Fender Rumble 500 Bass amp I only hear the fan nothing else ?

[Enzo]

So we feed it something imbalanced. All we want to know is if it will make noise or not.

[Jam]

What do you mean send it something imbalanced? So p103 has +25.4 VDC and -25.4 Vdc and on the ice power with the p102 unplugged I have+4.75 vdc on pin 2 and also on TP9 for {headphones } I got 0VDC. thanks again for any info

[Enzo]

Juan suggested we send a signal directly into the power amp, rather than through teh rest of the amp, good idea.

Then Jazz worried the input to the power amp is a balanced signal, wwhich woul dbe like a XLR microphone signal.. My counter was that since all we want to know at the moment is if the power amp can make noise or not, we need not worry about a balanced signal, we can just inject some sort of noise signal into the input in unbalanced fashion, and it woul dbe good enough for the test. That means using one side of the input as "hot" and grounding the other side. Or it might even work well enough to the test to just inject one of hte pins.

[Jam]

Thanks are you saying send a signal in to the ice power module ? Just testing the module? How do I do that?

[Jazz P Bass]

So now we have +4.75 Vdc at pin 2 of the ICE module.
Your last post indicated - 1.475Vdc ("Ok thanks when I unhooked p102 and I read pin 2 and 7 on the ice power module I got -1.475vdc ")
That is what is to be expected: around +5Vdc.
At the module.
Now you need to see what Fender's circuit is doing to that pin.
IF Q9 and C68 are doing there job, when you reinstall P102, that +5 volts at the module should not change.
That is why I asked that you check the Fender side header of P102.

[Jam]

Ok with p102 plugged in to ice module I had +4.75 on pin 2 on the Fender part . Then with p102 unplugged from ice module I get 0Vdc on pin 2 on Fender circuit thanks

[Jazz P Bass]

So the amp is not in mute.

How good are you at tracing signals?

[Jazz P Bass]

A signal inserted into the Input jack should show up at the Send/ Return jacks.
The Send could used to 'send' it to another amp.

You could try putting a signal into the Return jack.
That will bypass the preamp.

The AUX jack will bypass all of the above.
It goes through U7 4 times before it enters the ICE module.
There is a limiter ic on that circuit.
If that is bad it will confuse your readings.

Note: there are excellent test points marked on the schematic that should assist you.

[Jam]

Thanks again I had couple questions on tracing ? I could use about anything for a signal? Then could you use a filter probe or what would work better? any other tips? thanks

[Jazz P Bass]

Anything will work for a signal.

As long as the amplitude is not too large.

You are looking for the signal passing through each IC.
When it stops, you'll know it.

You can use a good volt meter set to read Volts ac.

[Enzo]

Keep your eye on the prize, we are only looking for where the signal stops progressing, so the signal doesn;t matter. it can be distorted or overdriven, it can even just be loud hum. Sometimes I just use a small screwdriver blade. i touch it to a sensitive circuit spot, like an op amp input, and if I hear the resulting hum, I know the stage is amplifying. A signal generator, a CD player, a tape deck, a radio tuner. A guitar works too, but ties up your hands.

[J M Fahey]

Contradicting statements, confirm/discard as approppriate:

Post #9:

on #2 pin of p102 I get -0.540 VDC with headphone plugged in and I get -0.117 VDC with nothing plugged it.

Weird because all voltages should be positive relative to ground.
Expected variation is between +5VDC and 0VDC (or a few mV *positive*)

Post #11:

when I unhooked p102 and I read pin 2 and 7 on the ice power module I got -1.475vdc

Again:
Weird because all voltages should be positive relative to ground.
Expected variation is between +5VDC and 0VDC (or a few mV *positive*)

Post #17:

on the ice power with the p102 unplugged I have+4.75 vdc on pin 2

Well, now that looks normal.

My big gripe with data you are feeding us is that either you canīt measure properly or, say, you write notes down and then read them improperly when quoting them (sloppy handwriting?) :
I am very worried about quoted "-1.475V" and "+4.75V" and I wonder if you are confusing a "+" sign, made out of superimposed horizontal and vertical strokes and "-1" made out of a horizontal stroke with a vertical one just to its right.
Only explanation I find for such diverging values (to boot negative ones are impossible) where the significative part of the number (475) is exactly the same.

