Marshall VS100 blowing fuses

brokenbones · 05-07-2008, 05:04 AM

My amp had a blown fuse. I go to the hardware store to replace the blown fuse with a new one. Come to find out that the blown fuse is a 250v fuse while on the amp it says "230v or 150v". Did the previous tech "hotwire" this amp? So I bought a new 250v fuse and and the amp immediately blows the fuse. Everything I've read so far suggests its either the tube or valve. Does this sound correct? Or, should I find a 230v and try that? Any suggestions? -Eric

Enzo · 05-07-2008, 05:53 AM

If printed on the amp you see something like 120v 4A and 240v 2A, that means when the amp is running on 120 volts as in the USA, the main fuse is a 4 amp, and when running on 240 volts as in Europe and elsewhere the fuse is 2 amps.

The voltage printed on the fuse is not the issue. If you need a 4 amp fuse, then most any 4 amp fuse will be fine. Just be aware there are regular faast blowing fuses and slow blowing fuses, also called timed or time delay fuses. But you MUST use the proper AMP rating fuse. Forget the fuse voltage. The vvoltage printed on the amp is for the amp.

Nobody likely "hotwired" anything. The fact the fuses blow means they are not bypassed.

It is real unlikely the tube is blowing the main fuse.

Much more likely you have a blown output stage, meaning shorted output transistors.

brokenbones · 05-08-2008, 12:00 AM

I hooked my Multimeter up to all three of the transistors and tested them. On two of the output transistors, two of the three "arms" had a 0 rating. The other transistor had one bad "arm". I'm guessing these need replaced? Is there anything else that should be tested/replaced? How hard is it to replace the transisitors?

Enzo · 05-08-2008, 05:40 AM

Not sure what you mean "one bad arm."

DOn't measure resistance to ground, measure resistance between the legs. If two legs measure zero ohms between them, then that transistor is probably shorted.

I don't find it hard to replace transistors, but then I do it for a living. it is a matter of unsoldering and removing the old and soldering the new in its place.

rockintothebone · 03-26-2009, 10:54 PM

even i got that problem but ..is there anyway to figure the problem without unsoldering anything?

Enzo · 03-26-2009, 11:38 PM

Well no, not really. There are no socketed parts to speak of in there. Fuses you can replace, but until you find and repair the reason they are blowing, they will continue to do so. ANy repairs to be made will require soldering of parts.

rockintothebone · 03-27-2009, 01:09 AM

thanks for replyin mate...
i realise i have to solder to repair it
but how exactly do i find the problem first?
are there any steps to follow ?
(for example check the resistance between two points of the circuit)

Enzo · 03-27-2009, 01:37 AM

Well, if you are blowing fuses, then I would start by checking the power transistors. See if any two legs are shorted together.

rockintothebone · 03-27-2009, 01:43 AM

i tried checkin the resistance.. two legs of the t9 and t10 showed 4ohms

ill link you to the schematics .

http://www.drtube.com/schematics/mar...v100-62-02.pdf

rockintothebone · 03-27-2009, 02:17 AM

heres the picture of the circuit

Enzo · 03-27-2009, 05:20 AM

REmove them and check them off the board. It appears they are shorted.

Are they the BDV65s? Or are they TIP142/147?

rockintothebone · 03-27-2009, 04:31 PM

according to the schematics it says t9 and t10 are bdv65
and t11 & t12 is bdv64
i wonder ill unsolder them and let you know

Enzo · 03-28-2009, 02:05 AM

If you need to replace the BDVs, you can use the TIP142/TIP147 pair of transistors. Make sure to get the same package type.

rockintothebone · 03-28-2009, 06:55 PM

i managed to desolder t12... its a marshall t64 ...st microelectronics tip147..

now t11 has higher resistance...but th t9 and t10 still have low resistance between the legs

rockintothebone · 03-28-2009, 11:16 PM

I managed to remove t10 and t12

so now the t10(Marshall T65) and t12(Marshall T64)(ST Tip147)

the T64 has a low resistance of 0.06 ohms between the collecter and emitter
and
the T65 has a low resistance of 3.4 ohms between the collector and emitter

i connected the circuit back without these two transistors and the fuse didnt blow...

now..
can i replace these two faulty transistors with ANY TIP142 and TIP147 ..or shud i get certain ones?

Enzo · 03-30-2009, 08:16 PM

Look at the shape of your BDV part. You want a TIP part of the same shape - what we call its package.

TO - for Transistor Outline - is the shape designation. TO-220 is a smaller version. TO218 is a larger tab top type. TO248 is a large rectangular type. Then there is TO3P. The TIP142/147 parts come in all those packages.

I think your BDVs are either TO3P or TO218. Both are about the same size. One has the screw hole through the tab only, while the other has the body extended up farther with the screw hole through it.

ANd remember to keep track of which part replaces which. Don;t mix up the NPN and PNP parts.

rockintothebone · 04-01-2009, 04:07 PM

i replaced t10 and t12
the amp worked fine for a few minutes and blew the fuse again
now when i checked the power transistors
the t11s short..

how can this happen ?

