Is my amp dead for good?

[David Jayne]

When the phone rings, a qualified tech rarely answers the soldering iron...

 

[TH63]

The fuse could be melted on the end where you can't see it. Not the middle. It should be checked with an ohm meter.

Just opened the amp and checked internal fuse, unfortunately it is also OK....

 

[TH63]

Let’s step back and debug the problem by breaking it down.

1) Test your wall outlet by plugging in another appliance. Test you amp in another room that is on a different circuit breaker.

2) The power cord on the BH250 is detachable. Remove it from the amp, then reinsert it, making sure that it is properly seated. Test the amp.

3) Test the power cord by plugging it into another appliance. If you can’t do that, a local repair shop should be able to check just the cord out for you.

4) Some 240 vac power cords have a fuse in the plug. If this is the case, you’ll need to check that fuse. Fused plugs can either be disassembled or there is a way to pop the fuse out. You’ll have to inspect it to see.

5) If the wall outlet and the power cord are fine, the next step is to have the amp checked out. If the internal fuse is glass, it is easier to see if the fuse has blown but not always. A ceramic fuse may not show any visible sign that it has blown. Ideally you want to test the fuse with an ohm meter. If in doubt, change the fuse with one of the correct ratings. Some amps have more than one internal fuse.

In general, I unplug all my amps when they are not in use. The slight inconvenience is well worth while.

Best reply so far. That's exactly what I'd do.

 

[Kevin1960]

If you are going to offer troubleshooting help to somebody who probably doesn't by his own admission understand electronics very well, I'm going to suggest that it would be helpful if you yourself understood more about the amp that you are offering (incorrect) information about.

On these types of amps, it's unlikely that you will see any continuity because the transformer is siolated from the plug by a bunch of other components, including a LF bridge rectifier and FET bridge switches. In the case of this amp in particular, there are also components that control the input voltage doubler.

The rest of your troubleshooting information has absolutely no relevance to this amp or most other amps either. You are mixing little bits from all kinds of different topologies, which tells me that you are a hobbiest that probably doesn't understand what you are saying, and this sort of advice could lead somebody else down the road to a dangerous situation. You have mixed bits from solid state and tube amps in the same troubleshooting suggestions, NONE of which apply to the OP's amp.



Correct, the comments above show how bad information gets perpetuated throughout the internet, and the scary thing is that plenty of people believe this crap, some even get hurt doing stupid things! (especially when the mains voltage is 230V)



The only exception is where the parts are held in place by epoxy dots, these can be very difficult to remove if they are sitting on top of fine traces without damaging things.

All of this should be taken as Electronic Bible study 101. I would also add that any Professional Tech. without a manual is feeling around in the dark and must rely upon their experience with that specific make and model if they hope to make any progress on a repair like this. Often times I wouldn't even waste time looking too deeply into something like this without a road map (Service Manual).

 

[subdude67]

Hello,

So far I have not been able to find a NTC D10-11 thermistor here in Kenya. Is there anybody here who can point me to a place where I can order one, preferably in Europe?

Thanks!

 

[Bassmec]

Hello,

So far I have not been able to find a NTC D10-11 thermistor here in Kenya. Is there anybody here who can point me to a place where I can order one, preferably in Europe?

Thanks!

Well I can't find an NTC D10-11 anywhere on planet earth, so are you quite sure it's not actually an NTC 10D-11.
10PCS NTC 10D-11 thermistor Thermistor High Stability | eBay
Looking back at your photo's it appears you are looking for the wrong or non existent part.

 

[beans-on-toast]

Yes, NTC 10D-11 as shown in the image. (Sorry.)

 

[subdude67]

I just got a break, a friend of mine is currently in Germany returning to Kenya in 10 days, he has found the thing and will bring it

 

[seamonkey]

Just one? The replacement could blow as soon as you plug it in if you don't check things downstream from it first.
Or you could luck out.

 

[subdude67]

Just one? The replacement could blow as soon as you plug it in if you don't check things downstream from it first.
Or you could luck out.

Good point, thanks!

 

[agedhorse]

When working on an amp where you have replaced an NTC thermistor, ALWAYS protect yourself against injury when powering it up. If there is a short and no current limiting, those devices can explode (loudly too) and take out an eye. There is a lot of concentrated energy being dissipated under this condition.

Really, safety is kind of a big deal for real.

 

[subdude67]

When working on an amp where you have replaced an NTC thermistor, ALWAYS protect yourself against injury when powering it up. If there is a short and no current limiting, those devices can explode (loudly too) and take out an eye. There is a lot of concentrated energy being dissipated under this condition.

Really, safety is kind of a big deal for real.

I will certainly heed your advise, thanks a lot! I will report back once the component has arrived.

 

[subdude67]

Finally i received the the replacement thermistor. Now I see this sticker on the package of the part:

What do I have to pay attention to when soldering the thermistor into place?

 

[Downunderwonder]

Dunno, but would you pm the ELF guy with some encouragement please? He put 240v up his 110v amp and blew it to bits, a very unlikely fix, but it would nice to find out the result.

 

[delta7fred]

What do I have to pay attention to when soldering the thermistor into place?

It requires no special handling techniques, you would have to try very very hard to damage it.

They probably pack everything in those bags so that nothing gets shipped in a normal plastic bag.

 

[beans-on-toast]

The sticker on the bag is common, no handling precautions are required.

When soldering, too much heat can be an issue. It can damage the circuit board traces or on delicate parts, the component itself.

 

[seamonkey]

It is a good idea to have a proper grounded (through a resistor) wrist strap and bench cover.
It may not be this particular part that you zap as you insert it.
Safety glasses too - as flux spits.

 

[subdude67]

Thanks guys, just want to make sure I'm not accidently stoppig he earth from spinning

 

[Kevin Colt]

Take an ohm meter and start checking continuity, put the leads across the two plug ends, this should read about 6-8 k. That will tell you if the primary of the power transformer has been affected. Also pull that fuse and check it too, I've seen them go bad without showing any sign of being burnt. If you can disconnect the power switch and check it too, an over voltage on it could have damaged it without any signs. I doubt if it went any further than that (I could be wrong), those seem like the most likely places to look.

 

[delta7fred]

Take an ohm meter and start checking continuity, put the leads across the two plug ends, this should read about 6-8 k. That will tell you if the primary of the power transformer has been affected. Also pull that fuse and check it too, I've seen them go bad without showing any sign of being burnt. If you can disconnect the power switch and check it too, an over voltage on it could have damaged it without any signs. I doubt if it went any further than that (I could be wrong), those seem like the most likely places to look.

The BH 250 is class D amp with a switched mode PSU so it won't have a conventional PT.