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Author Topic: Fender 85 Issues - No sound sort of...UPDATE - No Power  (Read 374 times)

edjohansson

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Fender 85 Issues - No sound sort of...UPDATE - No Power
« on: November 12, 2017, 09:24:24 PM »

Hi there, first time poster. I've been reading the different topics here to try and trouble shoot my problem, but I'm stumped.

I bought a Fender 85 off Ebay, and when it arrived I couldn't get any sound through the speaker, just a low hum. Here's what I've tried:

1. Tested the speaker with a multitester and it is functional.
2. Tried each input (this one has 2) with different cords and different guitars that work on my other amp.
3. Tried running a cord between the effects loop inputs, no sound.
4. Tried using with headphones, no sound.
5. Tried running my iPhone through the inputs, very faint sound through both and the volume would go up and down.
6. Tried running my other amp (Yamaha THR10X) through the effects loop and got sound through the Fender speaker! But then the fuse blew.


I have a schematic for a Fender Deluxe 85, but very low knowledge of electronics and only a multimeter to test.

Are there any ideas as to what the issue is?
« Last Edit: November 14, 2017, 02:52:09 PM by edjohansson »
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edjohansson

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Re: Fender 85 Issues - No sound sort of
« Reply #1 on: November 13, 2017, 10:29:57 AM »

I have attached pictures of the board, the front of the amp and the closest schematic I could find (Studio 85). The amp was apparently functional before shipping but not now.
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solderdripper

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Re: Fender 85 Issues - No sound sort of
« Reply #2 on: November 13, 2017, 03:18:06 PM »

Hi Ed, I don't think I am very far ahead of you in skill, but I think I can offer you some starting advice.

Worked before he shipped it, huh?  :o  Well if you say so...  :)
The only things I can think of that would be affected by a simple shipment, or things that can be temperamental, are wire connectors, jacks, and pots.  From the diagram, it looks like those input jacks have a lot of switch going on. I would try some continuity tests or resistance checks through a guitar cable - e.g. one probe on the tip of the free end of the cable, the other to the jack's output pin (#2) - and also through the closed contacts on the input you're not using.

From where you are now, #1 question would be, Is it even the right fuse?  Hopefully there's a label on the board or chassis, make sure you get correct replacements, and buy a few.

The bottom left of the diagram seems to show the power supply circuit, it has some test points with values marked "VDC".  After you get a new fuse, you can check the supply. Connect multimeter ground to chassis and check the DC voltage at these points to see if your supply is.. supplying the proper voltages.

If those look ok, you can try to isolate the problem to preamp or power amp.
Connect the ipod to one input, then run a cord from the PREAMP OUT over to the POWER AMP IN on your Yamaha amplifier. Power them on and see if the preamp in the Fender is passing the signal.   I think this is similar to what you did already? Did you use a 'preamp out' signal from your Yamaha into the "POWER AMP IN" on the Fender when you did that?  One thing I've learned, jacks and pots are the most suspicious things on a used amp. Wiggle everything to try to make sure it isn't a scratchy pot not letting the signal through, or a stubborn jack.

If you don't get anything through the preamp, you can check the voltages at the supply pins on the ICs in the preamp path; if those look good, you can set up an audio probe and see if you can follow the signal through the circuit to find how far it gets.

That's probably long enough for starters, and will get some more information for others to consider.   Get the right fuse; check proper connectivity on all of the pins on the input jacks before trying the amp again.

Hope this helps!
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DrGonz78

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Re: Fender 85 Issues - No sound sort of
« Reply #3 on: November 13, 2017, 03:29:02 PM »

Not quite sure how you went about running signal from the Yamaha into the Fender? Just hope you did not plug speaker output from Yamaha amp into any of the inputs of the Fender. Probably you just sent line out signal into the power amp in on the Fender but just have to put it out there.

Blowing fuses is not good. Of course double check the right value of the fuse as solderdripper suggests. However, I think you need to be cautious going forward and even research how to make a light bulb limiter. This will prevent the amp from blowing fuses again and give you the ability to trouble shoot the amp.
https://www.ssguitar.com/index.php?topic=2093.0

At this point the hum you heard could have been DC voltage present on the speaker output. Do not connect a speaker to the amp until you know that there is 0v DC on the speaker terminal connections. If you put in a new fuse and it does not blow then measure DC voltage with your meter on the speaker terminals, again no speaker connected. If the fuse blows right away again then build the Light Bulb Limiter to proceed with the repair.
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A person who never made a mistake never tried anything new. -Albert Einstein

edjohansson

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Re: Fender 85 Issues - No sound sort of
« Reply #4 on: November 13, 2017, 09:44:27 PM »

Thanks to the both of you for the explanations, it really helps moving forward!

I bought a fuse exactly like the one that was in the amp, but I will check the chassis. I also picked up the supplies for the light bulb limiter, as I figured I would need it.

The Yamaha amp has an input jack and a headphone jack, so I was utilizing those to test the effects loop. Hopefully that wasn't a mistake.

