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Old 11th Oct 2011, 11:12 am   #1
sadcakes
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Default Dansette Conquest Auto Help needed!

Hello,
I am the owner of a previously working Dansette Conquest Auto, with the 6AT6/6AQ5 dual valve setup.

Having not used the player for some time (10 years or so without a service) when I turned it on recently there was a slight (fraction of a second) delay and then the house fuse box tripped.

I removed the valves and tried it once more and the same thing happened.
I then stopped!

I'd like to try and bring this back to life myself.

(Having recently built a guitar valve amp I think I would have the ability to do so and part of the reason is for the enjoyment of fixing things and the learning experience.)

However I do need some help!

Firstly, are these symptoms indicative of a short circuit within a particular component or of a failing somewhere else?

I am assuming that the best place to start will be replacing all the capacitors, however I cannot find a schematic online that matches my particular model (The PCB is labelled 4.1) The ones at ***********************
http://www.***********************/service/dansette.pdf are close but not exact.

What confuses me though is that by visual inspection I can only see a total of 5 capacitors on the board. Three in the can, a yellow 25uf Electrolytic and a disk ceramic between the can and one of the valve sockets.

Is this possible? or as I suspect, is it more likely that some of the lighter brown resistor type components are actually caps (in disguise!)?

I've attached a photo to show what I mean.

If this is the case, what is the recommended way to determine the values of these? Most appear to only have three bands, although some like the one between the can and the treble pot have 5 'dashes' (white, red, black, red, silver)

Otherwise, is there any other recomendations you can give? Like I said the player did used to work very well, out of the 6 or so I had back in college, this was the best one that I kept for myself.

Thank you in advance for any assistance

Sean
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Old 11th Oct 2011, 11:36 am   #2
Tim
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Default Re: Dansette Conquest Auto Help needed!

The fat bone shaped ones with three bands are indeed resistors, and follow the usual colour code(no tolerance band is an assumed tolerance of 20%. The ceramic ones with dashes are capacitors, these are generally very reliable types and will probably be fine unless physically broken.

When you say the house trip, I presume you mean the ELCB( main trip) rather than just the breaker for the ring main. If the former this in indicative of a live(or possibly neutral) to earth fault-short or leakage in excess of you trip rating(30 mA)-which is odd as you have a two core mains flex.. There might be a suppression capacitor from mains live to chassis, possibly on the deck. this might have gone leaky. The player will work without it, but if you want to replace it use a "y" rated type.
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Old 11th Oct 2011, 12:14 pm   #3
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Default Re: Dansette Conquest Auto Help needed!

Hi Tim,
Thanks for the swift reply!

I think it's just the breaker for main ring that is tripping - the sockets go off, but the lights remain on?

I hadn't thought to check the deck! I will do so this evening.

Just to confirm, when you say the 'ceramic ones with dashes' are you also refering to the bone type components that are the same as the aformentioned resistors (ringed in photo) or simply to the disk shaped ones (of which there is only one)?

Thanks again
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Old 11th Oct 2011, 12:51 pm   #4
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Default Re: Dansette Conquest Auto Help needed!

If it's blowing the 32A ring main trip, something is very wrong. The plug fuse should have protected that.

How recently was your house rewired? There was a trend recently to wire lighting circuits upstream of the RCD; the thinking being that plunging the entire house into darkness in the event of a fault was potentially more dangerous than the risk of a shock from a lampholder when replacing a light bulb. (Modern practice is separate RCDs for lighting and power circuits, so there is still earth leakage protection.)

If it is an RCD tripping, then this probably indicates faulty insulation somewhere inside the machine (fingers crossed it's not the power transformer). But first, make sure the plug is wired correctly -- connecting a double-insulated appliance between live and earth will work on an installation with no RCD.
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Old 11th Oct 2011, 1:10 pm   #5
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Default Re: Dansette Conquest Auto Help needed!

Hi Sean,

If it's tripping the RCD in the house it's probably a short circuit on the player. Someone may have fitted a high rated fuse in the plug on the player and if so the trip would more than likely work before the fuse. Visually inspect the components on the amp for burn marks or overheating and have a smell around the mains transformer for burning smells.

