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Post subject: Schematic for Eighty-Five
Posted: Sat Jul 25, 2009 10:56 am
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Hello,


I am in need of the schematic for the Fender Eighty-Five 1x12 amplifier. I have had this amp for quite a while, but I haven't been using this particular unit.

I installed a switch an a 1/4" female jack for an external speaker, however, when I turn it on, it seems there is only real volume in the overdrive, on my 4x12 half cab.

I am not sure if I am just remembering how it sounds wrong, but "10" on the clean channel is equivalent to the loudness of "2" on the overdrive channel.


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Posted: Sat Jul 25, 2009 9:17 pm
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If anyone knows where I can get a schematic I would be so grateful!

Here is what is happening:

The overdrive channel sounds and works fine.

When I switch to the clean channel, I can turn it all the way up, and it's only maybe as loud as the drive channel is set at "1".

There was a leaky capacitor, C3, that I changed, and the clean channel got loud, (But still way under the overdrive channel) but when I tried it a second time, the volume knob suddenly is "reversed" and it is barely audible.

I have tried switching the volume pots on the overdrive and clean channel, but that did absolutely nothing.

I need help!


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Posted: Mon Jul 27, 2009 6:18 am
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This one should be close. http://www.perthwindsurfing.com/fender8 ... dio-85.jpg


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Posted: Mon Jul 27, 2009 9:50 am
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Thanks, that actually looks identical!

I am not sure, but aside from removing every component and testing it individually, the clean channel is still 1/10th the sound of the overdrive channel.

I have tested every resistor over 1/4 watt, the resistors that read .47 ohms read 2 ohms, but I think that is my meter.

I will study the schematic more.


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Posted: Mon Jul 27, 2009 1:23 pm
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Guys,

I have checked all the DC voltages it says to check, and every one checks out.

The "overdrive" light is faintly on and flickers to crackling in the speakers.

I have a question:

When it says all knobs at 12 o clock, and a 1 KHz signal input against an 8 ohm resistive load, what amplitude is that 1 KHz signal supposed to be?

I have a function generator, but as far as I can see, the schematic doesn't tell me how much power to put into it for the AC test points.


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Posted: Mon Jul 27, 2009 10:52 pm
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jchevalier wrote:


Hey man.. Thanks for the schematic! I've been looking for one for a while. Never could find one. Is this from a different model but similar type amp?


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Posted: Tue Jul 28, 2009 6:43 am
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I have been unable to find much information and received no response to a former post here but I think the Eighty-Five, the Deluxe 85 and the Studio 85 are very similar. The Deluxe had a 12" speaker as does my Eighty-Five and the Studio had a 10" speaker.

As for troubleshooting, I don't think the exact tone level is critical. Since the overdrive channel seems to be working, inject a tone at the input of the power amp stage and work backwards toward the input of the normal channel, turning the level down at each stage.

To me, the weakest part of the amp appears to be the jacks and trying to replace them without damaging the printed circuit boards, but that is common with all modern amps.


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Posted: Tue Jul 28, 2009 9:46 am
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Hello guys,

Fender emailed me the schematic for the Eighty-Five, and it is identical (Except for a parts list) to the schematic posted here. I believe the only difference is speaker size (Studio Eighty-Five has a 10" speaker versus the Eighty-Five which has a 12" speaker).

That's a good idea about working backwards. What do you mean by turning it down as I go? Should I check for the AC voltages on the schematic?

I have noticed that the flux I am using actually causes a great deal of interference if left on the motherboard.

I am going to keep trying to fix this thing. It is actually very loud driving a half-stack. I'd love to be able to play clean through it.


Thanks!


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Posted: Wed Jul 29, 2009 1:48 am
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Thanks for the information. I have a Studio and an Eighty Five, and all I gotta say is they're my favorite gigging amps.

We had a venue owner tell us one time "do NOT bring practice amps to the venue!" So I'm like, "ok man we won't I promise". We show up for sound-check and the bands that showed up all had 1/2 stacks. All I could think about was how much of a waste of space it was to clutter the spot where we had to unload.

The venue owner and the sound-guy come over and they're going over what's going to be back-line and what they're gonna have to mic up. They ask me what we have for our amp setups and I show him my 85s. Both guys start to fly off the handle. "I specifically said NO practice amps!! Those things are gonna sound like crap!"

I tell them both to keep their panties on, the amps are clean and plenty loud enough. They just roll their eyes at me and walk off talking s**t under their breath.

We had to set up and sound-check on the fly in between sets. Our band is pretty fast at it. And what's the first thing I hear??? Can you turn the guitars down a little?
What?? I've got it on 1 1/2 dude.. :twisted:

After the show both guys come over and tell me that our sound was killer and they didn't know these amps sounded as good as they do.

THAT'S RIGHT YOU DIDN'T KNOW!! SUCKAHS!! I think band #1 needs you to help them load their half stacks back in the truck.. maybe you can give them a hand. :D


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Posted: Wed Jul 29, 2009 9:15 am
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Hello guys,


Well, I took a lot of readings on the AC test points.

Every reading was completely off. Where it should have been 10 Mv, I got 15 volts. 1 KHz signal, test specs as stated on the schematic.

But I realized that I didn't have the motherboard bolted into the chassis, some of the nuts that go on the post act as a ground connection via the chassis.

So, after I replaced capacitor C3, and resistor R 86 (I think, 1 watt, 220 ohm), cleaning the motherboard, fixing connections, soldering things that should be soldered, I put it all back together.

And WOW it sounds better than it ever has!!

The clean channel is absolutely beautiful.

And, I put a 1/4" female jack in with a switch, so I can hook up an external speaker, and switch between the stock 12" speaker, and whatever speaker I have an external connection to (ahem, half stack, full stack. I have a Blue Voodoo 100W tube head, but I wanted to hear the Eighty-Five).

It sounds great! Better than ever! This is a GREAT amp, and like the guy said above me, plenty LOUD.

Thank you guys for helping me out. If someone can tell me how to post a file on here (PDF) I will post what Fender has sent me, so you guys can have a parts list, too.


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Posted: Thu Jul 30, 2009 12:12 pm
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I'm not computer savvy enough to know how to post a pdf.

Good job on your mods and getting it running again. The clean channel really is nice. I use a Tech-21 Tri OD for distortion. The amp is plenty loud enough. Definitely not just a practice amp.


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Posted: Fri Jul 31, 2009 10:30 am
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I hear you. Thanks for the kind words. It does drive a half stack pretty good (But the stack is 16 ohm so there is some distortion).

It's definately a great little amp. The only thing I am missing is one of the knobs on the front. Any idea where I can get one?


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Posted: Sun Aug 02, 2009 12:36 pm
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You can get 'em on ebay, but you usually have to buy 6 of them. If you only need 1, send me a PM with your address and I'll send you one of my extras. They're just laying around here anyway.


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Posted: Sun Aug 02, 2009 8:57 pm
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That is very kind of you!

Private Messaging has been disabled on this board it says.


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Posted: Mon Aug 03, 2009 3:31 am
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You know, I was wondering about that myself. I don't see an inbox, or signature section, or anything else in my profile.


Last edited by Shredd6 on Mon Aug 03, 2009 2:07 pm, edited 1 time in total.

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