52 Bill · 04-01-2009, 09:09 PM

Quote:

Originally Posted by rockintothebone

the t11s short..how can this happen ?

If you replaced some of the original outputs with the TIP parts and left in some of the old parts, you set up a mis-match where the device at T11 had to work harder than the new part.

Try replacing all of the outputs with one type or the other.

Be sure to check the rest of the circuit (drivers, resistors, bias diodes, etc.) for problems as well.

rockintothebone · 04-30-2009, 12:35 AM

after a lot of hassle... finding all four transistors in the right package ... i replaced all the four (the body extended up farther with the screw hole through it)......as soon as i switched it on.... the t11 was short and the t10 had low resistance(30 ohmns) between two legs...

i desoldered the t11 and t10... but ..when i hook up my multimeter(20 k) the resistance continues to increase slowly... could this be a faulty capacitor ?

52 Bill · 04-30-2009, 06:32 PM

Quote:

Originally Posted by rockintothebone

after a lot of hassle... finding all four transistors in the right package ... i replaced all the four (the body extended up farther with the screw hole through it)......as soon as i switched it on.... the t11 was short and the t10 had low resistance(30 ohmns) between two legs...

Did you check the rest of the circuit as well? Sometimes more than just the outputs will short when the circuit dies, and if you don't catch those problems then they will cause the new outputs to die again.

I would check all of the transistors and diodes in the power amp. Are you powering up the amp with a speaker connected? For now, don't. Do you have a light bulb limiter or a variac? Did you re-install the insulator washers on the output transistors when you replaced them? Did you use heatsink grease on the new outputs?

Quote:

Originally Posted by rockintothebone

i desoldered the t11 and t10... but ..when i hook up my multimeter(20 k) the resistance continues to increase slowly... could this be a faulty capacitor ?

What are you hooking the meter to, the circuit or the transistors? If you put your meter on the board, you could be charging up a filter cap with the meter battery. This is why you get the rising resistance measurment.

rockintothebone · 05-02-2009, 01:50 AM

im not connecting the speaker ...i dont have a light bulb limiter or a variac...the previous transistor had no insulator washers ...and i didnt use heatsnk grease because there is still some left on the heatsink...

i kept hooking my multimeter to the circuit with the faulty transistors removed..

while i was checking the circuit i found something weird R16 , R17, R18 ,R20, R22 ,R23 each having a value of more than 100 ohms somehow had a resistance below 50 ohms..i desoldered R18 cause it had the lowest ohm rating than the rest and checked its resistance ...it showed 100 ohms.....it cud be minute mistake.. but how is it possible ...?

heres the schematics ...
http://www.drtube.com/schematics/mar...v100-62-02.pdf

thanks

Enzo · 05-02-2009, 02:07 AM

Because while soldered into the circuit, those resistors are essentially in parallel with each other, so the apparent value reads low.

rockintothebone · 05-03-2009, 01:15 PM

well i did check all the diodes and transistors they all seem pretty ok ..what sthe next step i need to follow.. i dont know any other way to check capacitors other than to look for leakage or buldging...and none of them are...
plz help

05-07-2008, 05:04 AM	#1
brokenbones Junior Member Join Date: May 2008 Posts: 2	Marshall VS100 blowing fuses My amp had a blown fuse. I go to the hardware store to replace the blown fuse with a new one. Come to find out that the blown fuse is a 250v fuse while on the amp it says "230v or 150v". Did the previous tech "hotwire" this amp? So I bought a new 250v fuse and and the amp immediately blows the fuse. Everything I've read so far suggests its either the tube or valve. Does this sound correct? Or, should I find a 230v and try that? Any suggestions? -Eric

03-26-2009, 11:38 PM	#6
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	Well no, not really. There are no socketed parts to speak of in there. Fuses you can replace, but until you find and repair the reason they are blowing, they will continue to do so. ANy repairs to be made will require soldering of parts. __________________ Education is what you're left with after you have forgotten what you have learned.

03-27-2009, 01:37 AM	#8
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	Well, if you are blowing fuses, then I would start by checking the power transistors. See if any two legs are shorted together. __________________ Education is what you're left with after you have forgotten what you have learned.

03-27-2009, 01:43 AM	#9
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	i tried checkin the resistance.. two legs of the t9 and t10 showed 4ohms ill link you to the schematics . http://www.drtube.com/schematics/mar...v100-62-02.pdf Last edited by rockintothebone; 03-27-2009 at 01:45 AM. Reason: added link

03-27-2009, 05:20 AM	#11
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	REmove them and check them off the board. It appears they are shorted. Are they the BDV65s? Or are they TIP142/147? __________________ Education is what you're left with after you have forgotten what you have learned.

05-07-2008, 05:53 AM	#2
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	If printed on the amp you see something like 120v 4A and 240v 2A, that means when the amp is running on 120 volts as in the USA, the main fuse is a 4 amp, and when running on 240 volts as in Europe and elsewhere the fuse is 2 amps. The voltage printed on the fuse is not the issue. If you need a 4 amp fuse, then most any 4 amp fuse will be fine. Just be aware there are regular faast blowing fuses and slow blowing fuses, also called timed or time delay fuses. But you MUST use the proper AMP rating fuse. Forget the fuse voltage. The vvoltage printed on the amp is for the amp. Nobody likely "hotwired" anything. The fact the fuses blow means they are not bypassed. It is real unlikely the tube is blowing the main fuse. Much more likely you have a blown output stage, meaning shorted output transistors.

