Blown amplifier part.

[Delta Prime]

Hello. I put the multimeter on each end of the blown capacitor exposed wire part and it read nothing when the unit was turned off but when I turned it on it read around 20 k ohms.

That 20k Ohm resistance measurements is erroneous.When making resistance measurements power should never be applied to the circuit.Your DMM itself provides a constant current source across your meter probes when you select the resistance measurement function. Ideally the component should be taken out of circuit if not at least (as I mentioned before in post number 17) one lead or one leg should be desoldered lifted above the PCB and one of your probes(your choice positive or negative) should be attached there
The other multimeter probe to the other side of the component.

https://maker.pro/forums/threads/please-explain-this-resistance-reading.291354/

Could I have the exact name of what I need to buy and a suitable place to buy it from please.

I'm quoting myself from post number five.

It is inferred that you know how to solder hence desolder.
Provide me the lead spacing and dimensions and I'll supply you with three separate distributors to choose from on your new capacitor.

I now strongly think that this is why my unit is showing no sign of life. I now think that when someone wazzed the volume up to fast it created a surge which blew it

You came here asking for help. Let's take it one step at a time.
I would like to see if I can find you an service repair manual or at least a schematic.

1980 Ferguson 3939 amplifier

Any other information you can provide would be helpful all the information that's printed or has survived in the front of the unit and the back of your unit will give me that much closer to a proper schematic.

 

[ZJS]

Yes. The resistance is zero when no power is on.
When I get time I’ll take the dodgy capacitor out and wire it without the dodgy capacitor. That’ll make the circuit complete as there’s obviously no power getting past that as the lights on the front are wired after that and they don’t light up.
What do you think???

 

[ZJS]

I found these. The gold one looks similar but I’m not sure…?
Thanks

 

[ZJS]

Sorry I got it wrong. When power off it measures 20 k ohms

 

[ZJS]

Just taken that dodgy capacitor out.
Did the multimeter again and it showed up as nothing…
It’s dead for sure.

 

[ZJS]

Here.

 

[Delta Prime]

I found these. The gold one looks similar but I’m not sure…?
Thanks

They look a little small.
Do you think you can get a ruler and measure how far one lead is to the other lead & how thick & how long capacitor is. Please.
Your capacitor is a 3X.

Just taken that dodgy capacitor out.
Did the multimeter again and it showed up as nothing…
It’s dead for sure

Yes; it's dead for sure.

 

[bertus]

Hello,

I think you can use a X2 capacitor in place of the X3 capacitor.
The X2 has better specifications.
See this page for more info:

Safety Capacitors First: Class-X and Class-Y Capacitors - Technical Articles

Learn about Class-X and Class-Y capacitors, where they are used, and why they are referred to as

www.allaboutcircuits.com

Bertus

 

[Delta Prime]

Subclass is X2 used for home appliances and X1 used for industrial applications although both exceed X3 safety classification sacrifice is in size and price point it is why I keep asking for dimensions. This is the third time already jeez

 

[ZJS]

Hi, I found one on the internet and I ordered it. It’s the same as the original… a new one tho. I saw that these ‘rifa’ capacitor have a habit of exploding - someone even stating… ‘the exploding capacitor…!’
I have tried wiring it up without the capacitor and to no surprise… it didn’t work. So this capacitor must be needed. There’s also a switch type screw which says fuse underneath. I have turned it but nothing happened.
What fuse does this control….

 

[Delta Prime]

. I saw that these ‘rifa’ capacitor have a habit of exploding - someone even stating… ‘the exploding capacitor…!’
I have tried wiring it up without the capacitor and to no surprise… it didn’t work

Potential multiple failures. As previously mentioned by .Mr. @Harald Kapp . Post number four.

https://maker.pro/forums/threads/blown-amplifier-part.300611/post-1856477

 

[ZJS]

After examining the capacitor and where abouts it’s situated in the amp. It’s not a noise suppression capacitor more a capacitor which deals with power. It said it’s a kind of safety capacitor - hence why it blew when the volume was turned up too fast… and it made a pop sound so would tie in with the capacitor as it exploded.

I do hope this solves the problem…

 

[Delta Prime]

Appears the cap would be across the transformer line and neutral as one would expect so any measurement may be null and void unless the cap is disconnected at least one leg.

https://maker.pro/forums/threads/blown-amplifier-part.300611/post-1856491

 

[Delta Prime]

Your safety, 0.1 microfarad, x3 capacitor is there to filter, suppress or attenuate a voltage spike, anomaly, transient, the source of which is your local utility grid that you plugged into. The capacitor let out its magic smoke.

 

[ZJS]

I guessed that. Like a fuse…
when it comes in post ill report back if works
Thanks a lot

 

[73's de Edd]

. . . .more of a capacitor which deals with power. It said it’s a kind of safety capacitor.
Baah . . . .rubbish . . .balderdash . . .poppycock !

The SAFETY auspices of that class X type of capacitor, is being the safe manner in which it FAILS, in past olden times, the use of a COMMON paper capacitor across the AC line could . . .and did, in times . . . result in big bang-bang pyrotechnics and cause fires . . . . . . . . . .and resultant lawsuits.


Frankly . . . . I think that . . . . . placed across the AC line . . . . X type of safety capacitor . . . . failure that you find, is merely a surfactal "wart" and TOTALLY NOT being related to your unit not actually working . . . . . . PERIOD !

You might now get a REAL start, by getting the Ferguson System 25 cluster set . . . . being inclusive of the 3939 . . . . . . of schematics at . . . . . .

Ferguson 3934 Hi-Fi System 25 | Instant Downloads | UK Vintage Radio and Television Service Data

www.service-data.com

73's de Edd . . . . .

 

[ZJS]

Hi, I got the service booklet. Found this. The part it mentions towards the bottom which is mounted on the Mains transformer is the part which I’m focussing on.
It says towards the middle about the fuse mounted on the back.
There is a black screw type pod which sticks out of the back. It is highly likely that if there is a fuse, it will have blown.
How would I access the fuse which I assume is inside this pod??

 

[bertus]

Hello,

The fuse holder is likely something like in the link:

https://nl.farnell.com/en-NL/schurter/0031-3901/fuse-holder-5x20mm-panel-mount/dp/1651784

Just put a screwdriver in the slot, put a bit of pressure on the screwdriver and turn it about 1/4 turn.
Release the screwdriver and the insert will come out.

Bertus

 

[73's de Edd]

WHASSAMATTAHYOUSEENNYHOW ?



The units fuseholder / pod is in the two yellow mark-ups. with the white mark up being the holders end fuse cap .
In accordance with our esteemed Bertus's referencing . . . if correct . . . a standard slot blade screwdriver goes into the end slot and then is turned counterclockwise about a 1/4 turn and the spring loaded bayonet action pops the end cap out. . . . . . . .or . . . . .otherwise it is using threaded action and multiple turns finally lets the end cap pop out. Fuse in hand.

Now . . . . . the SECOND DUMBEST thing that you could do, is to find an open fuse and put another in and then turn on the unit . . . COMPOUNDING any initial problems.

Thaaaassssit . . . . .

Share the units schematic with us for further assistance.

73' de Edd . . . . .

 

[ZJS]

Hi I’ve opened it and the glass fuse inside has blown.