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Old 27th Oct 2018, 1:45 pm   #1
Stuartb
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Hi guys,

I am trying to build a signal tracer injector kit from Velleman called the k7000 the first kit I bought years ago but when I power it up I get a constant loud tone in the speaker, so I recently purchased another and put it togethor however this one I cant get a tone to come out of the speaker when I connect the output to the input, what is happening no support from Velleman please could somebody help me

Here are a couple of photos of my k7000.

Thanks in advance, Stuartb.
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Old 27th Oct 2018, 4:20 pm   #2
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Default Re: Velleman K7000 Not Working

Hi Stuart, welcome to the forum. Can't help you I'm afraid, but it would be a good idea to attach the schematic and some good pictures of your circuit boards, both top and bottom views. That'll give us more to go on.

Andy.
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Old 27th Oct 2018, 4:58 pm   #3
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Default Re: Velleman K7000 Not Working

https://www.velleman.eu/downloads/0/...nual_k7000.pdf
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Old 27th Oct 2018, 5:25 pm   #4
Stuartb
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Default Re: Velleman K7000 Not Working

Hi guys,

Thank you for your warm welcome also for attaching the pdf which is exactly the info that I have, a search of google for Velleman K7000 brought me to this forum where one of your members has made several of these kits, I was rather hoping that he might spot the post and reply as he seems to know them inside and out, hopefully I can pick up some more info also as valve amps are something I used to mess with many years ago...

thanks
Stuart
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Old 27th Oct 2018, 5:36 pm   #5
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Default Re: Velleman K7000 Not Working

Hello Stuart,


I think you may have taken your resistors straight from the bandolier in the order they came. That will work but it looks from the photo as if you started at the wrong end. You have R1 fitted in the R11 position, R2 in the R10 position and so on. R6 may be in the correct position already if my assumption is right.

The correct colour code resistor for each position is listed below:

R1 220 ohms Red Red Brown Gold
R2 3k3 ohms Orange Orange Red Gold
R3 3k3 ohms Orange Orange Red Gold
R4 22k ohms Red Red Orange Gold
R5 100k ohms Brown Black Yellow Gold
R6 5k6 ohms Green Blue Red Gold
R7 1k5 ohms Brown Green Red Gold
R8 470k ohms Yellow Violet Yellow Gold
R9 2k2 ohms Red Red Red Gold
R10 100 ohms Brown Black Brown Gold
R11 10 ohms Brown Black Black Gold

ZD1 will have taken a bit of a battering if the 10 ohm resistor was fitted in the R1 position, other than that I don’t think any damage will have been done.

The on line manual linked above has a fairly clear picture of the resistor positions too.

Paula
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Old 27th Oct 2018, 6:01 pm   #6
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Default Re: Velleman K7000 Not Working

If frsimen is right then you broke one of the GOLDEN RULES whenever you start to build a kit....read the instructions....check that you have all the components against the listings....most of these kits have the resistors and the corresponding colour code marked out.

Anyway hopefully that is the route of your troubles and you can now sort it out. From what I understand, these work quite well although rather basic but they do what it says on the tin.

There is nothing wrong with that circuit and it should be pretty bomb proof
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Old 27th Oct 2018, 6:13 pm   #7
Stuartb
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Default Re: Velleman K7000 Not Working

Hi Frsimen,

Do you know this is happened because I did follow the instructions:

Axial Components Are Taped In The Correct Mounting Sequence !


The Zener diode being the first component and this is the end I started from so something is not quite right there then

Thank you for spotting it, I will take the board out and start again doing it my way.

Cheers
Stuart
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Old 27th Oct 2018, 6:58 pm   #8
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Default Re: Velleman K7000 Not Working

Hi,

I have removed all of the resisters and the zener diode, I think I have all of the resisters however I have a number of packets of small glass zener diodes but the packets are not marked is there an easy way to test a zener ?

Thanks
Stuart
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Old 27th Oct 2018, 8:52 pm   #9
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Default Re: Velleman K7000 Not Working

Hi all,

I tested the zener and OK so I put it back in, changed the resistors and bingo now working, big thanks to you all.

Cheers, Stuart.
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Old 27th Oct 2018, 9:21 pm   #10
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Default Re: Velleman K7000 Not Working

Well there you go then! Maybe Velleman need to be told that something is wrong. Their quality control needs improving!

