MDA fuse for a glass fuse.

srinath · 2013-04-21 10:02 pm

I have an mda fuse in one amp that blowed up.
Can I put a 250v glass fuse in its place ? is the mda slow blow or something ? Thanks.
Cool.
Srinath.

JonSnell Electronic · 2013-04-21 11:23 pm

Read what it is printed on the label and look at the specification. Then decide for yourself.

srinath · 2013-04-22 12:13 am

I cant find the B&K manual, but I suspect this guy is a slow blow ... that I tossed in a fast blow and promptly blew one after the other - killing 4-5 ...

Anyway I better find this guys schematic or I am toast.
Cool.
Srinath.

JonSnell Electronic · 2013-04-22 9:30 am

Maybe if you shared what the item is, part number/description and what it is used in, we could offer advice or an equivalent?

srinath · 2013-04-22 1:15 pm

This is fuses F1 and F2 in a B&K avr 507 - and if you find the schematic or any thing on it please send me the link too. Its got MDA 2 written on it, I dont have any other details on it, and I think it has to slow blow, cos that cap isn't filling up. Thanks so much.

Cool.
Srinath.

AndrewT · 2013-04-22 4:20 pm

power it up through a bulb tester.
That will show if there is a fault.
Then you can try a T rated fuse.

Spiny · 2013-04-22 9:00 pm

If this is the fuse then its a time delay (slow blow) fuse
bussmann MDA fuse pdf

alan

srinath · 2013-04-23 2:55 am

Thanks guys, I am buying a bunch of em ... this amp eats em ... need many cos i also cant find the schematics, so truly blind here.
Cool.
Srinath.

JonSnell Electronic · 2013-04-23 9:15 am

Sorry, I can't get the link to work. I will upload the service manual to my web site, post a link.

$c:\users\jon\downloads\B_and_K_AVR-507_service_manual$

JonSnell Electronic · 2013-04-23 9:27 am

Hope this helps.
Reference Documents

AndrewT · 2013-04-23 10:52 am

Looking at the data for these slow blow fuses shows the big safety advantage of adopting close rated fusing.

Take a 240VA transformer running on 240Vac supply.
Close rated fuse is F1A, (240Va/240Vac=1).
Normal rated fuse is T3.2A, (3*240VA/240Vac=3).

Look at the data for time to rupture @ 30A fault current for these two fuse values.
~15ms for the T1A and ~300ms for the T3.2A.

I know which I would rather have in the mains supply to the transformer.
Yes it means I have to fit a soft start, but that is a small price to pay for a factor of 20 faster fuse blow.

srinath · 2013-04-23 12:21 pm

Oh wow, thank you thank you thank you.
Cool.
Srinath.

srinath · 2013-04-23 1:12 pm

F1 and F2

OK its blowing the fuses F1 and F2.
And I dont have any charge in one set of caps. I will find the right number of them.
The fuse on the right blows when neither of the amp boards are connected. That cap also has no charge at all.
The one on the left (I will get numbers for it F1 or F2 too) is blowing only when the left amp board is connected.
I will get part numbers for each of these in a bit.
Cool.
Srinath.

AndrewT · 2013-04-23 1:14 pm

Have you powered up via a bulb tester yet?
Does the bulb light, or flash, or glow dim, or what?

JonSnell Electronic · 2013-04-23 1:15 pm

Check BR3 and BR4

srinath · 2013-04-23 1:35 pm

Oooo Harleyjon that was exactly what blew in my HK 800+ quad and my JVC 601.
I will get it opened up in a bit.

Thanks.
Srinath.

srinath · 2013-04-23 1:37 pm

No DBT

AndrewT said:
Have you powered up via a bulb tester yet?
Does the bulb light, or flash, or glow dim, or what?

I dont have dbt but this amp was powered up all along, I wasn't worried about any more blow up's ... I yanked it from the wall to get it home.

Cool.
Srinath.

srinath · 2013-04-23 6:12 pm

Fills the caps

AndrewT said:
Looking at the data for these slow blow fuses shows the big safety advantage of adopting close rated fusing.

Take a 240VA transformer running on 240Vac supply.
Close rated fuse is F1A, (240Va/240Vac=1).
Normal rated fuse is T3.2A, (3*240VA/240Vac=3).

Look at the data for time to rupture @ 30A fault current for these two fuse values.
~15ms for the T1A and ~300ms for the T3.2A.

I know which I would rather have in the mains supply to the transformer.
Yes it means I have to fit a soft start, but that is a small price to pay for a factor of 20 faster fuse blow.

This fuse fills the caps ... I think I have to have that slow blow in there. Else it blow all the time.
Cool.
Srinath.

Spiny · 2013-04-23 9:07 pm

Check the bridge rectifiers, just use an DVM on diode setting. I would expect them to have shorted diodes. Amps should not blow fuses all the time!

srinath · 2013-04-23 9:56 pm

This amp has no BR4, the location on the board has never been soldered to.
The caps c17 and c18 are not charging up.
I am in the process of pulling it apart.

Thanks.
Srinath.

MDA fuse for a glass fuse.

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