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Author Topic: Polytone Taurus Elite amp low volume no schematic!  (Read 21879 times)

Roly

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Re: Polytone Taurus Elite amp low volume no schematic!
« Reply #45 on: September 22, 2013, 01:16:54 PM »
Quote from: DrGonz78
Are any opamps getting hot in conjunction with the regulator getting hot?

Yup, or, paradoxically, do any of the op-amps seem to be stone cold while the others are just warm?  Both hot and cold conditions are suspect.
If you say theory and practice don't agree you haven't applied enough theory.

EDWARDEFFECT1

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Re: Polytone Taurus Elite amp low volume no schematic!
« Reply #46 on: September 22, 2013, 02:20:31 PM »
the -15v regulator is slightly warm and at proper voltage.the +15v reads .003vdc and gets hot to the touch.going to do a pinkie test on the op amps as dr gonz metioned and see what i get.i removed 2 op amps from the reverb board as there was a capacitor arcing due to a bad solder joint.thought that an op amp might of got fried ,so i removed them from circuit and it had no effect on the regulator voltage...off to the pinkie test. was outside fixing a broken brake line and bleeding brakes. back to the amp....ed
« Last Edit: September 23, 2013, 09:09:49 AM by EDWARDEFFECT1 »

Roly

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Re: Polytone Taurus Elite amp low volume no schematic!
« Reply #47 on: September 23, 2013, 11:01:01 PM »
Quote from: EDWARDEFFECT1
the +15v reads .003vdc and gets hot

So it's a pretty fair bet that there is a short somewhere on the +15V rail.  The current path can sometimes be found by very careful low voltage measurements - a shorted chip will be the one with the least voltage across it (or its supply to its local ground).


I've been asked to explain why a defective IC or semiconductor might be cold.

Mostly when a semiconductor fails it still has some resistance, sometimes quite a bit of resistance, and as it draws current from whatever supply it dissipates power, P = I2R, and gets warm or hot, giving rise to the "burnt finger test".

It is also possible that it could fail open circuit, say due to excessive current burning out the fine interconnects between the external leads and the chip like tiny fuses.  No current, no heat.

The other failure mode can occur when the chip suffers a catastrophic failure and melts down into a conductive blob.  This can happen when mains voltage gets to low voltage circuits and IC's get a blast of current in reverse, where the bulk chip substrate gets forward biased, and the whole complex IC looks like a very simple forward biased diode, passes massive current, and simply melts.  In this case the result may be a chip that has only a few ohms of resistance, and we have the opposite case, current, but no resistance worth talking about to generate heat.

Power, thus heat, can only be dissipated in a resistance.  Both open circuits, and dead short circuits, have no resistance, thus generate no heat ('tho a short may well generate a lot of heat in the power supply).

As always you should suspect the odd one out, a chip that is hotter, or colder, than the others around it.

HTH
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

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Re: Polytone Taurus Elite amp low volume no schematic!
« Reply #48 on: September 24, 2013, 01:38:47 AM »
Solving that kind of problem is pesky because "1 shorted part makes *all other* parts connected in parallel with it alsi look/measure shorted"
which in practice means that if you have, say, 15 IC's fed from same pair of rails, you'll have to pull them all, one by one, until the short disappears .... ugh !!!

*But* in this amp, thanks God you have 4 or 5 PCBs interconnected by physical wires, so follow the path from +/-15V source until the furthest IC and lift wire pairs in due sequence, until +/-15V reappears at the PSU, then you'll have to pull only a hadful of ICs.

And if removing the full Preamp still shows lack of +15V, then the short is in the cap immediately following it or in the connector, if any.

EDWARDEFFECT1

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Re: Polytone Taurus Elite amp low volume no schematic!
« Reply #49 on: September 25, 2013, 02:45:47 PM »
i pulled all the ic's and still no +15v.all were in sockets thank god!i found a solder bridge between a black ground wire and the positve of the circuit. it has been corrected.the big short is gone,but apparently i still have one to find. i found 2 capacitors with bad solder joints and fixed them with buss wire as i think the trace was loose or missing(coudln't solder,so i followed the trace to the next component and buss wired the lead to the next component).all fixed now!i took the preamp board outside to get really good look in  natural light and looked it over with a fine tooth comb.i found a solder bridge on the one board and opened it up hoping that was my short to no avail.when i turn the unit on the +15v reads 11vdc then diminishes to 3vdc.still something drawing voltage from my supply.when turning the amp on there is a loud squeal.when we hooked a guitar to the input it had a loud guitar sound and squeal for about 4 seconds then nothing no squeal due to lowered voltage.....ed
« Last Edit: September 25, 2013, 05:37:14 PM by EDWARDEFFECT1 »

J M Fahey

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Re: Polytone Taurus Elite amp low volume no schematic!
« Reply #50 on: October 02, 2013, 09:37:53 PM »
Sorry but now it's in your hands, only you can physically look at it under good light and a loupe.
Anyway, if pulling all IC didn't solve it, then start from the o0ther end: disconnect the +/_ 15V supply from *any* load and check whether you recover normal voltage.
If not,check the supply itself.
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