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Old 4th Jan 2017, 2:23 pm   #61
Hunts smoothing bomb
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Default Re: Tandberg Huldra 8 valve failure

Hi Lawrence,

I have just got both pictures in post #42 up side by side and you are quite right, C704 which shows the crack is actually connected between AC LT and -ve LT and C703 is indeed shown side on inbetween C702 and C701.

It still stands that C703 be tested in the way described though.

Sorry, crossed posts..


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Old 4th Jan 2017, 2:32 pm   #62
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Default Re: Tandberg Huldra 8 valve failure

I think that C704 looks like a prime fail for the future, so best replaced anyways.

Good fun this innit, multiple tabs open, magnify this, magnify that, scroll between umpteen posts etc, trying to remember what was last looked at and what it meant.

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Old 4th Jan 2017, 2:35 pm   #63
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Default Re: Tandberg Huldra 8 valve failure

Hopefully the edited picture in post #60 will make things easier.
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Old 4th Jan 2017, 11:31 pm   #64
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Default Re: Tandberg Huldra 8 valve failure

parts check i have placed the 3 components on the schematic using a photo of each piece to make sure i have the identified correctly all new reading with the ohm reading, to save on repetitive pic`s have included both reading on one photo. again many thanks for this, once established i need new parts, are there modern equivalents as long as they meet the specs?
Clive
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Old 5th Jan 2017, 12:08 am   #65
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Default Re: Tandberg Huldra 8 valve failure

From previous tests we already know that D702 is OK.

You cannot test C704 in circuit, as it's shunted by one of the diodes in D701. You'll need to disconnect it and retest, but it isn't the cause of the fuse blowing.

The results of testing C703 indicate that current from your meter is flowing through D702 in one direction and possibly down to chassis via a possibly faulty C702. Disconnect one end of C703 and retest it.

While the two caps are disconnected, test C702.
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Old 5th Jan 2017, 10:45 am   #66
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Default Re: Tandberg Huldra 8 valve failure

Any chance of a close up photo of the original fuse that blew? It might give an idea as to the severity of any current flow at that time etc.

Lawrence.
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Old 5th Jan 2017, 11:22 am   #67
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Default Re: Tandberg Huldra 8 valve failure

I note that the circuit diagram posted by the OP in post #64 differs from that in post #21. The circuit in post #21 gives the value of C704 as 0.01uF. The circuit in post #64 gives the value of C704 as 0.022uF. There is also an extra capacitor C705. It's very difficult to read the value of C704 from the pictures. Perhaps the OP could advise?

As the OP is in Canada I would suggest that "Just Radios" would be a good place to obtain 0.01uF (10nF) or 0.022 (22nF) caps to replace C704 and possibly C703, but unfortunately there's a minimum order charge.

http://www.justradios.com/
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Old 5th Jan 2017, 11:38 am   #68
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Default Re: Tandberg Huldra 8 valve failure

So far as I can make out post#21 schematic is an early version, post#64 schematic is a later version, top right of both full schematics give the serial number change.

Earlier serial number version:

http://sportsbil.com/tandberg/huldra-8-sm.pdf

Later serial number version:

http://sportsbil.com/tandberg/Huldra%208%20skjema.pdf

Lawrence.

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Old 5th Jan 2017, 1:28 pm   #69
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Default Re: Tandberg Huldra 8 valve failure

Forgive me if this has already been tried Clive but have you tried measuring the resistance across C702?

You may need to leave the meter connected for 20/30 seconds and watch the resistance rise as the meter voltage slowly charges the capacitor. This will generally mean that the capacitor is good.

Then again you may find that the reading stays very low and does not climb, this would indicate a short circuit somewhere on the HT +ve rail, it could be something as simple as a decoupling capacitor inside the set that has gone short to being a trapped HT cable between the chassis.

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Old 5th Jan 2017, 1:44 pm   #70
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Default Re: Tandberg Huldra 8 valve failure

Quote:
Originally Posted by ms660 View Post
Any chance of a close up photo of the original fuse that blew? It might give an idea as to the severity of any current flow at that time etc.
Hi Lawrence,

I'm reckoning that the fuse went with some severity as the OP stated that in post #1 that a flash was observed in the EM87 which was accompanied by a smell, the original thought by the OP was that it was the EM87 itself which expired, however the EM87 has since been tested for continuity and all seems well with it so in post #21 & #22 it has been presumed that what the OP observed was the flash from the fuse through the EM87 as it blew.

