Dansette Major - no sound

[shbs1960]

I've acquired a Dansette Major in a non-working state which I foolishly thought must be simple to fix! The turntable turns and the valve lights up but no sound comes out. After trawling this forum I decided that the triple electrolytic capacitor was the most likely culprit. I replaced this with three single caps but still no sound. Where do I look next?
Thanks in advance,
Stuart

[Steve_P]

It won't be that! Sorry. If that had gone kablewie then there would be a loud hum.

Is the valve lit? If not, try a new valve. Cheaper than the transformer.

I just had a look at a Major De-Luxe circuit, which I believe to be the same. Loss of HT - Try measuring the output of MR1 (DC) or the Input (AC). Hopefully it's the diode.

Cheers,

Steve P.

[julie_m]

Try feeding a signal from an MP3 player or similar, between the slider of the volume control and chassis. If you hear anything coming from the speaker, then the amplifier is working and you just need a new pickup cartridge (crystal cartridges are notorious for dying of old age; the Rochelle salt crystal eventually absorbs enough moisture from the air to dissolve itself into a puddle). The Ronette 105, available from Musonic, works fine in this record player (I've got one myself). This is a stereo cartridge, so you will have to order yourself half a metre of 4-strand pickup wire at the same time if the existing cartridge and wiring are mono; but it's also using an artificial ceramic material, which doesn't self-destruct over time.

If you get no sound from the amplifier, measure the HT voltage (on the speaker transformer primary; the pin that isn't connected to pin 7 of the EL84) which should be in the range 200 - 300V. If it's low, the most likely explanation is that the rectifier has died (early semiconductors do fail). You can replace this with a 1N4007 and 220 ohm, 1W resistor in series.

Otherwise, check the resistances of the primary and secondary of the speaker transformer and speaker (obviously you'll have to disconnect the transformer for these measurements).

If you need the circuit diagram, it's available up top.

[Darren-UK]

Hi Stuart,

They are indeed easy to fix because, like most Dansette offerings, there's nothing to them - so don't get too worried .

Firstly, failed or failing electrolytics will give a bad hum at the 'speaker if everything else below deck is in order. Try the following quick and easy checks......

1. Give the volume control a shot of switchcleaner as this might be faulty courtesy of dirt and/or tarnished contacts. Normally controls thus affected will give a loud crackle when operated though; unless they're really bad.

2. Power up, turn volume up, then touch with a bare finger the terminals of the wires leading to the cartridge. If a healthy buzz then emits from the speaker, the cartridge is duff.

3. Lift the deck and power up. Wriggle the valve in its socket to see if the problem is bad pin-socket connections. Beware of volts against bare skin though.

4. Examine wiring from cartridge to amplifer tag strip for any obvious problems. Look also for other knackered components and wiring, including the wiring to the loudspeaker.

If none of the above trace the problem, check the o/p transformer to see if it's providing output. Check the loudspeaker itself. Failing those, check the rectifier (a very common source of trouble) and try subbing the valve.

Let us know how you get on and we'll go from there if still no joy.

[shbs1960]

Thanks for the advice Steve.
The valve is glowing but I don't suppose that means it is actually working.
I take it the diode is the square component that is connected between the big transformer and the little transformer. I measured 253VAC on one side and 330VDC on the other which seemed a bit strange as I would have expected a lower DC voltage if it is simply a diode. Any other ideas will be gratefully received.

[Michael Maurice]

Your voltage readings are correct, the reason that the DC output from the rectifier is 330V is because the 253V is the mean or average voltage of the sine wave, whereas the smoothed DC output is going to be the near peak voltage.

If you've ever repaired TV sets you'll probably know that a 240V AC input produces around 330V DC across the smoothing capacitor.

[shbs1960]

Thanks for all the advice.
I have fiddled about and broken a few brittle wires, hopefully got them back in the right places but the valve no longer glows so I may have got a wire wrong but I don't think so. I have bought a couple of valves from eBay so will have to wait until they arrive before continuing. I will let you know how I get on in a few days.

[julie_m]

Originally Posted by shbs1960

I take it the diode is the square component that is connected between the big transformer and the little transformer.

Yes, that's the one.

