TSL100 Blowing Mains Fuses

[fractalsoup]

Hi, I have TSL100. Keeps blowing mains fuse when switching on. Have tested all valves in a tester and no shorts. Even without power tubes in mains fuse still blows. (In UK so T2A).


Looking for guidance on how to test if the mains transformer has gone bad. Have multimeter but dont have a variac. Do have a 30V power supply for basic hobby electronics though so in theory could test for voltage in circuits.

If PT ok then thinking input board (rev 3) has bad film caps.

On mainboard the 2 main capacitors 330uF @ 315V look bulging on top. Would they blow a mains fuse if bad?

Thanks

 

[Rodical]

Mine has done same 3x in 20 years... I found a good tech... Beleave he mentioned power tubes bad... Then he checked solder connections... Thats all I got...

 

[Dogs of Doom]

to the forum...

what year is the amp?
which ISS# is the main board?

how does capacitor C-49 look?

also to look at are resistors R-6 & R-9

 

[fractalsoup]

Year of Amp is 2001 Mainboard Rev 5

Couldn't find c-49 but c-46 is ok
R6 an R9 both ok

Thanks also re power tubes - have tested them all in a tester and no shorts, etc Mains fuse blows without power tubes installed as well

 

[Dogs of Doom]

Year of Amp is 2001 Mainboard Rev 5

Couldn't find c-49 but c-46 is ok
R6 an R9 both ok

Thanks also re power tubes - have tested them all in a tester and no shorts, etc Mains fuse blows without power tubes installed as well

sorry, I meant C-46... dyslexic typo...

how proficient are you w/ electronics & safety?

There are some tests, that you can do w/ a multimeter, but, most of them require having high voltage on & testing...

what speaker out are you using? 16 ohm, or 4/8 ohm?

 

[Gunner64]

If the main fuse blows as soon as he powers on, with tubes in and tubes out how is he going to check voltages in the amp?

 

[anitoli]

If the 330uf caps were that bad they would have prolly expolded already. Fuse F1 should be a T4A type fuse. This is a slow blow fuse. Make sure you aren't using a fast blow as the inrush current at startup may kill a fast blow by default.

 

[6StringMoFo]

That happened to me but you're not going to like the fix.

My PT blew up. Needed to replace it.

GL mate.

 

[Tatzmann]

Put appropriate fuse in. Disconnect all secondaries from the powertransformer. If it still fuses then it's either the transformer itself or the mainsswitch.

If it doesn't fuse you'll have to look at the heaterwiring, rectifiers, caps, for shorts and so on.

Powertransformers in such amps can pull up to about 30Amps for a couple of milliseconds at powerup. I have an early Laney GH100 that blew the mainsfuse repeatedly without anything beeing bad. After I put an appropriate NTC in the mains it never blew again. At later years the GH amps came stock with such an NTC.

 

[fractalsoup]

Put appropriate fuse in. Disconnect all secondaries from the powertransformer. If it still fuses then it's either the transformer itself or the mainsswitch.

If it doesn't fuse you'll have to look at the heaterwiring, rectifiers, caps, for shorts and so on.

Powertransformers in such amps can pull up to about 30Amps for a couple of milliseconds at powerup. I have an early Laney GH100 that blew the mainsfuse repeatedly without anything beeing bad. After I put an appropriate NTC in the mains it never blew again. At later years the GH amps came stock with such an NTC.

Thanks for all the info. With all secondaries disconnected it still blows mains fuse so am starting to think transformer is shorted. I get no continuity between sides but on primary there is continuity between each of the poles in any combination.

Mains switch has continuity as expected when switched on and none when off.

The two film caps on the power cable board are for the HT circuit is that correct so nothing to do with PT primary.

 

[fractalsoup]

The capacitor at C1 has continuity between the poles with no power. Does this mean its shorted open and likely to be the problem? Thanks.

C1 is a grey coloured Class X 47n 250 V safety capacitor.

If it has failed does anyone know where I can source one in the UK?

 

[fractalsoup]

I desoldered the so called “death cap” C1 and tried power with fuse in and it tripped the house breaker. So I am guessing there is a short in the power transformer. I still had the secondaries disconnected.
It did not blow the amp fuse however. So my other thought is that the power transformer is ok but because the safety cap was missing it just sent too much voltage back up the line.

