Rumble 200 turned out to be eggshell fragile

[elgranluis]

Techs often see folly that designers overlook. Today I was over at my dad's and he asked me to put away a Crate guitar amp that he had sitting in his shop. When I picked it up, I noticed that it had a level control knob for the line output sticking way out from the back panel, just waiting for something to shear it off.

I thought if I had a hand in designing it, I would have located the control closer to the cabinet edge where it would be better protected and use a low profile knob. However, when the guy was designing this PC board, I doubt he was thinking of such and event taking place.

Perhaps someone had replaced it already with a longer shaft ?

 

[Mike Whitfield]

Which board? The power module doesn't have external jacks directly mounted to it, so I'm confused as to exactly which PCB is broken. It seems that quite a few people call the power module boards motherboards (which seems a bit wrong to me, not that it matters much), just want to make sure I'm on the same page here.

Isn’t there an I/O board with all those jacks? I would assume it’s that. Although it is rather surprising that a $500 amp isn’t worth replacing that board. Must be more to it than I would have guessed. But then, I’ve never owned a $500 amp or had an amp repaired so it’s hardly surprising that I’d guess wrong.

 

[agedhorse]

Doesn't your amp have metal bushing jacks with nuts? If so, I have impact tested those jacks as an assembly and to crack the PCB behind the jack is going to take a hell of a lot harder hit than a "gentle bump" I'll bet the sheet metal behind the jack is bent as well.

 

[byacey]

Perhaps someone had replaced it already with a longer shaft ?

Not unless they also procured a knob that matches all the others on the amp. This particular control doesn't need adjusting often, so even just a knurled shaft sticking out a 1/4" would have worked well.

 

[5StringBlues]

SHAFT!

Can you dig it?



I mean, uh, subbed.

 

[seamonkey]

A picture or few of the broken board would help satisfy my curiosity.

Even auto dealers with mail a photo of damage when quoting a fix. (Car analogies are required around here )

 

[Mike Whitfield]

Doesn't your amp have metal bushing jacks with nuts? If so, I have impact tested those jacks as an assembly and to crack the PCB behind the jack is going to take a hell of a lot harder hit than a "gentle bump" I'll bet the sheet metal behind the jack is bent as well.

Have you impact tested on a side load? I could see the cabinet striking the jack, flexing the jack hard enough to slip loose from the jack, and continuing on its slide without seeming to slow down. Wouldn't that be pretty much worse case impact load? I can see that breaking the board.

 

[Lowandfat]

With all this talk about egos, I am struck by the fact that when something bad happens, it's always someone else's fault. Also, some people think their opinion is the only correct one that counts...others are not entitled to theirs.

Who said it was someone else's fault? Crappy components, minor blow, dead amp. That's all that happened. Also, in this case I do believe the opinion of the OP who has the info and made the decision, and the a-list tech who took it apart and diagnosed the fatality, are worth a lot more than some internet armchairtech who declares "I know more about this than you, and your tech is a hack." No, they don't, Mike is not a hack, and to assert one knows more about the details than the people who know the details is silly, and should be treated as such.

 

[Lowandfat]

For those inquiring, I sent a message to my friend doing the removal to take some pics of the damage. From what I understand from the original diagnostic, the sheet metal was slightly bent around the jack, as you suggested Andy, but I don't know how extensively. This could better explain the crack. For those saying it's worth fixing, that might be true, but for what I have into it, the fact it is lower power than I need for the gigs I would use it for, that the bench it was opened up on was more costly than other options I have, that I have plenty of other gear that does the same job better, all made my decision for me. You might have chosen differently in the same predicament, but I have the components on hand to try this experiment, including 2 other speaker options beyond the one in there, and 2 class D heads with double the juice or more, so why not? The worst thing that can happen is I sell it for parts.
Bonus: My cost for hours on the bench that it's on now is a few lunches, and I have to help.

 

[agedhorse]

Have you impact tested on a side load? I could see the cabinet striking the jack, flexing the jack hard enough to slip loose from the jack, and continuing on its slide without seeming to slow down. Wouldn't that be pretty much worse case impact load? I can see that breaking the board.

The impact would have to be substantial enough to bend the sheet metal and the plug would have to be in the jack too. Generally (but not always) with side impacts, the jack will break rather than the PCB. The pattern left in the sheet metal tells the rest of the story.

Forensic electronic analysts is something that I do regularly as part of fault analysis. It's done in order to improve the long term reliability of products.

From my experience, Fender generally does a good job with this. There are plenty of smart guys working there who know their stuff.

 

[lokikallas]

Where did this impact happen? On stage, in transit, or in storage? If it was anywhere but on stage, a tuki cover on the amp, and or offending monitor might have saved the day.

 

[Mike Whitfield]

The impact would have to be substantial enough to bend the sheet metal and the plug would have to be in the jack too. Generally (but not always) with side impacts, the jack will break rather than the PCB. The pattern left in the sheet metal tells the rest of the story.

Forensic electronic analysts is something that I do regularly as part of fault analysis. It's done in order to improve the long term reliability of products.

From my experience, Fender generally does a good job with this. There are plenty of smart guys working there who know their stuff.