With regard to testing zener diodes.....well if they are not marked then you need something like a 30V DC supply, a 10K* resistor and a voltmeter. Connect the 10K* in series with the cathode (usually marked with a black or red band) of the zener diode, connect the free end of the resistor to positive of the supply and the anode of the zener to negative.....zener diodes are reverse biased just in case you wonder why it seems to be connected backwards.... and connect the voltmeter across the diode. The meter should read the zener voltage of the diode.

*for low wattage diodes (up to about 400mW), 10K should be ok, for higher wattage you may need to reduce it but don't go lower than about 4.7K with a 30V supply. Obviously the above method is OK for diodes up to about 25V. If you have others that may be a higher voltage then you need to increase the power supply accordingly.
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Old 28th Oct 2018, 8:30 am   #11
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Default Re: Velleman K7000 Not Working

Glad you got it working, I forgot to mention checking the resistors, an easy error to make, we've all done it. 10 and 100r are particularly easy to mix up.

Andy.
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Old 28th Oct 2018, 1:05 pm   #12
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Default Re: Velleman K7000 Not Working

Quote:
Originally Posted by Sideband View Post
Well there you go then! Maybe Velleman need to be told that something is wrong. Their quality control needs improving!
It's difficult to see what more Velleman can do than they have, to help constructors to avoid pitfalls.

The high quality PCB is clearly screen printed with each component I.D, and the assembly instructions state:

*Make sure the skill level matches your experience, to avoid disappointments.
*Follow the instructions carefully. Read and understand the entire step before you perform each operation.
*Perform the assembly in the correct order as stated in this manual
*Position all parts on the PCB (Printed Circuit Board) as shown on the drawings.
*Use the check-boxes to mark your progress.

The pic below shows a completed screen-printed K7000 PCB.

The components are bandoliered to assist in the best order of construction.

But I'm certainly not having a pop at Stuart, and he's not the first to make the same errors. I've commended the K7000 and the signal injection/tracing method of fault finding for some years, and have built several myself. Three disappointed constructors have been in touch over time, due to non-working units, and when asked to email me a close-up pic of the completed PCB, for whatever reason, in each case, the resistors have been installed in the wrong order.

It's the sort of mistake we can all make and have done, and it can be very dispiriting, but it's a useful and positive learning exercise, which in the long run, helps us to avoid future pitfalls. It's also very uplifting to get something working when at first it failed to work. I guess that the perverse frisson of satisfaction that we derive from repairing duff stuff anyway!

Though the resistors supplied with the K7000 are the 'three band' type even so, colours can be confusing, so like most I guess, I always check the values before installing.

The good thing about the K7000 PCB is that the holes for component leads are 1mm so unsoldering is easy.

There are two minor shortcomings with the K7000. Namely:

1) Because the injector and tracer circuitry share the same small PCB and both are on at the same time rather than being independently switched, there is some 'breakthrough', that is that the injector tone can be heard in the background of the tracer speaker, but it's not a problem. (The injector could be independently switched by cutting the +ve supply to R5, R6 and T2 collector, but that would be too much of a faff).

2) Secondly, the volume control for the tracer (and maybe the level control for the injector?) should be log, but is linear. In practice that presents no difficulties. The injector level control is 4k7, and the tracer volume control is 47k, so there's potential to get those in the wrong place.

Well done to Stuart for sorting it, and neatly boxing it up. It will soon earn its keep.

All's well that ends well!
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Old 28th Oct 2018, 11:34 pm   #13
Stuartb
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Default Re: Velleman K7000 Not Working

Hi David,

Thanks for the tips I hope to use it soon.

Stuart
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Old 2nd Dec 2018, 11:49 pm   #14
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Default Re: Velleman K7000 Not Working

Good Post Paula K7000
I also followed the instruction and it didn't work , but followed your resistor guide and now it's working.

Thank you Ken
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Old 3rd Dec 2018, 1:19 pm   #15
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Default Re: Velleman K7000 Not Working

Over the years, I've not been alone in encouraging less experienced forum members to adopt a logical approach to fault diagnosis rather than to make assumptions. Methodical signal injecting and tracing is a useful method of pinpointing where faults may lie, and many restorers will have made their own injector/tracers for decades before Velleman came on the scene. Building the K7000 is an ideal way to gain experience in soldering, following and understanding a circuit, and going about things in a careful manner with attention to detail. The instructions that come with the kit are very comprehensive and if built as instructed, the device will work right way. The booklet is rather small and it's as well to download and print off the A4 sized instructions from the website.

