Oops Let s Try That One Again Fender

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Kustom trouble

• Thread starter Bodean
• Start date Feb 11, 2017

• #2

Wrong replacement transistor?
BC160...161, BC303...304, 2N3072...73
BFX29 2N2905AKT686G could be used.
Simply at that place must be something broken in the excursion as well the transistors. No transistor breaks without any culprit in the supporting circuit. Check those parts showtime considering a new transistor put in will break also.

All the best,
Robin

• #3

Out of curiosity, how did you check the transistor that seemed bad?
I can't see the schematic, just did y'all utilise an exact replacement, or a substitute?
Sometimes substitutes may have collector/emitter pins reversed from the original.
Was the original a pnp type?

• #iv

A 2n3906 is the needed transistor to supervene upon that first proceeds stage i, but as posted at that place may be a lead difference between the original and the replacements y'all got, yous may also accept other bad Transistors?

Get-go checking the voltages on the schematic with what you accept.
It sounds to me like y'all have D.C. Voltage where it should not be and that's what's kicking your speaker around then much!

• #5

I checked the pinout for both earlier the original and replacement earlier I put it in. They are PNP'southward.
Lile I said earlier the schematic is on the vintagekustom site. Y'all have to get to the site to view it. It cannot be copy/paste or printed. Don't ask me why? The model is a K100C-6, PC1700A or B is the board number, Q1701(2n3638) is the transistor I replaced.
I am a flake of a novice when information technology comes to this. So the schematic shows + and - numbers effectually in various places is that the voltages?

• #6

Yes, the + and - are the voltages to be checked at that bespeak with all controls set like mentioned in the schematics.
Measure out them like mentioned in the schematics and you discover very fast which are wrong considering they are fashion off if the transistor is bad. Or the practical caps or resistors.

All the best,
Robin

• #seven

Yes, the + and - are the voltages to be checked at that point with all controls set up like mentioned in the schematics.
Measure them similar mentioned in the schematics and you discover very fast which are wrong considering they are way off if the transistor is bad. Or the applied caps or resistors.

All the best,
Robin

So should I give voltage measurements for base, collector, and emitter?

• #8

Here are the schematics.

All the best,
Robin

• #9

Then should I give voltage measurements for base of operations, collector, and emitter?

Yes, exactly. Just amp setup like mentioned in the schematics. Power on, all controls full, no signal.
Measure out common ground to voltage point given in the schematics.

• #ten

@Robins
Problem side
E= 12.eight
B= 12.0
C= thirteen.5
Since the other side works I measured the transistor there for comparing but it is the original transistor
E= 0
B= xiv.5
C= sixteen.0
Which isn't what the voltages say on the schematic says for either ane

Last edited: Feb 12, 2017

• #12

?
Do you go +8V reading for the positive rails and -8V reading for the negative rail?
Fresh battery in the multimeter?
Setting of the multimeter?

All the best,
Robin

• #13

?
Do you get +8V reading for the positive runway and -8V reading for the negative rail?
Fresh battery in the multimeter?
Setting of the multimeter?

All the best,
Robin

@Robins
I had it on the wrong setting. Make new meter, and it's opposite of my other one. embarassing

Lets try this
E= two.1
B= six.half dozen
C= vii.3

Good side for comparison
E= 0.9
B=6.9
C= seven.half-dozen

I exercise accept +eight -8 on the rails at present, lol

• #14

@Robins
I had it on the wrong setting. Brand new meter, and it'due south opposite of my other ane. embarassing

Lets try this
E= two.1
B= 6.6
C= 7.iii

Good side for comparison
E= 0.9
B= 6.9
C= 7.six

I do have +8 -viii on the rails at present, lol

No problem, I have been through that several times even measuring with a weak battery. A lot of multimeters aren´t expert enough for those kind of measurings anyway.
Allow´southward see what nosotros have.

I am certain you exchanged E and C on the transistor, let´s presume the readings are:
Eastward= seven.3 (pointer side transistor, positive rails voltage)
B= 6.six
C= -ii.1 (there´southward the cap)

Practiced side for comparison
Eastward= 7.half-dozen (arrow side transistor, positive rail voltage)
B= vi.9
C= -0.9 (there´due south the cap)

Emitter is the supply side of the transistor (where the arrow is) considering Q1701 is a PNP transistor.
B and E are adept on the new one.
The C is too high and I would modify the cap C1705(applied betwixt B and C) for a first bank check. Transistor is good and working.

