Hifi amp has stopped.

[Portishead]

Hi.
I have a rega mira home hifi amplifier.
It stopped working today. I checked the internal 2a fuse and it had blown. I foolishly used a spare 5a fuse and the amp came on. I tiny bit of smoke came from a component so I quickly removed the plug.

Wondered if there is a technical wizard on here that could try and help me test, repair and get it going again.???

[budm]

Re: Hifi amp has stopped.

What is the exact model number, rega mira 3?
How about good clear pictures that shows all the boards and the one that smoked?

[Portishead]

Re: Hifi amp has stopped.

It is a Rega Mira cira 1998 I think. I have uploaded pictures to my album. Ill try and put them here.

Really really hoping you guys can help me out and tell me how to repair it.
I am pointing to the place that got smoky

[budm]

Re: Hifi amp has stopped.

Those are the Emitter resistors for those 3-pin output power transistors mounted on that black heatsink, you probably has shorted out transistors so you need to check the resistance of the of the Transistor between Collector and Emitter pins, you will probably find that some of them may show very low resistance.
What kind of tools do you have?

[Portishead]

Re: Hifi amp has stopped.

I would be forever grateful if you can help me bud. I only really have a multi meter like this.
http://www.amazon.co.uk/Draper-60792.../dp/B0001K9XKW

I have Plenty of small tools etc. Soldering iron...

But why did it blow the 2a internal fuse in the first place.?

They got very hot and are cracking thier cases. The little square black component has even started to melt.

What have I done

[budm]

Re: Hifi amp has stopped.

It blew the fuse because the components had failed.
So as I indicated, you need to check out the output transistors on that heatsink.
BTW, what is he exact model number? It has to have a sticker showing the full model number some where.

[Portishead]

Re: Hifi amp has stopped.

Ok, Just trying to find the model for you now. Not at home a sec.
It's like this model. I am sure there is only one. But I will double check and get you the model number if there is one on it.

http://www.ebay.co.uk/itm/Rega-Mira-...-/301920474059

So, can you just tell me what to set the multi meter at ? Can I test them in situ?
Shall I put the probes on the outside pins of each transistor?

[budm]

Re: Hifi amp has stopped.

Set the meter to 200-Ohm scale.
You have 3-leg device, so looking from the top you can assign left pin as pin 1, middle pin as pin 2, right pin as pin 3, then do the combination resistance testing:
1 & 2 = xxx Ohm.
1 & 3 = xxx Ohm.
2 & 3 = xxx Ohm.
I will try to see if there is diagram out there in the WEB.

[Portishead]

Re: Hifi amp has stopped.

Ok, I will test in an hour or so. Just to confirm, this is what I'm doing in the picture.

[stj]

Re: Hifi amp has stopped.

any chance of higher resolution pics?

[budm]

Re: Hifi amp has stopped.

Ok, I will test in an hour or so. Just to confirm, this is what I'm doing in the picture.

That will work.
BTW, that is an expensive amp.
http://www.audio-ideas.com/reviews/i...teds/mira.html

Did you try contacting REGA?
http://www.rega.co.uk/amplifiers.html

[Portishead]

Re: Hifi amp has stopped.

Will try to get higher res images

[Portishead]

Re: Hifi amp has stopped.

Yes, It cost a fair bit some years ago. Hence devastated but I'm quite happy to have a go at fixing it though with your help. I can get any parts if and when you decide whats needed. I havent contacted Rega, Theyd charge the earth I expect.

[Portishead]

Re: Hifi amp has stopped.

So, the meter is set to 200.(not 200k)

The top one reads :
1+2 - 00.3
1+3 - 00.8
2+3 -00.8

The bottom one reads :
1+2 - 00.4
1+3 - 00.5
2+3 - 00.5

[budm]

Re: Hifi amp has stopped.

OK, you need to remove them and retest them off the board next. The bad part is that I cannot find any diagram for your set yet, you also have bad driver transistors also.

[Portishead]

Re: Hifi amp has stopped.

Ok. I'll remove them now. There also another 2 lower on the board, should I test them or no.

What's the Bad driver transistors???

[budm]

Re: Hifi amp has stopped.

There are two output transistors per channel, so it should have 4 of those transistors on the heatsink.
Yes, you might as well check the other two also since one channel already failed.

[budm]

Re: Hifi amp has stopped.

'What's the Bad driver transistors???'
This is a great website for learning.

http://sound.westhost.com/project03.htm
For example: Fig. 1A, BD139, BD140 are the driver transistors for the output transistors MJE2955, MJE3055.
When you have direct couple circuits, when one device failed it will usually take out other devices in the chain with it.

[Portishead]

Re: Hifi amp has stopped.

Yes.the second set further down are as follows.
1+2 - 1
1+3 - 100.0
2+3 - 1

1+2 - 1
1+3 - 99.9
2+3 - 1

Making sense??

[budm]

Re: Hifi amp has stopped.

'1' on the meter means the resistance is too high to show on the 200 Ohm scale which is good news. They are fine.