Given the OP's description I can't imagine the cable was still plugged in, and even I've heard of Mike Finck. He's one of the best in the audio technician business, known across the East. (I had no idea he worked on $500 amplifiers though; maybe it's not the same guy. I actually know a Dr. Mike Fink who's one of the world's leading experts on hellbenders so there could definitely be two Mike Fink/Finck audio techs.) So I guess the impact was either a one in a million, just the perfect angle and perfect height to catch the jack at the weakest possible angle, or it was a LOT harder than the OP realized. Also, the OP wasn't entirely pleased with the amp anyway; someone entirely pleased with the amp might well have shrugged and repaired it rather than taking this as an opportunity to make something more suited to his own needs.

Assuming the tech is THE Mike Finck, it probably isn't worth his time to repair in any case. And if Lowandfat earns his living with this amp, I seriously doubt he's be interested in having some jackleg epoxy and solder over the traces on a broken board like some weekend warrior or bedroom/basement/office pretender. (No insult intended, I'm a committed office pretender myself.) In any case, I think you've put to bed the idea that Fender is making something that's more fragile than is appropriate for this price point.

 

[Nevada Pete]

I am not even going to bother to read that, because you obviously haven't even bothered to read the thread. Lighten up Francis.

Whatever you say, boss. Just trying to help you out. That's all. I'm a very busy guy. Not sure how you can be offended if you didn't read my post though. Good luck.

 

[Lowandfat]

No one is offended, just a glance at your post shows you didn't read the thread. Enough time to write an essay, but not enough time to read the conversation. Whatevs.

 

[Mike Whitfield]

No one is offended, just a glance at your post shows you didn't read the thread. Enough time to write an essay, but not enough time to read the conversation. Whatevs.

So is this the guy that is up in the Northeast, works on the multi-thousand dollar audio systems around the New York market IIRC? Or just another certified amp tech with the same (or almost same) name? Pretty sure the guy I'm thinking about spells his name "Finck".

ADDIT: Actually I just remembered that the professor at Lee College isn't named "Fink", but "Freake". Old brain moment.

 

[Lowandfat]

Yes, it's that Mike from Hi On Fi, and he is a friend who fixes broken things I ask him to fix. Just a few years ago he did a full rebuild on my dad's 60s era Mac MC-60s, and most recently replaced some broken bits on a Mackie 808-s for me. Good to have friends like Mike. I really don't get the assertions here that he somehow doesn't know what he is doing from people who didn't see the damage. Sure, the blow may have been more substantial than I realized, but why is that a point for attack, and what does it have to do with the rebuild we are attempting. The question as to whether TO ME it is worth repairing has been answered multiple times, and the need to make this thread combative on these points is frankly baffling.

 

[Lowandfat]

I honestly had no idea he spelled his name with a c. Never had reason for him to write it down for me lol. Known him for 20+ years.

 

[Lowandfat]

I don't think Fender gear is the issue overall, but they have shipped Blue Jrs with similarly fragile jack assemblies for decades now with little to no improvement to that stress point.

 

[Mike Whitfield]

Yes, it's that Mike from Hi On Fi, and he is a friend who fixes broken things I ask him to fix. Just a few years ago he did a full rebuild on my dad's 60s era Mac MC-60s, and most recently replaced some broken bits on a Mackie 808-s for me. Good to have friends like Mike. I really don't get the assertions here that he somehow doesn't know what he is doing from people who didn't see the damage. Sure, the blow may have been more substantial than I realized, but why is that a point for attack, and what does it have to do with the rebuild we are attempting. The question as to whether TO ME it is worth repairing has been answered multiple times, and the need to make this thread combative on these points is frankly baffling.

That's pretty amazing. I didn't even know he worked on amplifiers like yours. Dude's kind of a legend.

I agree with being combative, and blows can be quite deceiving in force. We had a local NASCAR driver, Grant Adcox, who was killed in a race when his car simply struck the wall sideways. On film it looked like he barely kissed the wall when in reality, the car ended up something like ten inches narrower. I can totally see that an impact might look inconsequential when in reality it's a freak strike at exactly the right angle to do maximum damage with minimum apparent recoil. And I understand why your initial reaction might be that the amp is unusually fragile, given the behavior of the two bodies and that an impact with similar trajectories would be expected to cause no damage beyond a cosmetic blemish. We expect things to behave like they usually behave.

 

[agedhorse]

Yes, it's that Mike from Hi On Fi, and he is a friend who fixes broken things I ask him to fix. Just a few years ago he did a full rebuild on my dad's 60s era Mac MC-60s, and most recently replaced some broken bits on a Mackie 808-s for me. Good to have friends like Mike. I really don't get the assertions here that he somehow doesn't know what he is doing from people who didn't see the damage. Sure, the blow may have been more substantial than I realized, but why is that a point for attack, and what does it have to do with the rebuild we are attempting. The question as to whether TO ME it is worth repairing has been answered multiple times, and the need to make this thread combative on these points is frankly baffling.

I think the point being made is because of your thread title, and your description which doesn't match with my (and other's) experiences with reality.

I am familiar enough with your amp that I know it got hit plenty hard, and that it's 95% likely to be repairable by a qualified tech. That would be a <$100 repair in my shop for example, and none of my techs are "inexpensive". They are highly qualified, fast and efficient.