You need to be checking the mains transformer primary and secondary for short circuit readings and check the metal rectifier and smoothing capacitors before progressing any further. Also check the on/off switch - they do go faulty.

Good luck,
Tony.
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Old 11th Oct 2011, 1:11 pm   #6
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Default Re: Dansette Conquest Auto Help needed!

The maximum fuse rating that can be fitted in a "13A" plug is 13 Amp. So if the 32A Circuit Breaker is tripping the fuse in the plug must have been replaced by a nail.

Is it a Circuit Breaker or Residual Current Device (RCD) which is tripping? A consumer unit will normally have one or perhaps two RCDs, but many Circuit Breakers.
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Old 11th Oct 2011, 1:47 pm   #7
sadcakes
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Default Re: Dansette Conquest Auto Help needed!

Hi,
Thanks for all the advice!

I'm slightly embarrased now that I may simply have the plug wired wrong - would that do it? It's an old 2 core flex, both cream, one with a black stripe (yes I plan to replace this!) so it could easily be back to front..

My flat was converted about 20 years ago and was partially rewired only last year (new fusebox and placement) when I had some work done.

I think it's the RCD which is tripping as there are two of those on the unit seperate from the circuit breakers, but I'll have to confirm that later when I'm at home. It's certainly not unusual for it to trip and turn off all the sockets when a fuse goes.

Visual inspection of the board and components, transformers etc doesn't show any obviously worrying signs, no burn marks.

I'll take a good look this evening and report back.

Thank you again for taking the time to help.

Sean
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Old 11th Oct 2011, 1:47 pm   #8
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Default Re: Dansette Conquest Auto Help needed!

No the ones with dashes are caps. See attached pic.

If it IS your ring breaker then there's a real nasty short somewhere. If you're determined to go ahead why not build a lamp limiter:


http://www.vintage-radio.com/projects/lamp-limiter.html

Have you checked the mains plug yet? If all OK, test "into" the player's mains cord(unplug and check on plug pins) with an ohm meter and see what you can see. There should be a resistance of a few hundred ohms at the very least(with the deck switched off and player on switch on)
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Old 11th Oct 2011, 1:49 pm   #9
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Default Re: Dansette Conquest Auto Help needed!

Thanks Tim, actually that very project is on my weekend to do list already!
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Old 11th Oct 2011, 7:07 pm   #10
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Default Re: Dansette Conquest Auto Help needed!

If it's tripping the RCD and if it's wired with two wire flex, then the plug must be wired incorrectly. However this doesn't fit in with the player working 10 years ago unless the RCD has been fitted since then.

The wires of the flex should go to the Live and Neutral pins of the plug. The live pin will have a fuse in series with it and this should be 3 Amps, Not 13.
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Old 11th Oct 2011, 7:24 pm   #11
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Default Re: Dansette Conquest Auto Help needed!

Hi,
If the Valves in this player are 'E' series (EL84 for example) the player is most likely fitted with a mains transformer and this may have developed shorted turns, which would cause the problem that you are experiencing.

If, on the other hand 'U' series valves are fitted (UL84 for instance) it's a fair bet that the player uses AC/DC mains techniques and the possibility then is that one of the deck isolating capacitors (if fitted) between the cartridge and the volume control may have failed.

In either case another possibility is that the motor winding has developed shorted turns, this can easily be proved by disconnecting the motor wiring (looks like the Green and Brown leads coming from the mains switch in your picture).

Before anyone mentions that the RCD should only trip if the deck is set to the play position, in the case of a shorted motor winding, if the unit is an AC/DC one the motor would usually operate as soon as the mains is applied (via the mains on/off switch) in order to maintain the valve heater supply via its autotransformer winding.


Regards
Andrew
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Old 11th Oct 2011, 7:45 pm   #12
sadcakes
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Default Re: Dansette Conquest Auto Help needed!

Graham, Tim, Tony, AJS, Andrew and everybody else reading this.

All I can do is apologise for being a complete novice and waisting your time.

