Incoming Yamaha 410 Amp with 'crackling' issues...

[Amp]

OK lads. T- 10 hours and counting, picking up one of these.



... unsure yet if it's a 50w or 100w version, late 70's/early 80s 410 solid state with  intermittancy issues. Based on his explanation, mostly sounds like contact stuff. SS Jazzers are my weakness, these are very highly regarded from a tonal standpoint, the price is right for the relatively long drive so I'm diving in.

Prepurchase Question 1: Anyone familiar with these from a repair standpoint?

Prepurchase Question 2: Anything specific I should look for from a behavioral standpoint that perhaps should cause me to pass on the amp all together?

Presuming the amp is a go, I'll post further details here with detailed pics as soon as I get it home later this evening.

[J M Fahey]

1) Enzo is King.
By the way, he's also the kind soul who posted most Guitar Yamaha schematics online, go figure.

2) just plug your guitar and play.
Loud, quiet, move the controls, listen for speaker buzz, etc.
Test the reverb, move switches.

[Enzo]

Well, thank you.  next time I am in Argentina, I'll buy you a cerveza

AMps are amps, I look at them all the same way.  Intermittant?  Check loop jacks or power amp in jacks, anything that interrupts the signal path when in use.  Check the input jacks. loose or cracked solder.  CHeck solder on all the controls along the panel.

Ball up your fist and whack the top of the amp, if it reacts, cuts out, comnes back on, or crackles, then you have a loose connection inside.

And it works or it doesn;t.  The speaker is not ratty, the amp is not full of hum, the features work.  No special tricks to checking out an amp.

[Roly]

My experience with faulty gear is that just about everything is repairable, and it's a very rare one that is so bad you wish you hadn't.  When buying, obvious faults are good because they demolish the asking price, and as Enzo implies, a fault that sounds like a road accident, blerts, farts, pops, rumbles, cutting in and out, are almost always due to dirty contacts, broken solder joint, just dumb stuff.

If it makes any sort of sound at all it's a good bet, and any faults are leverage to knock the price down.

Yammy stuff is normally well designed and built, so unless a cloud of smoke come out I say go for it.  :dbtu:

[Amp]

Well, here she is.
Decommissioned from a local junior high school bandroom closet, straight off a 20 year hiatus. I paid $85 for the amp plus $15 worth of fuel in the big V8 top go get it, so figure I'm in at 100 on this one, which I'm comfortable with at this stage. That leaves me budgeted $50 for parts before I'd get uncomfortable.

The intermittancy is coming from this.



When I tap it, I get signal. It was somewhat loose as far as the screws that held it to the chassis, I tightened them up but it's still causing intermittency and requires 'tapping' that specific part to get signal. Sometimes, when I turn the amp on, I get hum that dies out to clean after 5 seconds or so, tap on that a couple times, I get signal. Plays fine.

So, somewhere therein is the culprit. I'm guessing it's just a connection issue.

Where to start?

[Enzo]

I suspect if you look, there will be two large bolts through the heat sink to hold it to the chassis. That is your power amp module.  It plugs into the main board via a connector, maybe 6 or 8 pins in a row?  Check the solder on both the module pins and the mating connector pins on the main board.  And check that none of the female pins are spread loose.

But also be aware that every time you tap that thing, you are also sending a vibration through the rest of the chassis.  SO get out a wooden chopstick and start pushing things around.  The speaker plug next to it could be loose for example.

[Amp]

Good deal Enzo.
Will get to it ASAP.

The real problem here is that they put a tall and narrow 410 amp in a junior high school band class on casters. Incredibly, incredibly unstable arrangement that was meant for a frame, not wheels. Breathe on it hard and it threatens to tip over.

No doubt this puppy took a few spills and some connection got kicked loose.

I'll report back with pics once I start getting things taken apart.

[Roly]

Plays fine.

So, somewhere therein is the culprit. I'm guessing it's just a connection issue.

