yammy ax 470 (pt 2)

[harrydg]

Hey all,

I've got a question. I received a Yamaha AX 470 amp that is "broken". It plays still "rather well" but i've noticed a few things
2 of the 5 or so inputs have problems with the left channel as in: it cracks instead of playing music sometimes. The other inputs don't seem to have this problem
BUT also: after a while, the left channel gives more bass/depth and just sounds... not good. The right channel seems OK though.

I've been reading a lot around here that this may be the problem of the caps, transistors and/or relay. I'm off course interested in the repair, but the biggest question i have is: is it worth it? because if this is a crappy amp to begin with, it might be better to just let the owners buy a new one.
Since my last error on this amp (see earlier post), i've been doing nothing but reading up on how amps work etc... but i still don't know where best to start. If anyone here is from Belgium, and willing to help (me learn ), just let me know!

Thanks in advance, guys! (and women )

[Tekko]

A common item to foul up is the input selector, i had a yamaha receiver that would drop one channel after a few minutes, wiggle the input selector knob fixed it for a few more minutes.

However there can also be things like bad solder joints and possibly but very unlikely a broken transistor.

[nigelwright7557]

Electrolytics also start to dry up on old amplifiers.

[sakis]

the AX470 is a very good comercial machine but suffers from the usual problems of that time ...problems enough to convert it to an almost high end machine ....

worth upgrading a few parts nothing in transistors or so though and thats about it ...

[pinkmouse]

Two ways of looking at it Harry:

1) Is it financially worthwhile - will the cost of new components be smaller than the value of the repaired/improved amp? Possible, but unlikely.

2)Will it be fun and will I learn something? Much more probable, and I suspect the major motivation of most on this forum.

Only you can weigh the relative importance of the two factors.

[harrydg]

thanks for all the replies!
you are right, pinkmouse... the thing is just that i don't know where exactly to look or how to look. i thought, just feed it a "known" signal and check at certain points, but i don't have a scope to do this. i don't know (yet) what distortion exactly sounds like and so on. i just started on theories and schematics. Time to get practical!

so yeah, I think i'll definately try to fix it, just not sure on what to say to the "owners"... i changed my mind 2x already... no i can't fix it... yes i can... to no, i cant... after reading sakis' thread, i was inclined to try replacing all the caps (only of the amp part?) or also imputs...? The amp is about 10-15 years old, i think.
But then i started wondering, since it's only the left channel that (to me) has problems, maybe it's the relay that needs cleaning, or maybe i DID blow up transistors in my first "try to fix it"-attempt (see my earlier post on this amp)... So for me now... i do want to learn! i do want to have fun... but how do i best start the fun?

[harrydg]

Originally Posted by sakis

the AX470 is a very good comercial machine but suffers from the usual problems of that time ...problems enough to convert it to an almost high end machine ....

worth upgrading a few parts nothing in transistors or so though and thats about it ...

first i'll try fixing, then i'd love to hear on how it can be upgraded... hey... it's your thread (p3a comparison) that made me change my mind to... "i want to be able to do (a fraction) of that too!!!"

[pinkmouse]

First thing to do is to do some googling, (or contact Yamaha) to try and get hold of a schematic. That makes things so much easier.

Without a 'scope, you're a bit limited in what you can do, but I'd start by getting hold of some contact cleaner and cleaning all the switches and sockets, then go over the board with a magnifying glass looking for cracked or dry solder joints. Got any pics of the internals?

[harrydg]

the first part i already have for a while...
http://harry.enzoverder.be/YAMAHA%20AX-470%20SM--.pdf

the second part is a very good plan, i'll start doing that... and make pictures from the inside as well...
thanks!!!

[giannib]

It happened also to me, then tried to move the selector like " opening a broken keylock "
left-right push-pull; I found the source of the problem but not the solution.

I treated with anti-oxidants, even tried to open it

How did you manage it?

ciao

gianni