What is the correct way to test the transformer?
Thanks

 

[anitoli]

The capacitor at C1 has continuity between the poles with no power. Does this mean its shorted open and likely to be the problem? Thanks.

C1 is a grey coloured Class X 47n 250 V safety capacitor.

If it has failed does anyone know where I can source one in the UK?

C1 is on one side of a loop. There will be continuity if it's there or not if the transformer is hooked up.

 

[6StringMoFo]

I'd test the continuity of the coils in your PT (power transformer) with the leads disconnected.

Someone will chime in with safety precautions.

(I have never discharged an amp) (YES I Know!)

 

[Gunner64]

I thought it still blew fuses with the secondaries disconnected? Powertrans or switch/wiring itself right?

 

[fractalsoup]

I thought it still blew fuses with the secondaries disconnected? Powertrans or switch/wiring itself right?

That is correct. Need guidance on testing power transformer safely.

 

[Gunner64]

You can't apply power without blowing the fuse. Doesn't get any safer than that.

If what you're telling us is true
You pretty much diagnosed it.

If the switch and primary wiring isn't shorted, and it blows the MAINS fuse with the secondaries disconnected there's only 1 culprit left.

 

[PelliX]

I thought it still blew fuses with the secondaries disconnected? Powertrans or switch/wiring itself right?

This. Without secondaries the caps are irrelevant (even though bulging caps are almost always a sign of partial or compelte failure).

I'd test the continuity of the coils in your PT (power transformer) with the leads disconnected.

Assuming the secondaries are disconnected, no need to worry about draining caps unless you wander off into other areas of the amp.

Check the DC resistance of the live and neutral prongs of the plug (UK, so the shorter ones) with the power switch in the ON position (disconnected from mains, of course). Post that value.

Then measure the DC resistance of the secondaries (again, amp still disconnected from mains). Note that the secondaries must still be disconnected from the rest of the circuit. Post those values.

Note that this is not a conclusive test, your multimeter will put a few volts across the transformer to test the resistance, while transformers can develop faults that only become apparent at higher voltages. It's generally a pretty good indication, though.

I desoldered the so called “death cap” C1 and tried power with fuse in and it tripped the house breaker

C1 isn't actually what's generally referred to as a death cap as it's referencing the negative of the DC from the rectifier to chassis (mains) earth. Death caps are or were called death caps because they're located straight between the AC mains in (phase or neutral, depending on how your socket is wired, how you plug it in if not using a polarized plug, how it was designed and sometimes on the position of a switch) and thus could potentially, under the right circumstances, put the chassis at wall AC voltage potential. Put C1 back unless its failed. You should be able to get a replacement cap if desired from any electronics place, such X2 caps are very common place. Mouser, Digikey, Farnell, Bitsbox, your local so-and-so.

If the 330uf caps were that bad they would have prolly expolded already. Fuse F1 should be a T4A type fuse.

Uhm, no. UK, so 240V, meaning smaller fuse. T2A sounds right off the top of my head, though 3 would be plausible, too.

 

[fractalsoup]

Check the DC resistance of the live and neutral prongs of the plug (UK, so the shorter ones) with the power switch in the ON position (disconnected from mains, of course). Post that value.

4.5 Ohms between Live and Neutral on the transformer and 0L on the live and neutral prongs of plug socket

Then measure the DC resistance of the secondaries (again, amp still disconnected from mains). Note that the secondaries must still be disconnected from the rest of the circuit. Post those values.

0 Ohms (Wasnt sure which connector to which prong though 2 x Reds, Yellow, White, Black, White) But 0 Ohms between each one and across Primary to Secondary

 

[PelliX]

4.5 Ohms between Live and Neutral on the transformer and 0L on the live and neutral prongs of plug socket

Uhm, OK. The transformer value could be correct, but there should be the identical resistance on the plug prongs (and receptacle on the amp, same thing), assuming the switch is on and the fuse is intact. If you measured this with a blown fuse or the switch OFF - then it makes perfect sense, no worries.

0 Ohms (Wasnt sure which connector to which though prong though 2 x Reds, Yellow, White, Black, White) But 0 Ohms between each one and across Primary to Secondary

I think/hope you're mixing something up here; primary and secondary windings should have infinite resistance between them! If there truly is continuity between them, the transformer is shot - and in an uncommon way, too.

To measure the secondaries it's generally the colour pairs, I'm afraid the schematic I grabbed quickly didn't include colours. Someone else here probably has the info, though.