All the best,
Robin

Terminal edited: Feb 13, 2017

• #15

No trouble, I accept been through that several times even measuring with a weak battery. A lot of multimeters aren´t good plenty for those kind of measurings anyway.
Permit´s see what nosotros take.

I am sure you exchanged E and C on the transistor, let´south assume the readings are:
East= 7.iii (arrow side transistor, positive rail voltage)
B= 6.6
C= -2.1 (at that place´due south the cap)

Adept side for comparison
E= 7.6 (arrow side transistor, positive rails voltage)
B= half dozen.9
C= -0.9 (there´due south the cap)

Emitter is the supply side of the transistor (where the arrow is) because Q1701 is a PNP transistor.
B and East are good on the new one.
The C is too loftier and I would alter the cap C1705(applied between B and C) for a beginning check. Transistor is adept and working.

All the best,
Robin

Thank you for your help as always @Robins. That cap I volition accept to find if I need to use a tantalum. I have a 100uf 16v electrolytic on hand.

Last edited: Feb 13, 2017

• #16

Transistor 1701 is non the first gain stage transistor, is 1700 and 1701 both bad?

I have never had ane of those types of caps ( c1705) become bad in a depression voltage amp like this, but annihilation is possible and it's easy enough to pull it and check it.

95% of the time it's a leaky to totally shorted electrolytic that is bad.

Did you have a hard time getting any of the nuts off the pots shaft to dorsum the lath off the chassis?
At times I have had to utilise enough force to do such that I bankrupt the plastic resistive carbon trace on the pot which fabricated it go a open circuit!
If that lath was worked on before this may have taken place?

You can elevator one cease of c1705 and tack in place that 100uf cap that you take only to meet if that's the problem as you will not hurt anything.

Concluding edited: Feb thirteen, 2017

• #17

Transistor 1701 is non the first gain phase transistor, is 1700 and 1701 both bad?

I accept never had one of those types of caps ( c1705) go bad in a depression voltage amp like this, simply annihilation is possible and it's piece of cake enough to pull information technology and cheque it.

95% of the time it's a leaky to totally shorted electrolytic that is bad.

Did you take a hard time getting whatsoever of the basics off the pots shaft to back the board off the chassis?
At times I have had to use enough force to do such that I broke the plastic resistive carbon trace on the pot which made it go a open up excursion!
If that board was worked on earlier this may have taken place?

You can lift one finish of c1705 and tack in place that 100uf cap that you have just to come across if that'southward the trouble equally you lot volition non hurt anything.

No sir, there was not any problem with getting anything off. I was real careful removing the board. I checked the volume pot connections on the back of the lath and compared them to the to the working side. They were close if I retrieve right.
I volition effort the capacitor I accept to see what information technology does.

• #18

Dude, Robins like that guy you call when you have a trouble with your car and you dont know jack about cars lol

• #19

Transistor 1701 is non the first proceeds phase transistor, is 1700 and 1701 both bad?

I take never had one of those types of caps ( c1705) go bad in a low voltage amp like this, but anything is possible and it'due south easy enough to pull it and bank check it.

95% of the time it'due south a leaky to totally shorted electrolytic that is bad.

Did you lot accept a hard time getting whatever of the nuts off the pots shaft to back the board off the chassis?
At times I have had to use enough forcefulness to practise such that I broke the plastic resistive carbon trace on the pot which made it become a open up circuit!
If that board was worked on before this may have taken place?

You tin elevator i end of c1705 and tack in place that 100uf cap that y'all have just to encounter if that'due south the problem equally you will not hurt anything.

I had a bad "treble " pot on an amp once.
Information technology was physically broken on the inside, and was an open in the ckt.

Took me a scrap to figure it out, as I was able to trace the signal, it stopped dead at the treble command.

It had apparently taken a knock in transit, but didn't show any harm that I was able to run across from the outside.

I figure the shaft got pushed in and broke the carbon trace.

That was a frustrating repair until I found the problem.

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Source: https://www.strat-talk.com/threads/kustom-problem.427146/

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