I'm certainly interested to find out the cause of this.

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Old 5th Jan 2017, 10:27 pm   #71
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Default Re: Tandberg Huldra 8 valve failure

Forgive me if this has already been tried Clive but have you tried measuring the resistance across C702? Hunts smoothing bomb

It's very difficult to read the value of C704 from the pictures. Perhaps the OP could advise? Station X

B]The results of testing C703 indicate that current from your meter is flowing through D702 in one direction and possibly down to chassis via a possibly faulty C702. Disconnect one end of C703 and retest it. Station X

Any chance of a close up photo of the original fuse that blew? It might give an idea as to the severity of any current flow at that time etc.
ms660

i put the quotes in to make sure i answered some of the questions see the latest photos, a couple more photos in the next post from me, i removed some wires so i could get out C703 out of the circuit otherwise very tight in there. i just recently looked at "just radios" looks they will be able to help when i am ready.............as they say when in crisis "put the kettle on"

Clive
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Old 5th Jan 2017, 10:30 pm   #72
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Default Re: Tandberg Huldra 8 valve failure

C703 tests OK, but it would be best to replace it along with C704.

It looks to me like you're testing D702 rather than C702.

You need to test C702 using the resistance range on your meter, not the doide testing facility.
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Old 5th Jan 2017, 11:22 pm   #73
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Default Re: Tandberg Huldra 8 valve failure

Graham, your right i keep getting my c and d`s mixed up
update on pic showing ID of components being tested, one still to come C702 resistance
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Old 6th Jan 2017, 3:48 am   #74
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Default Re: Tandberg Huldra 8 valve failure

here are the results for C702 measuring resistance.
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Old 6th Jan 2017, 10:09 am   #75
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Default Re: Tandberg Huldra 8 valve failure

This is interesting as there are no apparent short circuits on the HT rail, you have proved this by testing across C702.

It is hard to tell looking at the pic but is there a hair line crack in C703?

Replace these Rifa capacitprs anyway as even if they are good now, they are likely to cause trouble in the future.

The fuse does not look like it blew violently as there is no sputtering or blackening of the internal glass wall, I am puzzled where the smell came from though, it looks (at the moment) as though the fuse has failed under natural fatigue. Is it possible that the smell was not related to a fault maybe and is indeed a red herring?

Have you tried inserting a new fuse and disconnecting C703 and powering up?

Cheers
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Old 6th Jan 2017, 10:47 am   #76
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Default Re: Tandberg Huldra 8 valve failure

right now i am in a holding pattern waiting for some fuses from england i couldn't find anything here to try with. the 5x30mm size is very much a european size. the fuse when i took it out did have the end cap fall off so i glued it just to keep it for reference. i was looking at Just Radios parts found replacements for C703 and C704
(0.01uF 1000 VOLT "Tubular Axial" Met'd Poly Film)
http://www.justradios.com/cart.htm
but no picture would they be different in size and design to what i have. this will be the first time i have ordered these type of parts.
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Old 6th Jan 2017, 1:35 pm   #77
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Default Re: Tandberg Huldra 8 valve failure

C703 is 0.01uF 1000V DC

C704 is 0.022uF 400VDC This can be a much lower voltage. 100V will do. No harm in using a higher voltage cap though.

I recommend metallised polypropylene capacitors. You will need to choose C703 so that it fits in the gap (perhaps an orange drop type will do this), or you could fit a cylindrical cap on long leads.

It might be better to wait until you have the fuse and can try some more tests before ordering the caps, just in case you need more caps.

Is the fuse link resistor R241 still intact?
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Old 6th Jan 2017, 2:07 pm   #78
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Default Re: Tandberg Huldra 8 valve failure

One addition test you could do is to check that the mains transformer is OK.

No need to insert a 160mA fuse. Power up the unit and measure the AC voltage between chassis and each side of the holder for the 160mA fuse. You should measure 2 or 3 hundred volts on one side.
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Old 6th Jan 2017, 9:13 pm   #79
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Default Re: Tandberg Huldra 8 valve failure

Graham, here is the photos of R241, on the closeup of R241 you can see a burn mark on the resister where the vinyl shows discoloration and on the adjacent valve, don't know if that happened when i saw the flash.
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Old 6th Jan 2017, 9:16 pm   #80
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Default Re: Tandberg Huldra 8 valve failure

It's intact, but at some time it's come into contact with the adjacent cable sheath. Make sure that none of the wires within the sheath have been bared and could therefore touch each other.
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