Over time, I've help a number of disappointed disheartened builders who've built the kit and found that it hasn't worked. Every time it's been due to failure to follow the instructions on installing the parts - particularly the resistors - in the correct order. Velleman stress in large upper case print: 'AXIAL COMPONENTS ARE TAPED IN THE CORRECT MOUNTING SEQUENCE - REMOVE THEM FROM THE TAPE ONE AT A TIME!'

In each case when I've been asked for help (or when others have answered a plea for help in a thread) it's very evident what's gone wrong. When asked for a picture of the faulty board, it's noted from the colour bands on the resistors that the instructions haven't been followed and the resistors have just been taken off the bandolier on the assumption that they're in the order of R1, R2, R3 etc. That will be abundantly clear on Pic 1 below - a photo of a non-working PCB. I've annotated the picture with the list of correct values, alongside the way they were actually installed. As will be seen, the wrongly installed resistors number from 1 to 11 in reverse order, so as they've been removed from the bandolier, they were wrongly assumed to be in that order. When removed and refitted in the correct positions, the K7000 worked fine.

Fortunately, the PCB is very forgiving and the resistors can easily be unsoldered without damaging the PCB, and re-soldered into their correct positions. The easiest way to removed them (rather than a desoldering 'gun'), is by using clamping forceps on the resistor ends, melting the solder beneath the PCB and gently pulling the resistor out.

I should add that the forum member whose PCB features in pic1, was initially very disheartened, but having successfully re-built the PCB, went on to restore a non-working valve radio which had been seriously got at, modified and bodged by a previous owner. He had to first restore the set to how it was when it left the factory, then to diagnose and repair quite challenging faults, (using the K7000 as an aid), spending many hours and gaining much confidence in ending up with a working set. Flushed with success, he's gone on to other restorations.

Velleman use three-band colour coded resistors and state the colour bands of each one, but when building any equipment it's always a wise precaution to check anyway with a multimeter.

Pic 2 shows the three sections of the circuit, and some explanations might be of interest.

The Power Supply:

The K7000 can be powered either by a 7-0-7 or 9-0-9V transformer attached to points VA & VB, with it's centre '0' connected to ground, or by a 9V battery (PP3) to either VA/VB and ground. a 9V 'DC 'wallwart' could also be used. The two diodes will rectify the AC input, or if a battery or 'wallwart' is used, the diodes will guard against reverse polarity. (Rather a pity that the Roberts 'Revival' skimped on a reverse polarity diode). The 7V5 zener diode - 'ZD1' provides a 7.5V stabilised supply to the injector, though the supply to the amplifier section is unstabilised.

The Tracer Section:

This consists of a simple LM386 amplifier, with up to 0.5W output into an 8 Ohm speaker.

The Injector Section:

This provides a nice clean sinewave signal of approximately 1kHz (actual frequency unimportant), with adjustable amplitude up to 2.5V RMS. (See pic 3).

When signal tracing on valved equipment, where possible it's better to apply the probe to low voltage points - to the grid of an output valve for example, rather than to the anode of the previous valve. But nothing drastic will happen if you do apply the probe to a high voltage point as the input to the tracer and the output of the injector each have a 400V 100nF capacitor for protection. On the PCB layout, there are three holes for each of those capacitors, which might appear confusing. That's because Velleman at times use 1-- nF caps of a different physical size.

RV1 & RV2 look identical, but they have different values. RV1 - the injector output level control is 4k7, RV2, the tracer amplifier volume control, is 47K, so make sure they're in the correct position.


The kit only consists of the PCB and board mounted components. To finish it off you need a small 8 Ohm speaker (4 Ohms will do just as well), speaker grille, sockets for the tracer input/injector output (I use phono sockets), two knobs, an on/off switch and some sort of enclosure in which to house it - either ABS, metal (eg, die-cast of sheet aluminium) or wood. The box needs to be about 7.5 cms (6 inches) tall x 10cms (4 inches) wide x 7 cms (2.75 inches) deep or any convenient size larger than that. As the battery will quickly run down if left inadvertently switched on, its a good idea to add an LED and series limiting resistor. Ultrabright LEDs use very little current. You'll also need some hook-up wire and screened lead.

I've mentioned before that because the tracer and injector share the same small PCB and aren't individually switched, some 'breakthrough' of the injector will be heard in he background of the speaker, but that's no hardship.

I hope these rather wordy notes might encourage other forum members to build one of these useful inexpensive devices, and if they do, might also help them to avoid the pitfalls that others have fallen victim to. No-one seems to get the electrolytic caps the wrong way round, or the diodes, transistors or IC, so no dramas at the end of the day!
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