Newbie looking for help with a Decca Capri

[stuboy57]

Yes the red and green wires are connected to the cartridge... no sound or anything even if I put my finger across the stylus......even when I put a replacement working cartridge in to check, also had the wires off the back of the cartridge and touched the 2 wires but nothing, also no louder hum when hand near cartridge

[stuboy57]

looking at the picture in #18 where the thin cartridge wires go to the connection where the big brown wire is, can I test anything there to eliminate there is not a break in the wires to the cartridge

['LIVEWIRE?']

You can test for continuity between the tagstrip on the underside of the deck and the wires which connect to the cartridge. In addition a signal from a known good source, ideally an AF generator or signal injector can be fed in at the tagstrip. If still no sound, and there is continuity from that tagstrip to the amplifier's input, the fault is in the amplifier.

[stuboy57]

Originally Posted by 'LIVEWIRE?'

You can test for continuity between the tagstrip on the underside of the deck and the wires which connect to the cartridge. In addition a signal from a known good source, ideally an AF generator or signal injector can be fed in at the tagstrip. If still no sound, and there is continuity from that tagstrip to the amplifier's input, the fault is in the amplifier.

Today I got a multimeter and tested for continuity between the tagstrip and the end of the wires that connect to the cartridge and all was fine as I got the beep from the meter...also I checked the other wires from the tagstrip back to the circuit board, and speaker wires.....all was ok, so looks like it could be the amplifier.......is the amplifier the big silver can.....also can you get replacements....can anybody guide me as how to check this also how to check for the 18v and 24v on the circuit...even some simple tests I can carry out.....I'm not going to let this beat me just need someone to show me what to and how to test the components and circuit
thanks for all the comments and help so far

[ms660]

The circuit board in your first post is the amplifier, all the components on it are part of the amplifier as a whole, the board is called a printed circuit board, often referred to as the PCB, I would say that replacement parts or substitute replacement parts for the amplifier circuit are available.

First you need the service manual, it will contain the schematic (circuit diagram) and should also show the physical layout of the various components, their electrical values and working voltages etc. You really need that before you start is my advice.

EDIT: By the way the big silver can contains two capacitors, one is the +ve (positive) supply rail reservoir capacitor and the other is the +ve supply rail filter capacitor, they don't perform an amplifying function, it's the transistors that do that, all should become be clear after you've perused through the manual a couple of times coupled with a few more posts/replies in this thread.

Lawrence.

[stuboy57]

Originally Posted by ms660

First you need the service manual, it will contain the schematic (circuit diagram) and should also show the physical layout of the various components, their electrical values and working voltages etc. You really need that before you start is my advice.

yes I have downloaded the service manual. I'm not very good at understanding electrical diagrams just need someone to guide me... I love a challenge

[RojDW48]

It's tempting to see the printed circuit board (pcb), which is the bit on which the parts of your amplifier are mounted, as the same as the circuit diagram - but it isn't. The diagram is a schematic layout of the circuit - the pcb is a convenient way of putting that circuit together. This little guide is fairly helpful - http://www.instructables.com/id/HOW-...CUIT-DIAGRAMS/ and will hopefully give you an insight into how puzzling it can be.

[ms660]

One of the most expensive thing to replace (if you can ever get one) would be the motor, so might as well start there, there is a winding on the motor that supplies the power to the amplifier board, so I would check that out first, the voltage from that winding on the motor will be AC and it should, when the mains power is applied and the on/off switched on, be approx. 18 volts AC, so far as I can make out from your pictures the 18 volt AC feed from the motor to the amplifier board is via the red wire and the white wire from the motor, if that's the case then follow those two wires back to the amplifier board, where they are connected there is where you need to measure the voltage...between those two connections, your meter must be configured to measure AC voltage.

Usual safety rules apply, don't forget that the tags on the on/off switch are live with a potentially lethal mains voltage on them, keep your fingers well away from the meter probe tips when doing any measurements. Obviously the power will have to be applied to the player and the on/off switched switched to on in order to do any voltage measurements. Please take care.

EDIT: PS...Make sure you don't short anything out when applying the meter probes to the PCB or any components.

Lawrence.

[David G4EBT]

Ooops cross posted with Lawrence.

Unfortunately, the service data is sparse. It contains only the circuit and list of components, so an ability to trace the signal path through from the front end of the amplifier by reference to the circuit only is called for. The fact that you can hear a hum from the speaker when a disc is playing may be a good sign because it can be an indication that the amplifier is working, if only after a fashion.