05-08-2008, 12:00 AM	#3
brokenbones Junior Member Join Date: May 2008 Posts: 2	I hooked my Multimeter up to all three of the transistors and tested them. On two of the output transistors, two of the three "arms" had a 0 rating. The other transistor had one bad "arm". I'm guessing these need replaced? Is there anything else that should be tested/replaced? How hard is it to replace the transisitors?

05-08-2008, 05:40 AM	#4
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	Not sure what you mean "one bad arm." DOn't measure resistance to ground, measure resistance between the legs. If two legs measure zero ohms between them, then that transistor is probably shorted. I don't find it hard to replace transistors, but then I do it for a living. it is a matter of unsoldering and removing the old and soldering the new in its place.

03-26-2009, 10:54 PM	#5
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	even i got that problem but ..is there anyway to figure the problem without unsoldering anything?

03-27-2009, 01:09 AM	#7
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	thanks for replyin mate... i realise i have to solder to repair it but how exactly do i find the problem first? are there any steps to follow ? (for example check the resistance between two points of the circuit)

03-27-2009, 04:31 PM	#12
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	according to the schematics it says t9 and t10 are bdv65 and t11 & t12 is bdv64 i wonder ill unsolder them and let you know

03-28-2009, 02:05 AM	#13
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	If you need to replace the BDVs, you can use the TIP142/TIP147 pair of transistors. Make sure to get the same package type. __________________ Education is what you're left with after you have forgotten what you have learned.

03-28-2009, 06:55 PM	#14
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	i managed to desolder t12... its a marshall t64 ...st microelectronics tip147.. now t11 has higher resistance...but th t9 and t10 still have low resistance between the legs Last edited by rockintothebone; 03-28-2009 at 07:48 PM.

03-28-2009, 11:16 PM	#15
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	I managed to remove t10 and t12 so now the t10(Marshall T65) and t12(Marshall T64)(ST Tip147) the T64 has a low resistance of 0.06 ohms between the collecter and emitter and the T65 has a low resistance of 3.4 ohms between the collector and emitter i connected the circuit back without these two transistors and the fuse didnt blow... now.. can i replace these two faulty transistors with ANY TIP142 and TIP147 ..or shud i get certain ones?

03-30-2009, 08:16 PM	#16
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	Look at the shape of your BDV part. You want a TIP part of the same shape - what we call its package. TO - for Transistor Outline - is the shape designation. TO-220 is a smaller version. TO218 is a larger tab top type. TO248 is a large rectangular type. Then there is TO3P. The TIP142/147 parts come in all those packages. I think your BDVs are either TO3P or TO218. Both are about the same size. One has the screw hole through the tab only, while the other has the body extended up farther with the screw hole through it. ANd remember to keep track of which part replaces which. Don;t mix up the NPN and PNP parts. __________________ Education is what you're left with after you have forgotten what you have learned.

04-01-2009, 04:07 PM	#17
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	i replaced t10 and t12 the amp worked fine for a few minutes and blew the fuse again now when i checked the power transistors the t11s short.. how can this happen ?

04-30-2009, 12:35 AM	#19
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	after a lot of hassle... finding all four transistors in the right package ... i replaced all the four (the body extended up farther with the screw hole through it)......as soon as i switched it on.... the t11 was short and the t10 had low resistance(30 ohmns) between two legs... i desoldered the t11 and t10... but ..when i hook up my multimeter(20 k) the resistance continues to increase slowly... could this be a faulty capacitor ?

05-02-2009, 01:50 AM	#21
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	im not connecting the speaker ...i dont have a light bulb limiter or a variac...the previous transistor had no insulator washers ...and i didnt use heatsnk grease because there is still some left on the heatsink... i kept hooking my multimeter to the circuit with the faulty transistors removed.. while i was checking the circuit i found something weird R16 , R17, R18 ,R20, R22 ,R23 each having a value of more than 100 ohms somehow had a resistance below 50 ohms..i desoldered R18 cause it had the lowest ohm rating than the rest and checked its resistance ...it showed 100 ohms.....it cud be minute mistake.. but how is it possible ...? heres the schematics ... http://www.drtube.com/schematics/mar...v100-62-02.pdf thanks Last edited by rockintothebone; 05-02-2009 at 01:53 AM. Reason: added schematics link

05-02-2009, 02:07 AM	#22
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,281	Because while soldered into the circuit, those resistors are essentially in parallel with each other, so the apparent value reads low. __________________ Education is what you're left with after you have forgotten what you have learned.

05-03-2009, 01:15 PM	#23
rockintothebone Junior Member Join Date: Mar 2009 Posts: 11	well i did check all the diodes and transistors they all seem pretty ok ..what sthe next step i need to follow.. i dont know any other way to check capacitors other than to look for leakage or buldging...and none of them are... plz help

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