Where to start?

a) that puts you miles ahead, and for $100 it's a steal.

b) Yes.

c) LOOK.  "Your best service instruments are your eyes."  Get the chassis up on the bench, bright light, lens to hand, and gently wiggle the lose bit(s) and OBSERVE.  As Enzo says, this won't be "electronic" as such but a mechanical problem (as so many are).  Your analysis of how this fault came about (castors, unstable, falling over) sounds right, so concentrate on what would have been stressed when it got to ground zero forwards and backwards, and it's Sydney to a brick that will be where the trouble is. {ye gods, you could pay $100 just for one of those speakers - excellent score  :dbtu: }

[Amp]

Thanks Roly  :dbtu:
I'm quite happy with it. Its late here and I didn't quite get to poking around in it today, but definitely will tomorrow and will post extensive pics.

@ Enzo

It was precisely as you said, removed those bolts, 6 pins, power amp module came off. Put it back on, amp stayed 'cut out' so the problem is definitely somewhere in the amp module itself or in the connection between the PAM and the board.

One thing I'm quite curious about; the chatter I read on the internet about these is extremely limited and fragmented, nowhere near robust enough to trust. Its said that the Fifty-410 is a 50 watt amp, however on the reverse of the amp, right here:



...it says 120 watt? It certainly is loud as all get out. Perhaps I'm confusing something, or perhaps the internet is confused?

[g1]

  That sticker is specifications regarding the incoming power from your wall outlet.  It will tell you voltage, frequency, and power consumption of the amp.  So in your case the amp uses 120 watts from the wall (to deliver 50 watts to the speaker, not very efficient).

[Roly]

not very efficient

...but typical of Class-AB amps which run between about 50%, and 72% for Class-B with pretty terrible crossover distortion (which is roughly the difference between "hot" bias and "cold" bias; clean and inefficient to dirty and efficient).

[Amp]

OK, think we're home free.

Took out the guts



Turns out the pins for the power amp module weren't making good contact due to grime.

Here's my attempt at taking a pic of them through the lighted magnifier lens



Cleaned those, reassembled and now is consistently and reliably giving me full operation out of the left two speakers.

Anyway, now I have to wire up the two speakers on the right hand side.



You can see the improvised alligator clip arrangement they were using, doesn't work. One of the tabs is broken off (top right speaker, etc).

How do I figure out what wire I need to buy, what little clips I need to get, etc?

[J M Fahey]

You may make a new terminal bridge out of a piece of PCB, but to connect the terminal to the VC wires,you'll need some of the ultra flexible one (tinsel wires?) specifically made for that use.
You'll have to get it from some speaker repair guy, it's stuff not sold over the counter at Electronics shops.
Do not place it neither too tight (you'll tear it from the cone) nor too slack, where it may bump against the cone or even worse, short against the frame.
Place it in an "S" shape.

[Amp]

There's got to be an elegant way to do this.

Here's the wiring scheme, as best my limited knowledge and understanding would allow me to draw with MS paint.



So, the black and white wire descend from the plug in the chassis and hook into the terminals as seen. Everything is sane and logical until the wire flowage goes from the left bank (which receives direct power input from the plug and is presently functional) to the right bank (which is presently non-functional and presumably, receives indirect power input from the left bank)

Here, we now have an erratic series of mish-mash wires twisted together, alligator clips, phantom colors...

For example, the white wire that flows from the plug to the top left speaker, another white wire to the bottom left speaker then becomes a black wire twisted off on the wire terminal and that is just dangling loose, connecting to nothing.

Anyone know the proper speaker wiring scheme here?

[Roly]

Yorg!  First thing, loose wires in the speaker circuit are an invitation to a short and a dead output stage.

Not knowing what the speaker impedances are I can only guess, but if they are all 16 ohms each it is most likely that they are all simply connected in parallel, all the "+"'s together and all the "-"'s together (which is implied in your drawing by both output leads going to the first speaker).

However I'm concerned about the phasing; when speakers are mounted with their tag strips together like this the + and - will be on opposite sides, meaning that the vertical connections should cross over.  The tags should have a "+" or spot of red paint on one of the connections to indicate the phase.

Can we get a circuit to settle the matter?