On post#20 JPB also notices that, only difference is that I am also trying to find a reason for such values and suspect the first set is wrong, period, and to boot it sent us chasing our tails.

Post #21:

with p102 plugged in to ice module I had +4.75 on pin 2 on the Fender part . Then with p102 unplugged from ice module I get 0Vdc on pin 2 on Fender circuit

Ok, thatīs to be expected. Pin 2 on module is the voltage source,so pin 2 on Fender side follows it.
All Fender can do is to leave it as is or short it to ground through Q9 (if headphones get plugged).

Since you have 5V (+4.75V counts as such) with or without P102 plugged , ICE enable pin seems to work right, so ICE "should" be enabled.

IF so and yet no sound, thereīs basically 2 possibilities:
a) sound is not reaching ICE or:
b) ICE is not reaching speaker.

Crude signal injection:
a) unplug P102 cable
b) check that you still have "+5V" on pin 2 of P102 on ICE module board, relative to pin 6 or 7 which are supposedly Ground.
c) turn amp on/off a couple times, with ear close to speaker, to confirm itīs alive: you hear "something": plop/hiss/buzz/whatever
d) IF alive, grab a small piece of wire, or a resistor leg (1k or less value) and touch P102 pin 8 briefly with its tip: do you hear buzz/tick/click on speaker?
Repeat now touching pin 5 , always on ICE side and nothing plugged in P102.

Please post results.

This is simple "proof of life" test, if positive weīll inject some music.

I could use about anything for a signal? Then could you use a filter probe or what would work better? any other tips?

IF speakers are confirmed good and ICE power starts working on its own, then we consider IT the "signal tracer" and work backwards, eventually reaching the input jack, so we find where signal is lost.

[Jam]

I just wanted to answer Fahey question. Ok I do hear a light hum from speaker and I unplugged p102 and on pin 8 and 5 I got a light buzz from speaker not real loud. I also wanted to post the fan don't work now and the light don't work. I will begin tracing and man these parts are so small on these boards thanks

[J M Fahey]

I just wanted to answer Fahey question. Ok I do hear a light hum from speaker and I unplugged p102 and on pin 8 and 5 I got a light buzz from speaker not real loud. I also wanted to post the fan don't work now and the light don't work. I will begin tracing and man these parts are so small on these boards thanks

I started very worried because a dead fan might mean a dead supply which might mean a dead ICE module, BUT this *weird* amp only turna fan on if ypyou play above a certain volume.
NO thermal detectors of any kind. Weird.

So no fan just mens you are not driving the power amp. So letīs let that aside.

Itīs way more important to confirm that you still have ICE sourced +/-24V available, present on P103.
You might have a slightly different voltage there, say +/- 28V but in any case in the ballpark.

If so (meaning ICE seems to be still alive) get a connector which can plug into ICE P102, a battery powered effects pedal, say a Distortion, a Chorus/Phaser/EQ, or even an active guitar or Bass (or a Piezo equipped Acoustic Guitar, with its own preamp) the idea it must be floating, powered by its own 9V battery, we do NOT want a wall wart or supply here.
The idea being that a fully floating signal generator/souce will *behave* like a *balanced* signal source :O

Just what the Doctor ordered to test this differential/balanced input amplifier :O

So you plug a guitar cable in the Pedal/Guitar output, discard the free plug atbthe other end, separate, twist and tin hot and ground wires, connect ground to P102 pin 5 (P102-5) and Hot to P102 pin 8 (P102-8) .

Do not solder straight to P108 pins, thatīs why I suggested getting ba matching connector.
Worst case, you cut 2 single connectors from an old .1" pitch connector (old PC IDE drive cable or similar) and solder test cable ends there.

Play a couple cords and you should hearvthem through the Rumble speakers; probably not "loud" but definitely "clear".

The idea behind thisn is to check whether ICE works properly and avoid buildingba balanced stage just for this test.

Why didnīt we just use the balanced out from thye Fender preamp

Because itīs still in the list of suspects, weīll test it later.

As I said, my idea is to use the ICE module itself as signal tracer, going backwards step by step.

[Jazz P Bass]

" I also wanted to post the fan don't work now and the light don't work"

Check your power supply.

The fan & the 'ON' LED both run off of the -16 Vdc supply.

Rumble_350_power supply.pdf