Fender deluxe 90 problem

[johnguitarmcgoo]

Hello,
I have bought a Fender deluxe 90 for "spares or repair". Serial number M914104 Type PR 402
The bloke I bought it off said it was working fine, until he smelt a Burning smell coming from the amp.
It was the loudspeaker which he has thrown out, so I dont know if it was upgraded or stock.
I have looked around the PCB for signs of heat, but cant see anything. The fuse has blown, and I havent plugged it
in yet I thought I would try here first for advice.
Has anyone had this problem or similar with this type of amp.?
Thanks John Mc. Warrington England, UK.

[Enzo]

Speakers do not burn up on their own. Chances are the amp is producing DC on the output, and we certainly would check for that before connecting another speaker.

It worked until he smelt it burn up? Well, everything works until it doesn't.

Most bad parts do not look any different.

Have I seen blown amps? Yes, thousands of them.

[Jazz P Bass]

Welcome to the forum.

Here is the schematic: https://bmamps.com/Schematics/fender...ice_Manual.pdf

There is also a Deluxe 90 DSP, so you need to know which one is the correct one.

https://bmamps.com/Schematics/fender...ice_Manual.pdf

Keep in mind that when you are sourcing a replacement speaker (after checking the amp) that the Deluxe 90 uses a 4 ohm speaker.

[johnguitarmcgoo]

Thanks for the reply.

[johnguitarmcgoo]

Thanks for the reply, it is not the DSP it is just Deluxe 90.

[g1]

Can you read schematics? What kind of tools & test equipment do you have available? What is your level of repair experience?

[johnguitarmcgoo]

Can you read schematics? What kind of tools & test equipment do you have available? What is your level of repair experience?

Hello, thanks for the reply. I have basic knowledge and repair skills ie, I could desolder and replace a part if I knew which part. I have a AVO style multimeter that will measure Resistance , volts continuity , polarity, amps. I was hoping someone may have had similar problem and say "hey it is this ". I do have a speaker 4 ohms 60 watts to connect up to try, but thought I would ask here first. Any advice is better than none.

[Enzo]

Doesn't work that way. Your problem is generic - amp doesn't work, blown speaker, etc. It isn't going to be one thing all the time. In fact, you may have a bad output transistor, but there are two, and it could be either one. or it could be either driver transistor. or an open resistor, or any one or more of 25 other parts. It might not even be a bad part, you could have a broken printed circuit board trace or a failed solder joint doing this. So this is like asking "my car won't start, which part is bad?"

You need to work with NO speaker connected until we know the amp is stable. First thing to do is determine if DC voltage is across the speaker wires.

[johnguitarmcgoo]

Hello Enzo, I was hoping that it was a broken track or dry joint as I could have spotted that. It is not worth taking to a Technician as over here in the UK. they are very expensive. If all fails I will use it as an extension cab for my 30w valve amp so not a complete waste of money.

[johnguitarmcgoo]

Doesn't work that way. Your problem is generic - amp doesn't work, blown speaker, etc. It isn't going to be one thing all the time. In fact, you may have a bad output transistor, but there are two, and it could be either one. or it could be either driver transistor. or an open resistor, or any one or more of 25 other parts. It might not even be a bad part, you could have a broken printed circuit board trace or a failed solder joint doing this. So this is like asking "my car won't start, which part is bad?"

You need to work with NO speaker connected until we know the amp is stable. First thing to do is determine if DC voltage is across the speaker wires.

Hello, I have replaced the fuse and fixed the reverb unit (black wire on input side not connected inside mini plug). Switched on the power, and it turned on. There is 121mv across the speaker wires, white is +. Is this abnormal?
I switched it off after 2 mins.

[Enzo]

I don't start to concern myself until teh DC offset gets over about twice that amount. 120mv sounds OK to me.

[johnguitarmcgoo]

Update, I connected the speaker and switched on, it hummed and started to smell warm so I switched off.

[johnguitarmcgoo]

Successful update

Update, I connected the speaker and switched on, it hummed and started to smell warm so I switched off.

Hello all, I have now fixed this problem. It was a dry joint on resistor R145. Simply re soldered and it now works fine. I have had to fit an 8 ohm speaker, but I,m hoping to find the correct 4 ohm on ebay.
Thanks to all for your help.