amp been in for repair, not fixed need advice to trace faults

[mrlennon]

Thanks mark stones,

i only wanted 2 resistors howver i just tryed to order there is a minimum order value of £20 at farnell
but thanks for the link anyway mark.
thought it was too good to be true

i ordered rest of parts from dalbani, some are on there way rest on 7-10 day order, however they did not stock the resistors.



ok had another quick look on maplins website would this be ok for the origanal Min Resistor 75 OHM 1/5W

Min Resistor 75RMetal Film 0.6W

• Working voltage max.: 250V
• Tolerance: 1%
• Power rating: 0.6W at 708C
• Temp. coefficient: 50ppm/8C
• Dimensions: 6.5mm x 2.5mm dia.

http://www.maplin.co.uk/Module.aspx?ModuleNo=-9393&doy=19m10

also will this be ok for the origanal Min Resistor 22K OHM 1/5W

Min Resistor 22kMetal Film 0.6W

• Working voltage max.: 250V
• Tolerance: 1%
• Power rating: 0.6W at 708C
• Temp. coefficient: 50ppm/8C
• Dimensions: 6.5mm x 2.5mm dia.

http://www.maplin.co.uk/Module.aspx?ModuleNo=-9431&doy=19m10

 

[anatech]

Yep, go for it.

-Chris

 

[mrlennon]

ok just a update still waiting for my parts to arrive, hopefully in next few days,

quick note, i have found a koshin 63v 470uf cap blown on the amp, anyone know if i will need to get the origanal koshin cap will it affect the sound if i use a sub cap? or would i get away with useing a normal 63v 470uf cap ?

or any one got a source for the koshin cap?

thanks

 

[EchoWars]

Don't obsess on brand names...other than to avoid the ones you never heard of (and I never heard of Koshin...blessed by a Rabbi maybe?)

Put a decent Panasonic FC or Nichicon in there and don't worry about it.

 

[Stones]

Thanks mark stones,

i only wanted 2 resistors however i just tried to order there is a minimum order value of £20 at farnell
but thanks for the link anyway mark.
thought it was too good to be true

i ordered rest of parts from dalbani, some are on there way rest on 7-10 day order, however they did not stock the resistors.

If there is an RS or farnell trade counter close to you can just go in and order as little as you like.

ok just a update still waiting for my parts to arrive, hopefully in next few days,

quick note, i have found a koshin 63v 470uf cap blown on the amp, anyone know if i will need to get the origanal koshin cap will it affect the sound if i use a sub cap? or would i get away with useing a normal 63v 470uf cap ?

or any one got a source for the koshin cap?

thanks

Was that cap close to something that got hot? Consequently melting the caps outer jacket (you can just cut the jacket off its not required unless something else can short with the cap's body). I digress, is the cap dead? Can you test it?

If it's dead then what he said RE: Put a Panasonic FC or Nichicon in there and don't worry about it.

 

[mrlennon]

the cap is defenetly gone, as its not charging,

ok some of the parts have arrived today,

2SD600K

Power trans

16v 100uf cap

An externally hosted image should be here but it was not working when we last tested it.

also can i use some heat resistant grease for the power trans as i lost the orignal paper backed ones as in picture below.

 

[anatech]

Hi mrlennon,
The original "paper" on the outputs are made from mica. You need new ones. The grease is thermally conductive heatsink grease.

Please order both, they are very important.

-Chris

 

[mrlennon]

will these pads be ok,

http://www.maplin.co.uk/Search.aspx?criteria=mica&doy=21m10&source=15

thanks

 

[mrlennon]

i might go and buy some of these as they are better than the micra ones also you dont need heatsink compound with them.

 

[anatech]

Hi mrlennon,
I don't trust easy. For good reason. I highly recommend you go with these and heatsink grease. Might be a touch more work but I know they work. I find pads work better with a thin film of grease (depending on the pad) and pads may "cut through" easily. You don't want to know about cut through!

-Chris

 

[mrlennon]

ok mate thanks will buy some of them instead,

would u say this grease is ok http://www.maplin.co.uk/Module.aspx?ModuleNo=30171&doy=22m10D

 

[anatech]

Yup, buy the small size. Most people apply too much. Use an even, thin coat. Only a little bit should come out from the sides when you tighten the part down. Don't over tighten the parts.

Cheers & good luck!

-Chris

 

[mrlennon]

ok thanks anatech for the advice,

what i found strange is the old power transistors i took off the heatsink had no traces of grease on them? just attached to the micra pads?

i am assuming i use the grease on the back of the power transistor then the micra pad obviusly goes to the headsink.

or should i place some grease front and back of pads for better heat transfer?

 

[anatech]

Yes, that is the accepted pratice. Revox for example used to mount the parts "dry". The military does, or did to avoid mildew in the tropics.
Use heatsink grease.

-Chris

 

[mrlennon]

ok update still waiting for the rest of parts not arrived yet as of today hope they arrive soon,

can i ask a quick question i have a ceramic cap which i think is completly dead as its not charging and im not getting any reading from it,

it states its a 0.022UF 50V ZF does this mean its a 0.22UF 50V or just a 22uf 50v as the 0 at the beggining is misleading ?

also i need to replace a carbon resistor 560 OHM 1/5W
will this one be ok as a replcement?

resistor link

thanks

 

[anatech]

Hi mrlennon,
That resistor will do fine as long as the wattage is the same or larger.

Your 0.022uF cap will not cause a deflection on your meter, it will measure open. So it is probably good.

-Chris

 

[mrlennon]

ok after going through what parts i have what stranges also is in the service manual it states one of my min resistors burnt are 75 OHM

(brown,green,black,gold)

yet i work it out to 15 ohms? am i right as the service manual might be a typo error?

 

[johnnyx]

If you have a diagram, then go off that. Sometimes if a resistor has overheated, the colours change. The pigments aren't stable once it starts to burn, then you get black, black, black. Worse is where a yellow changes to brown, so you fit 100Ohms where it should be 100kOhms There are different coding schemes too, four band, five band, additional tempco band...It gets tricky .

The brown in the photo does look purplish to me though, but then the black looks more like brown so maybe it's just the photo.
You can get a good idea of the right decade by seeing where it is in the circuit, and it helps if the one in another channel is intact.

 

[anatech]

Of course, that resistor may have been changed before. Now it has the wrong value.

-Chris

 

[mrlennon]

yep it was changed i have now replaced it with the origanal ohm.

can i ask what value do u think this 5 band carbon resistor is in picture?

its a quite large carbon resistor.

no value in the service manual?.

i seem to have mislaid the origanal, but i hink it was fried thats why i took it out.

am i right in thinking its a 18 ohm, with 10 minus or plus tolerence?
thanks