it takes to do so. I'd have this repaired and back to the customer for $60-80 if the only issue is those resistors.

I did fix a HRD that randomly breaking into oscillation. The issue ended up being faulty electrolytic caps that were leaking after only a few months of use. The caps said they were made by IC (Illinois Capacitor) but I honestly think that they were counterfit. The labels on those caps were different than what every other IC cap I have and obviously they failed prematurely which has never happened to me anywhere else with IC stuff. I asked some of my older EE friends if they've had issues with this company and they said that they haven't. Long story short, double check that the caps don't have any puffiness or electrolyte gel leaking from the sealed ends!

[BrianS]

^Thanks for the tips, Cliff.

[Jack1962]

What I do with these amps and all the other amps I work on is I repair what has failed and I advise the customer of future problems that may occur. It has be my experience that most customers just want there amps working , most of them aren't very interested in spending money fixing what hasn't broke,,,,, yet .

[Cliff Schecht]

What I do with these amps and all the other amps I work on is I repair what has failed and I advise the customer of future problems that may occur. It has be my experience that most customers just want there amps working , most of them aren't very interested in spending money fixing what hasn't broke,,,,, yet .

This is probably why I'd never be a good full-time amp tech, I won't send equipment out knowing it's going to break again. I'm not after peoples money so much as I am building relationships with local musicians and collectors. Also, especially when you service that first amp for a new customer, you don't want your repairs even appearing faulty because something else down the line failed. Ideally nothing will fail catastrophically because of the safeguards in place (protection/limiting resistors, fuses and the like) but making sure that first repair actually takes is a great way to start building trust between yourself as an amp tech and the local musicians. It's pretty embarrassing when your repair fails in the middle of a gig and the customer is usually not so happy..

[BrianS]

The customer agreed to the "preventative" maintenance, however I am now losing my a$$ because there is already some damage to the solder pads of R97...both pads quickly lifted as I was unsoldering the resistor.  The joints looked "cold", and the resistor looked pretty cooked...I couldn't leave them as they were.

I'm sure there is some old proverb regarding good intentions that is applicable here...

[thermion]

What are the PM action items that you are charging for? PMs typically replace parts deemed consumable by the manufacturer to preempt their failure and verify optimal performance of non-consumable parts.
I think you may do better selling amp insurance/ extended service agreements with specific cost caps in place and plenty of clauses about operator negligence/ failure and the perception of how something sounds (ie. amp functions properly but customer complains it doesn't sound "good" or "right"). If you do go this route a reading of the Magnuson-Moss act may be a good exercise.
FWIW, future failures in vacuum tube circuits (and most everything else in life including yourself) are not a matter of if, but when. Period.
Best of luck!

[John]

The customer agreed to the "preventative" maintenance, however I am now losing my a$$ because there is already some damage to the solder pads of R97...both pads quickly lifted as I was unsoldering the resistor.  The joints looked "cold", and the resistor looked pretty cooked...I couldn't leave them as they were.

I'm sure there is some old proverb regarding good intentions that is applicable here...

The easy fix is to jumper a short wire to the trace, and take it down through the pad, or up through as the case may be. Remember, the traces and pads are just really very flat wires and turrets. :) Explain to the customer what you had to do, and make the job as neat as possible.

[BrianS]

"What are the PM action items that you are charging for?"

Honestly, I'm only several months into this business, as far as amp repair goes, and have only been in business for myself part time for a couple years with guitar repair.  As such, I do not have a service plan or "action items" for amps.  Guitar repair is a larger part of my business and I do have individual prices for those various jobs, which does make it easier for the customer to understand what they are paying for.

"The easy fix is to jumper a short wire to the trace, and take it down through the pad, or up through as the case may be. Remember, the traces and pads are just really very flat wires and turrets"

Yep, that's basically what I did.