Why are these fuses blowing

[Darin P-B]

Cheers

The fuses on the amp blow when it is powered up alone. I have a multimeter but not to sure what I am checking in this case

[pinkmouse]

Ok, in that case, it suggests to me that the output transistors in the amp have blown. This is not impossible to fix, but won't be quick or simple.

The first thing to do is probably see if you can track down schematics, either from Cyrrus themselves, or maybe via a google search.

[Richard C]

I think it's very similar to the Cyrus 1:

http://www.tcaas.btinternet.co.uk/cyrus1pwr.gif[/url]

[destroyer X]

You have two power cords.... three pins.... positive, negative and ground.... inside amplifiers may have those grounds soldered to the mains chassis... and audio sometimes, suspended from earth with 10 ohms resistor.

Lets imagine one of those cables with the ground broken inside... the ground will be made by the audio cables ground.. sometimes suspended ground.... when this happens, sometimes amplifier oscilates for microseconds and high consumption creating, lets see, some high frequency, short period oscilations.... this way fuses blow, because overcharge... lights remais because this do not affect them because if one fuse remains, you will have energy to regulator to keep lamps on (maybe small consumption leds...i do not know).

Also leakage..... measure AC in cabinet, in metal enclosure... one multimeter tip at metal and other point between your fingers and press it...measure if you have AC....having you have a damage transformer that is passing AC to the ground.

Just imagine those crazy things...no problem, if i told an foolish, will be better, just because hi knowledge people will not allowed such a foolish idea remains for a long time and will run to correct.

This way, will help all of us.

All OK!.... no more troubles in the world.... me speak english strange (sometimes as indian does)....my picture smile is also strange..one thinks is sadic, other thinks is kind, other thinks is ironic... how can i control their minds?.... i cannot!. So, some confused conclusions can be expected. Its all rigth.

Thank you for a new chance.

Carlos

[Darin P-B]

I worked out where all the transistors are (quite a few!) Not too sure where the output transistors are. But tested resistance and only seemed to get readings on the larger ones screwed to the heatsink ( 8 large and 2 small). Of the 8 large 6 showed a reading of about 120 and 1 was 0.5 and the other 1.5. The 2 smaller ones did not seem to give a reading - meter stayed at 1. The other little ones scattered about seemed to give a very breif reading and then just 1.

So does this mean the 2 on the heatsink need repacing? If it does and I replace them will they just fail again due to another problem somewhere else or do they just fail by themselves?

Really appreciate your help

Cherers
Darin

[Centauri]

Even though only two of the output transistors may be blown, it usually means the others have had quite an overload so all 8 should be replaced as a set. Sometimes this sort of fault can be caused by shorted speaker cables, or could have been the result of some smaller component failure. It is also quite probable that other components could have failed due to the output transistors shorting.

Best advice would be to seek the services of someone with power amp knowlege and decent test equipment.

Cheers

[richie00boy]

Centauri gives good advice

I replied to your email Darin, but you did not respond back to me...

Testing with a resistance meter is not really appropriate and can give different results depending on what meter you use and which way round you get the probes. You need to do a diode test, you can find how to do this in a basic electronics text book such as Horowitz and Hill (check your local library).

It would be very useful to know if the amp just died, or did it go under loud playing, plugging anything in or out, or shorted cables? This may have an impact on what else has blown.

I can deduce from your description of there being 8 transistors on the heatsink that you have an early Cyrus 2. Don't waste your time contacting Cyrus, their support is useless if they bother to respond at all.

It's quite likely that the two you measured as lower than the others are blown, but to be sure you need to diode test all of them and also the driver transistors.

However, if two have blown I would play safe and replace all the output transistors and their drivers. I even replaced the pre-drivers in the one I did. If you wanted to skimp a little you could just replace the output transistors and the drivers of the channel with the low measured devices in. The drivers are MJE343 and MJE353 and can be replaced with MJE340 and MJE350 which you should be able to find anywhere. The output devices are marked with Cyrus own cryptic marking, TIP41C (note must be this exact marking not A or B type) should be a suitable replacement.

[Darin P-B]

Thanks all for replys

Now these replacements transistors that aren't cyrus ones does this affect anything - such as quality of sound or amplification?

The seemingly faulty ones have the marking 644N at the top and then CYRUSPT - 7 at the bottom. And the other one (right next to it) 649N at top and CYRUSPT - 7 at bottom.

What sort of cost am I up for do you think - if it's just the transistors?

I appreciate everyones help on this... I now think it's time to hand over to a profesional.

Cheers
Darin

[Darin P-B]

PS - richie00boy, sorry did get your e-mail but thought I had replied. Yeah makes sense about the fuses, as when I first opened the back they were missing. I thought someone previous had not bothered to fix it, and then left the fuses out.

[K-amps]

Originally posted by Darin P-B
I thought the forum was supposed to be helpful, not cryptic

You Brits can't rest at the fact that a non-native takes the effort to learn your Language... you have to pi$$ on it when it doesnt fit your definition of being non-cryptic. Lets try and be a little appreciative... Carlos is a cool dude!

Carlos man, you are ok, don't worry about any criticism, your enthusiasm and contributions are welcome and appreciated.