I honestly have NO IDEA how this has happened but.. someone (and this could not have been me!) had wired the neutral wire to earth!

I can only assume this was back when it was in a shared living room at college.. I'm now thinking that actually the last time I would have used this was back then, which is long over 10 years ago and closer to 20!

Oh dear… regardless I hang my head in shame. I can't believe I came onto the premium UK repair and restoration website asking all you experts for help with what turned out to be the most basic of issues.

Needless to say I shall be getting my coat and it may be some tie before I darken these doors again and when I do it will almost certainly be with a new alias!
;-)

Anyway, I have to say a big THANK YOU!

You guys suggested looking at the one thing I thought too obvious to check in my eagerness to rip the thing apart and find the elusive faulty capacitor!

You can only begin to imagine how relieved I am not to have taken this to a qualified tech only to be shown the plug wiring!

So to sign off - maybe for some time - I will leave you with a couple of shots of the fully operational Conquest Auto and my thanks.

Not a bad specimen really.

all the best
Sean
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Old 11th Oct 2011, 9:23 pm   #13
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Default Re: Dansette Conquest Auto Help needed!

Don't worry about missing the obvious; nine out of ten of us have done it at some time and the tenth isn't to be trusted! Glad it was easy to fix, anyway.

It's still worth replacing the capacitor from the anode of the triode to the grid of the pentode, even if you do nothing else. It's probably 10nF or 22nF, rated 400V. If this part is faulty, it can cause extensive damage.
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Old 11th Oct 2011, 9:28 pm   #14
sadcakes
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Default Re: Dansette Conquest Auto Help needed!

Thank you.
Yes, I will do that, I had read that that's the one to change if nothing else.
And it should be well within my abilities!

Again, I really appreciate the help here. Top Notch.
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Old 11th Oct 2011, 11:53 pm   #15
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Default Re: Dansette Conquest Auto Help needed!

The output valve in this case is the 6AQ5. The 6AT6 is a triode used as a small signal pre amp(presumably the diodes are deliberately shorted, probably to cathode).
As the previous poster has stated, the capacitor that needs investigating will take the signal from the anode of the 6AT6 to the control grid(g1) of the 6AQ5. This may well be the ceramic one indicated earlier, in which case it will almost certainly be OK. If you have a multimeter, see if there is any DC voltage between chassis and g1 of the 6AQ5. If there is any +ve voltage suspect the capacitor. Having said that every 6AQ5 I have come across has had grid leak.Pull out the valve and measure again to find out whether it's the cap or the valve.

Valve info here.

http://www.r-type.org/exhib/aaa0082.htm

http://www.r-type.org/exhib/aaq0033.htm


Looking at the base of the valves, with the gap at the bottom, pin one is the first one counting clockwise. So pins 1 and 7 are each side of the widest gap.

Good luck, and now you have found a fault I hope it will boost your confidence..

Quote:
ll I can do is apologise for being a complete novice and waisting your time.
Don't worry about it, we all have to start somewhere, and I learn something new every day from this forum. It's not a waste of time if it stops you getting a belt, and saves a piece of old kit from the skip in the sky and keeps it going for the future. Even better it might kindle an interest and spawn another enthusiast!
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Last edited by Tim; 12th Oct 2011 at 12:00 am.
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Old 12th Oct 2011, 8:49 am   #16
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Default Re: Dansette Conquest Auto Help needed!

I think credit goes to Tim for spotting the original fault back in post #2. The trouble with remote fault finding is that it's all too easy to make invalid assumptions like the mains plug being wired correctly. Despite this the player would still have worked on an installation without an RCD and this is what must have happened.

I have come across plugs wired neutral lead to earth and straps wired neutral to earth where two core flex is used.
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Old 12th Oct 2011, 10:32 am   #17
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Default Re: Dansette Conquest Auto Help needed!

Graham makes a valid and important point, earth/neutral reversal in mains plugs does happen I have been caught out with that in the past so I guess it's fair to say don't assume anything. I seem to remember bringing that topic up on wiring up isolation transformer outlet socket somewhere on the forum, that's a different topic though.

Lawrence.
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