I've annotated the picture of the printed circuit board that you attached to an earlier post.

Ordinarily, after voltage checks have been carried out and compared with the circuit diagram, it would be customary to use a signal injector to inject an audio signal at the wiper of the volume control. If the amplifier is working, a loud tone would be emitted from the speaker. If not, the injector would be placed at various point such as the base of each transistor to locate the fault. In the absence of a signal injector, if you scratch the tip of an insulated screwdriver on the centre pin of the volume control, (which looks to be where the green wire is attached in your case), if the amplifier is working, you should hear loud scratching noises from the speaker. If such noises are heard, then it can only be the front end wiring from the stylus and wiring to the input of the amplifier which is causing the silence.

Do bear in mind that any voltage tests you carry out can only be done with the motor running as it is the motor that also acts as a transformer to provide 18V AC to the rectifier, and from there, 24 V DC to power to the printed circuit board. If the motor switch is off, there will be no power to the rectifier or from there, to the amplifier. On no account must you go near the four tags on the rear of the volume control as those uninsulated tags are connected directly to the mains.

There is also mains voltage on two tags of the motor, and on the motor switch, so bearing in mind that there are exposed live connections direct from the mains, and that to do any live testing on the amplifier, (which is powered by 12 volts DC so is safe to work on), extreme caution is called for around those areas which are live. Some forum members, including myself, would only work on such equipment via a mains isolation transformer. In this instance, I wouldn't actually plug the equipment into the mains to do any voltage tests or diagnosis - I'd power the amplifier from an adjustable power supply to provide the 24V so I could work in complete safety.

To check if there is 24Volts DC to power the amplifier, you need to have your multi-meter set to DC Volts. The large metal can is the twin unit smoothing/reservoir capacitor. You need to check if it only has two tags and wires underneath it. If so, they will be the positive connections and the can itself will be the negative connection for both capacitors. If this is so, you need to connect the red test lead of your multi-meter to each tag in turn, with the black test prod on the can. If all is well, there should be 24 Volts or thereabouts shown on the meter. I would reiterate that to carry out this test, the motor must be running.

If there isn't 24 Volts DC, that's an indication that the rectifier is faulty. If there is 24 Volts but the 'scratch test on the volume control produces no sound from the speaker, then fault tracing is called for to track down defective components. Working or not, personally I'd routinely replace the four small electrolytic capacitors C1, C3, C4, and C7 in any event. It looks to me as though someone may possibly have removed a component from the printed circuit board as there are tell tale signs around two holes that suggests heating by a soldering iron. I may be mistaken - you'd need to check. I've highlighted them on the annotated picture of the board.

Please heed the warnings about safety. This information is given in good faith and without liability by anyone on the forum - you've been warned, and you ride at your own risk. I'd reiterate that in my view, despite your evident enthusiasm and desire to learn, (which is why I'm writing this post), you have no prior experience of working on electronics, don't understand what the role of each component is, and apart from the multi-meter, have no other diagnostic equipment. Simply de-soldering components on that type of printed circuit boards isn't an easy task without lifting and damaging the copper tracks.

I'd reiterate that in my view, you really need someone to mentor you directly on a one-to-one basis - not simply exchanging posts on the forum, but so far, there have been no takers.

I hope this information is helpful.

Good luck in your endeavours, and take good care.

[ms660]

The Trader sheet shows the component locations on the board.

Lawrence.

[David G4EBT]

Originally Posted by ms660

The Trader sheet shows the component locations on the board.

Thanks Lawrence - so it does.

I'm using Paul's DVD-ROM and under 'Decca Capri' only the 'Radio Servicing' Data is included.

However, I've noted that the Decca model number for the 'Capri' is 'RP199' and I've just located that on Paul's disc further down the index - Trader Sheet 1894, which - as you say - does have the layout of the PCB, which is a great help. Though the rectifier is referred to as 'MR1' inferring that it's a metal rectifier and thus might be suspect, in fact it's a typical silicon bridge, which hopefully will be working as it should.

The PCB appears to have 'Erie' PCB style resistors with metal end caps, which in my experience, tend to be reliable and to not drift high in value. Easiest place to check the 24V HT line would be by scratching the paint off the LH end of R11 (5.6 Ohms), located just below the rectifier, adjacent to the smoothing/reservoir can. It's worth having the 'Radio Servicing' data sheet too, as the circuit is a full A4 page, and the voltages are more clearly annotated.

