what happened? Yamaha bass head

TimmyGT · #1 05-19-2008, 01:04 PM

so I hadn't played my Yamaha B100 bass head in some time as I have a very nice Eden set-up. I pulled it out the other day to clean and rearrange my music room. So when I stopped using it, it was working perfectly but now I tried it again and it sounds terrible. I have tried a few different subs and cables that I have and they all sound the same so it has to be with the head unit. I looked into bringing it into a shop to get fixed and they wanted way to much just to look at it so I wanted to know what I should do!

so far I have tested all the fuses, there where 4 total (2 on the back and 2 inside) and they where all good. so then I tested the speaker plugs on the back and they where making connection.

I'm not sure what other steps I should take to find out whats going on! what should I check next?

here are some pics of the unit taken apart!

TimmyGT · #2 05-19-2008, 01:34 PM

so I have done a little more more testing and I think it might be the input jack thats bad. there is a resister on it that doesn't seem to be working. anyone know how I would test to to know for sure thats what the problem is? maybe how I would test a resister?

thanks?

ssbass · #3 05-19-2008, 01:50 PM

Quote:

Originally Posted by TimmyGT

so I have done a little more more testing and I think it might be the input jack thats bad. there is a resister on it that doesn't seem to be working. anyone know how I would test to to know for sure thats what the problem is? maybe how I would test a resister?

thanks?

use the color code to figure out what the resistance is then test with an ohm meter.

TimmyGT · #4 05-19-2008, 02:14 PM

Quote:

Originally Posted by ssbass

use the color code to figure out what the resistance is then test with an ohm meter.

they are like a 65 k ohm but one of them I'm not getting any reading! the other seems to be close @ 67.5 k ohms.

should I try to replace both anyways or just the one not getting a reading?

TimmyGT · #5 05-19-2008, 03:39 PM

ok so I just pulled both out and tested them again and they both seem to be working out of the unit so I put them back in and started testing both the high and low input for current and on the low side I am not getting a reading on the positive to the amp (see arrow in pic)

my next question is can I just replace the whole input unit or what should I do to fix this?

JTE · #6 05-19-2008, 05:17 PM

Those jacks that Yamaha (and Crate, and several other companies) used were pretty fragile. I'd replace the jacks if it were mine.

Is that the old original (late '70s) Yamaha B-100 with no suffix? It looks like the rear chassis, and I don't recall the Mk II or the MK III having the auxillary AC outlet on the back.

jte

TimmyGT · #7 05-19-2008, 08:36 PM

Quote:

Originally Posted by JTE

Those jacks that Yamaha (and Crate, and several other companies) used were pretty fragile. I'd replace the jacks if it were mine.

what types of jacks can I use to replace it with? and where should I get them from?

Quote:

Originally Posted by JTE

Is that the old original (late '70s) Yamaha B-100 with no suffix? It looks like the rear chassis, and I don't recall the Mk II or the MK III having the auxillary AC outlet on the back.

Yeah, I think my uncle got it in like 77-78 or something like that. he sold it to me in like 98 along with a Yamaha 150 II. everything has worked great until I stopped using it for a little bit!

JTE · #8 05-20-2008, 09:11 AM

I'm sorry, I don't know where to get the jacks any more. We used to get them from a place in Chicago called Music Dealer Services, but they went out of business years ago. I don't do amp repairs, but digging around the amp section might lead to some good sources for those jacks. They're a PC board mounted jack, and you'll have to not only unsolder the pins into the solder traces, but the jack housing mounts to the PC board and they used heat to melt the legs to hold the jack housing in place. Depending on how much room there is you MIGHT be able to install regular panel mount Switchcraft jacks. But be careful- some are switching jacks so you can't just use the regular one-conductor jacks.

You might be able to contact Yamaha for help with this. Back in the '80s they were one of the BEST and friedliest tech service companies we dealt with.

jte

TimmyGT · #9 05-21-2008, 11:09 AM

Quote:

Originally Posted by TimmyGT

so is there any reason I cant just remove this whole jack and just connect these (see arrow) leads to a normal jack? about the only thing special that I see about this unit is that it has the resisters on it but I am guessing that was for the hi/low input jacks.