Question about Marshall Mg15dfx 15-Watt Combo Guitar Amplifier

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No output, have checked through to transistors fitted to heatsink but can't read what type they are so that I can check them

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  • Marshall Master
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The 30 Watt version uses MJ3001 (NPN) and a MJ2501 (PNP) in a standard emitter follwer arrangement. TR4 looks like a BC184 but drawing is not too clear and this transistor is CRITICAL as it sets the bias for the two output transistors, and if it fails, the outputs will fry.

Here is typical schematic:

http://elektrotanya.com/marshall_30w_5203.pdf/download.html

Since you are not a registered user of the site, scroll down hte page and nearer the bottom is a small link that says "Get Manual" to click on to start download. The is a statement next to it that as unregistered you are only allowed two downloads a day.

Posted on Mar 19, 2011

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Posted on Jan 02, 2017

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2 Answers

My Peavy XR800F just had all its pots replaced and now iam getting very low output.. any ideas please ?


Output transistors or the preceding driver stages may be failing. Check for electrolytic capacitors for bulging tops, they will have to be replaced.

Sep 09, 2016 | Ideas Music

Tip

A) basically it has to be acted upon by a supply voltage of at least 95V to...


a) basically it has to be acted upon by a supply voltage of at least 95V

to work.

sample picture

f3f741f.jpg







b) of course, assuming the horizontal deflection oscillator works, same

with the horizontal drive and horizontal output transistor

58689de.jpg






it would generate output voltages on the secondary terminals

and 200V line will be active sending voltages to the

Video Drive circuits. Of course high voltage will be generated

ranging to at least 30 KV and there will be voltages on the G2 of the tube.


c) the easiest test point to look when it is oscillating, is the CRT heater

voltage, the heater lit when flyback is good ( mostly at night times when it

is dark ) and you can hear sounds, too.

here is a sample image

ab6c901.jpg



marked with letter H and H1

Green Arrow for the G2 voltage


d) having a B+ voltage reading of 75 V or lesser ( primary pins )

indicates a bad or partially shorted flyback, assuming your

horizontal output transistor and power supply are good & OK.

sample of H out

b3363d6.jpg


These only applies to CRT type TV's.

on Dec 24, 2009 | Music

1 Answer

Everything comes on lights can see the music is playing no sound


a fuse gone to the speaker terminal of the end amplifier.
There are four lots steering and power transistors or only an integrated powerpack ic to find possible IC in one or in 2 pieces .... can be defective. final stage amplifier is almost always to find on a large heatsink or the cabinet with transistors, or MOSFETs or a one large STK ic they are almost always short-circuited if defect and it is easy to find if defective with a multimeter as it are conventional vintage simple NPN and PNP transistors, it may be that if you have a multimeter ohm sets and measurement performed no resistance is given on the three legs ie the shorted than you the transistors mosfets or sometimes replace an IC output stage 1 or 2 pieces, but do not forget or bad bulging capacitors are responsible or that there was an overload or shorting a speaker cable that has become trapped in the door or a cabinet.
Much options to suggest in case of no sound or only loose connection by shifting a carpet

Mar 23, 2016 | Music

2 Answers

Why does amplifier sound die after a short period of use?


There is a heat sensor on the heatsink (to cooling IC / transistor) which decides current / voltage, in case of overheating. This is indeed to secure IC / transistor power of destruction.
The cause of the excessive heat, the impedance mismatch between the amp to the speakers. It is also possible that parts already exist within the amplifier that is almost / half broken, for example, changing the resistor value, electrolytic capacitors are bulging or dried, isolation transformer windings were charred, solder joint cracking etc. Should be checked, before the fatal damage.

Heatsink on the amplifier (the picture is owned Connelectronic):


25850288-l1qpqmriditabltrjczr2eku-4-0.jpg

Sep 05, 2015 | Laney Music

2 Answers

Why does fuse blow when unit is powered up


I rather suspect IC1 TDA7293 is the cause of your problem. If this is the case you will need to check the speaker/s

Nov 12, 2014 | Marshall Amplification Marshall MG250DFX...

1 Answer

I am no longer able to turn on my amp. I was running a bass head through it a few months ago, and havent used it since. Now the amp wont turn on at all. I have tried turning the master volume down to 0,...


probolly all you did was run a head into another amp and just caused your marshall to overheat/overpower and blew your output transistor. i you drop the chassis out and look at the chip on the heatsink is it blown? also check all internal and external fuses.

Nov 24, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

I have a beringer 5000 mixer and can not get no sound from it. it's like the speakers are not getting power


Oh, oh... got one on the bench now... There is a design defect that causes a short and destruction in the power amp portion.

Do a test: Plug headphones into the main 1/4 inch jacks. The sound won;t be very loud since these are line outputs, not for headphones.

IF you get sound out those, then one or both power amps are dead.

Worst case: if one amp is dead, several parts including three power MOSFET transistors are fried for any of the dead channels.
The failure of the amp can wipe out the main power supply. If you effect windows light up, then the small power supply is operating.
If the big supply is fried, there are two large MOSFET switching transistors that are gone. Often several smaller transistors and dides and resistors and one switching IC goes. MOST of these are surface mounted parts and would be beyond the scope of what you can repair.

I am trying to contact Behringer about the flaw but haven't heard back yet.

The nature of the flaw is this: The is insufficient clearance on an internal circuit layer from the edge that fits into a slot in the power amp heatsink. Any humidity that enters can cause the insulation to breakdown and arc to the heatsink causing a chain reaction.
I repaired one of these already before finding the cause, but this one had a smoking gun! I just yesterday milled out the slot deeper and wider and will put insulating tape to prevent further arcing. The arcing that had occured burned away the internal layer and the connections. I will replace thoose with hardwire.

Repair of this problem is time consuming to weed out all the blown parts and to safely bring the unit back to life.

The current unit I am working on took out ONLY the power amp. A 30 milliohm resistor went up in smoke making a real mess. All three power MOSFETS are gonzo and a zener as well... don't know what else I will find. The previous unit was worse as the power supply was wiped as well.

Feb 06, 2010 | Behringer Pmp3000 16 Channel Audio Mixer

1 Answer

Got a 5000 euro power the output module has gone i think as it turns of after 2 seconds can you get a replacement part copy


I had to repair mine. An arc had occured between circuit traces and a heatsink in the power amp and that took out a half dozen transistors, a switching regulator chip, two power resistors, diodes. The parts are all available BUT you must be very careful to weed out ALL the bad ones.

AFTER repair, put a 150 wat light bulb in series when powering up to avoid damage IF there still is a bad component in the circuit.

After cutting out the damaged board and replacing the parts it is all working again.

I had to trace out some of the circuit to troubleshoot as Behringer won't give out schematics.

The amplifier in this is a class "D" switching type. Be very careful of running the unit if the speakers are not connected.

Nov 04, 2009 | Behringer Pmp3000 16 Channel Audio Mixer

2 Answers

Wurlitzer 200a electric piano replacement transistors


do you have the numbers off the transistors? i can look up the data sheets and pick a suitable or improved replacement.

Jan 12, 2009 | Music

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