Originally Posted by shbs1960

Any other ideas will be gratefully received.

You've got HT. That means the problem isn't the mains ("big") transformer, rectifier diode or one of the capacitors. There should be a resistor between two of the capacitors' positive terminals, what voltage do you see at the other side of that resistor? (Should be somewhere between 200 and 300V). And at the third capacitor? (Should be quite low, less than 20V).

For the next round of tests, you will need to disconnect the loudspeaker transformer ("little transformer") temporarily. Check the resistance of each of its windings, and also the resistance of the loudspeaker. The primary should be a few tens of ohms; the secondary and speaker a few ohms each.

If the transformer turns out to be faulty, it can be replaced with one from almost any record player or radio using an EL84, UL84 or UL41 output valve. Someone here is bound to have one that would be better off broken up for parts and getting a chance to live on that way, than sitting in a sorry state at the bottom of their "when I get the time" pile .....

[shbs1960]

Thanks for the help AJS. I have 332V at the resistor, the same as at the diode. Zero volts at the third capacitor. The resitance of the speaker is 5.6 ohms, the secondary winding 1.1 ohms, primary 360 ohms. I keep getting 'belts' off the capacitors, is it safe to discharge them by shorting them and if not, how long do they normally take to discharge? Keep up the good work folks.

[Steve_P]

Well with the valve not in place or not lit, there won't be any volts there. We need to try and find out why that valve isn't glowing.

The heater, 6.3v AC, goes between pins 4 and 5. 4 goes to earth, 5 goes to the transformer heater winding.

Might be worth checking the 120 Ohm resistor across that cap to make sure it's OK.

If all this is OK, try putting a signal in at the volume control.

Cheers,

Steve P.

[shbs1960]

Still having trouble with my old Dansette.
Blew one of the capacitors by accidentally shorting it!
Changed the three main capacitors.
Have tried a new valve with no effect.
Fed signal from MP3 player into wires coming from cartridge and I get a very quiet sound out of the speaker. The volume control works but very little volume. Also have significant background hum.
Any more ideas folks?
Thanks again,
Stuart

[Steve_P]

Faulty cartridge. Need a new one.

http://www.musonic.co.uk/

Cheers,

Steve P.

[shbs1960]

I hope you're right about the cartridge Steve, it would certainly be an easy fix but what about the background hum when the cartridge is disconnected? Also, with the MP3 player attached would the volume be very low?

[julie_m]

Background hum is entirely normal when high-impedance inputs are left unterminated. As long as it goes (mostly) away with a resistor (or short) across the terminals, it's nothing to worry about.

This amplifier doesn't really have a bucketload of gain. My Dansette has an input jack that I wired up when I was younger, and when I've fed it from an MP3 player I've had to turn the MP3 player's volume up above a comfortable headphone listening level. The signal should be clear even though its quiet. If the amplifier is amplifying, though, that points to the cartridge.

[ben]

As for carts, I would look around for something like a BSR X5M , SC12H etc. readily available and cheap (including styli). I'm sure ebay will turn up one for about a fiver.

[Dr-Watts]

Having done a lot of these I'd reommend checking the HT and then test EVERY Resistor for change in value.
You'll be surprised how far out of spec they can be
I did an Dansette for a friend of mine that had very simular description, he'd replaced the C's but not checked any R's. Replacing all the out of spec R's cured the fault.
Thing is, there's so few of em, you may as well just replace the lot
The other thing to try is disconnect the cartridge and touch the wire, you should get a loud hum, if the cartridge has gone resistive (due to damp or whatever) it will mute the signal from your finger ~ So unplug it and try again.

Best of luck

Dr. Dave

[shbs1960]

Thanks for all the great advice. I'm going on holiday for a week so will get back to the Dansette next week and let you know how I get on.

[shbs1960]

Right enough, the cartridge was faulty. Fitted a new one but the volume is very low. It's a Ronette DC284 OV supplied as a replacement for the BSR X1H which was fitted. I also still have significant background hum. Any more ideas?
Keep up the good work,
Stuart

[ben]

Have you done what dr Dave suggested up there? this should cure the remaing faults...

[shbs1960]

Will change the resistors next, what sort of power do they need to be? Will 1/4 watt be OK?