70's Fender DR Red plate fuse blown

[alien]

Hey

I dont know half of the term you used

But I just checked the output coupling(blue thingys) and the only position I was able to get any reading was the positive lead of the meter to the negative of the coupling and the negative lead of the meter to chassis. That reading on both couplings was 230k ohms

Every other reading was OL including across the coupling.

I dont know what the filter cap readings I posted in my other post mean yet. Isnt their a tech site somewhere with expected readings? I have searched for days.

[Enzo]

It looks very much like you have a main filter cap shorted. It is either the part itself gone bad, or there is somethiing touching ground in the wiring. For example a nut or washer that found its way under the part board.

[alien]

It looks very much like you have a main filter cap shorted. It is either the part itself gone bad, or there is somethiing touching ground in the wiring. For example a nut or washer that found its way under the part board.

Is that because of the readings I took?

If I unsolder them will that give me a more sure measurement?

I lifted the parts boards and there is nothing under them or inbetween

What does a shorted cap read?

[Enzo]

A shorted cap reads like a piece of wire.

If you measure resistance to chassis from some point in the circuit and get a .5 ohm reading, then that point is shorted to ground.

[alien]

A shorted cap reads like a piece of wire.

If you measure resistance to chassis from some point in the circuit and get a .5 ohm reading, then that point is shorted to ground.

Hey Enzo

I took the first 2 F caps off and one of them measures .2 ohms when I connect a lead to each end--the other one reads OL--so do you think that is bad?--and is it the primary problem?--or could something else cause the cap to be bad?


and about that 220 ohm thing we were talkin bout before..could that just be normal/..because with the filter cap out its reads nothing but when I put in a wire to complete the connection(without the cap in)..its still there. If I read the pins where those OT wires are hooked up they read 50 ohms

I still cant find any websites with FDR readings--this 1980 Twin OT should have
"
red to brown=36.3
red to brown/yell =5.1
red to blue=38
red to blue/yell=4.4
blue to brown=74.5
On your OTs secondary side you should have .3 to .4 across the black to green wire, and no more than .3 across the black to green /yellow wire"
says some guy ")

Update..this site said this
Fender Princeton output transformer is about 150 Ohms both sides, Deluxe about 200 Ohms both sides.

http://www.fenderforum.com/forum.htm...-02-2407:02:44

Am I reading this right because I have been racking my brain about this 220 ohms for days--so if its normal--man did I waste my time
thanks much

[alien]

anyone?

thanks

[Enzo]

If your filter cap reads less than an ohm, then yes it is shorted. Replace it.

If the 220 ohm thing goes away when the red wire is off, then the transformer is likely OK. If you like, measure resistance from each pin 3 to the red wire as it sits in the air. Do you get 200 ohms? Otherwise some cirtcuit resistance was involved.

[alien]

measure resistance from each pin 3 to the red wire as it sits in the air. Do you get 200 ohms? .

Hi

I get 220. But as I said in my last post a guy said that was normal(I posted a link)--is he wrong?

I ordered new filter caps with the same specs as the ones I have and those 2 470 resistors at the socket and a few other caps just in case

Thanks so far for all your help.


PS..I read something about modding the normal channel for more gain and a Marshall voicing---anyone know how this is done?

[Enzo]

No, he was not wrong. The point is this - your circuit is shorted to ground where the red wire connects. Maybe no physiclly at that exact spot, but electrically so. SO when the red wire is connected there and you measure resistance to ground from pin 3, all you are now doing is measuring the resistance of the transformer. Since the transformer measures 220 ohms from pin 3 to the red wire, and the red wire is grounded by the fault, then of course you measure 220 ohms from pin 3 to ground.

That is why I suggested you measure it - we demonstrate that the resistance you measured was eth same as the transformer itself. It is all thus consistent. You find out why that point is shorted to ground - shorted cap makes sense to me - and fix it, and the transformer will no longer measure 220 to ground. It will be OK.

[alien]

Hey

I put the filter caps in and it works(I bought new tubes too). The other ones were new as well--I havnt tried them yet

Thanks so much. My question now is--is there a risk at trying the other tubes?

The phase tube was the cause of the crackling so I took out the verb tube and put that one in and it went away. It sound so good

[darrellcheng]

I live in Long Island and I can give you a hand if you like

[darrellcheng]

Did you check and/or change resistors in the cap pan too? Also when you check you should refer to the schematic's original values. Make sure caps are oriented correctly (neg to ground). You should also go over the wiring, make sure all grounds are grounded using continuity function

[alien]

Hey thanks

I dont think my meter has a continuity function.

I didnt replace the resistors in the pan because they were to spec and measured right. But it sounds good..I just need to bias it correctly

[Enzo]

COntinuity means a complete circuit. Your ohm meter function does that. A "continuity" function just adds a beep or a light. If your meter has a diode test, that is probably also called continuity. We are talking digital meters now. If you have a little analog meter - the kind with the moving needle - then you are probably stuck with ohms .

[alien]

COntinuity means a complete circuit. Your ohm meter function does that. A "continuity" function just adds a beep or a light. If your meter has a diode test, that is probably also called continuity. We are talking digital meters now. If you have a little analog meter - the kind with the moving needle - then you are probably stuck with ohms .

Its digital. So what reading am I looking for?--and the amp plays and sounds real good so could I still have a short?

thanks