I will try all the suggestions and post what I find. Can't thank you both enough for all the help.
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edjohansson

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Re: Fender 85 Issues - No sound sort of
« Reply #5 on: November 14, 2017, 11:52:04 AM »

Looks like I purchased the correct fuse, as it matched what was on the chassis. Put it in but now no power, I will look at the other posts to see how to trouble shoot this.
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phatt

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #6 on: November 15, 2017, 06:25:25 AM »

Hi Ed,, Check TP1 and TP2,, (marked on schematic) you should read ~30Volts AC (from common to either red, Red with yellow stripe is common). If no reading then check the fuse,, although it maybe new it may be a dud. 8|
If fuse is intact check you have continuity at both ends when installed on PCB holder,,
!!!!! But Pull the plug out of the wall FIRST as this is mains voltage side of the Tx !!!!!!

Once you have power,, all the test points are on the schematics and should be checked.
Phil.
« Last Edit: November 15, 2017, 06:42:20 AM by phatt »
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edjohansson

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #7 on: November 15, 2017, 12:48:29 PM »

Thanks for the info Phil, but I want to make sure I am testing right. Do I pull the transformer terminals and test for voltage or do they need to be plugged into the PCB board to be tested? I did pull the terminals and tested and there is no voltage across the terminals. The fuse had blown as well, so I think I need a light bulb limiter in order to do further testing.
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phatt

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #8 on: November 16, 2017, 06:48:18 AM »

Just start at the input and work through from power plug to Tx primary/ then Tx secondary.
I've had amps with a broken connection right inside the mains plug,, also had a main switch go intermittent (drove me nuts) so consider the whole electrical path.
YES if the primary is working then you can pull the 3 red secondary wires and read AC volts directly on the spade plugs
About 60 VAC between the 2 reds and half that between either Red and Red/Yellow stripe.
 
The fuse is Obviously on the primary side so if the fuse is good and you can't get voltage on the secondary then follow the pcb path of that fuse and the power switch interconnect wires. The power switch could be faulty, the fuse mounts are PCB mounted so tracks underside may be cracked or burnt out. Those pcb spade connectors might have cracked solder pads underside as they take a fair bit of stress when you pull them on and off many times.
A case of follow the path of the circuit which can be quite confussing for the novice. :duh
I actually don't like the idea of having mains tracks on the same PCB as the audio but it's done to save cost.
Phil.
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edjohansson

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #9 on: November 16, 2017, 01:42:26 PM »

Thank you yet again for the advice! I built the light bulb limiter last night, so the fun will begin tonight. All of the tips above should keep me busy for a while  :)
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phatt

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #10 on: November 17, 2017, 12:09:16 AM »

Tiss good you built a Limiter but before you can use that you need to establish the primary input path,, which is mains cord > power switch > and fuse. Sometimes the fuse is Before the switch,, sometimes after.

And for Gods sake remember to pull the power cord out of the wall before you go poking inside. Way to easy to to get excited when you finally find the fault and forget to unplug.
Please note the lightbulb limiter won't save your life,, Mains voltage can still kill you.
LEFT hand behind your back when working on live gear.
no watches, no rings, no dangle bracelets or necklaces. :trouble :trouble :trouble
Phil.
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edjohansson

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #11 on: November 18, 2017, 10:07:47 AM »

I will be testing more today, I bought a continuity tester but it was faulty so I have to exchange it. Once I have that I can test for continuity in the plug, switch and fuse. I will have to take the PCB off the chassis to see the solder points underneath as well. My multitester doesn't have continuity testing, but could I test for continuity using the ohms setting (for future reference)?
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phatt

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #12 on: November 18, 2017, 10:37:09 PM »

Yes just use the low Ohm setting on the meter,, obviously it won't read Zero as there is always a little resistance and a lot of meters are not accurate at very low ohms.
The leads will have some resistance so Self test the meter first by shorting the probes and if it reads 2 Ohms then subtract 2 from your readings.
Most meters come with a diode tester which is also a way to test continuity, often they have a beeper built in which is handy but use the low Ohms setting to be sure.
If you kept the instructions for the meter it will tell you how to use the functions.
Phil.
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edjohansson

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #13 on: November 19, 2017, 07:51:28 PM »

I've checked for continuity through the plug/switch/fuse and all is good there. I went to test the first two test points, but I am not getting any ac readings through them. As I am a noob, I want to be sure I'm testing right.....do I put the black end of the multitester to the chassis ground and the red on the metal part? Or do you test on either side? I attached a pic to show what I'm looking at, it's in the middle of the picture.
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phatt

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Re: Fender 85 Issues - No sound sort of...UPDATE - No Power
« Reply #14 on: November 20, 2017, 01:27:17 AM »

Power OFF and pull the plug from wall. pull the two red leads,, plug your probes into both ends,, set meter to AC volts,,, turn on the power and you should read around 60 Volts AC between the two Reds. Then test between one Red and the Red with yellow stripe,, you should read half that voltage. (same for other red)
If that all works then reconnect the wires and power up with light limiter and you can  move onto check the DC voltage test points. :tu:
Phil.
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