I'd referred earlier to the PCB showing signs that at two holes (which I'd highlighted on the picture), it looked like a component - a cap or resistor perhaps - may have been unsoldered and removed. On looking at the diagram of the PCB layout, there appears not to have been a component of any kind at that location, so hopefully, the Capri hasn't come to the attention of a 'phantom fiddler' in it's life of more than four decades.

[Station X]

Five posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=134123

[stuboy57]

I have just read the posts in the other thread and totally agree with you, I have very limited experience with electronics apart from an electronics kit back in the late 60's, you know the ones with small springs that you put resisters, wiring etc on.

I think I will leave well alone as I don't want to electricuted!....best thing I can do is send it to someone to repair.

I find it hard to learn from books but on a one to one basis and someone showing me I would learn quickly.

Perhaps I would be better starting with a battery powered radio? What do you think as I have seen a couple?

[stuboy57]

thanks for all your comments and advice....all sounds rather daunting and working with live electric I don't want to be electricuted as I don't know what I am doing...it's not worth the risk!.......but if someone wants to look at it for me and repair it I could send it to them......I have just read these posts and totally agree with you, I have very limited experience with electronics apart from an electronics kit back in the late 60's, you know the ones with small springs that you put resisters, wiring etc on
I think i will leave well alone as I don't want to electricuted!....best thing I can do is send it to someone to repair.
I find it hard to learn from books but on a one to one basis and someone showing me I would learn quickly......
Perhaps I would be better starting with a battery powered radio...what do you think as i have seen a couple
or whats a good thing to start with

[RojDW48]

It seems to me that what is alarming some members here (me included) is the idea of someone attempting the repair of equipment about which they know nothing at all. Why not take a look at some internet tutorials on simple transistor amplifier design and see if you can identify the bits they describe on your amp - eg, find out what the smoothing/reservoir capacitors do and where they are, what is the level of signal going into the amp and compare it with the level coming out to the speaker - etc. When you have some idea of what the parts of the amp do and where they are, come back and try again. Here's a start, but there is plenty of info out there - try to find one that seems clear to you - http://www.explainthatstuff.com/amplifiers.html

[vidjoman]

In your Decca you have high voltages from the incoming mains to and from the switch to the motor. The amplifier is low voltage, as is most transistor equipment. So look first at the incoming mains wires and where they go to. Make sure you don't touch them and you should be safe. Of course if you unplug it from the mains it will be safe to work on, but not possible to run. You could cover these connections with a small polythene bag and secured by an elastic band to reduce any risk of inadvertently touching them.
It's different with valve equipment as they run on high voltages throughout and need extra care. Your current project only has a few hazards - just keep fingers away from the mains power parts and you'll get it working and learn as you go along.

[Hunts smoothing bomb]

I agree with vidjo man,

Don't hang up just yet on this, take in the information, watch a few basic electronics tutorials and get familiar with the discrete components and what they do.
Then go back to it, there is no rush, take your time. This really is a wonderful hobby.

Cheers

[AC/HL]

A more modern design would probably have had the mains connections better insulated, so would have been much safer to work on. To be fair to Decca (and manufacturers in general) they weren't designed for self maintenance.

[crackle]

Originally Posted by David G4EBT

The PCB appears to have 'Erie' PCB style resistors with metal end caps, which in my experience, tend to be reliable and to not drift high in value.

I am not so sure about those push fit resistors, I have found them to be rather erratic in value.

Mike

[stuboy57]

Originally Posted by vidjoman

In your Decca you have high voltages from the incoming mains to and from the switch to the motor. The amplifier is low voltage, as is most transistor equipment. So look first at the incoming mains wires and where they go to. Make sure you don't touch them and you should be safe. Of course if you unplug it from the mains it will be safe to work on, but not possible to run. You could cover these connections with a small polythene bag and secured by an elastic band to reduce any risk of inadvertently touching them.
It's different with valve equipment as they run on high voltages throughout and need extra care. Your current project only has a few hazards - just keep fingers away from the mains power parts and you'll get it working and learn as you go along.

Thanks for the positive comment....like your top tip for covering the mains wires....they connect to the on/off volume knob...I don't like to be beaten....lets do it one step at a time