06-08-2011, 08:36 PM
Thanks for your kind words Colin - making the PCB was a small gesture to repay all the help that you've given me, which is what the forum is all about I guess. Without your help and encouragement, my little Lorch lathe would still be a rusty heap, languishing neglected under the bench where it's been for the last five years!
Glad to hear that the ESR meter is now behaving itself. In the ones that I've built, I've used the metal cased 2N2222A transistor, and though I explained the pinouts and provided a diagram of the plastic ones that some constructors have used, I didn't build one using a plastic cased transistor to show the correct orientation on the PCB.
However, I've now made a couple of mods to the PCB layout based on feedback.
Firstly, though I know of no cases of the voltage regulator misbehaving, nevertheless, it's good practice to include a cap on the input side of the regulator, as forum member 'MartyB' pointed out recently. This can easily be done as a retro mod, simply by drilling through the +VE track and the ground track on the input to the regulator with a 0.8mm drill, and soldering a 0.1uF cap across the tracks, or more simply, to add the cap underneath the PCB, soldered on the two tracks. However, I suspect that most who have built the meter and found that it works well, will want to leave it alone! On the amended PCB, I've added a couple of pads for this addtional cap.
Secondly, it's become common practice of most magazine projects - Everyday Practical Electronics, 'Silicon Chip' etc (from whence, many EPE designs originate, in Oz), to include what's often unkindly referred to as an 'idiot diode'. This prevents damage or destruction of equipment due to inadvertent reversal of polarity. I know that a lot of contructors prefer to power bits of test gear with 'wall warts' rather than to fit batteries in everything, but personally, with something like an ESR meter, which is used only intermittently, and then only for a few minutes at most, I just use a cheapo PP3.
The problem with wall warts is that there's no one convention as to whther the centre pin is +VE or 0VE. Thus, it's easy to inadvertently apply reversed polarity to equipment. Some manufacturers recognise this risk and fit a reverse protection diode - others don't. With 1N4001s costing only a penny or two, at least if we home-brew, we can build things up to a standard - not down to a price, so I've amended the track to allow a protection diode to be fitted on the input to the voltage regulator. When I've etched and built a PCB up and tested it to confirm these mods are satisfactory, I'll post the amendments on the forum, with updated artwork, and an annotated layout showing all of the mods from the original version. I'll also use a plastic transistor and post a photo of a made up PCB to show the correct orientation.
As an aside, while writing on the topic of protection diodes, my son has several Roberts Revivals, which look presentable enough on the outside and have sold well - indeed, they've been such a money spinner that they revived the company's fortunes. But on closer inspection, they're really quite tatty inside, with their poorly put together MDF cabinet and puny speaker, and worse still, they have no reverse polarity protection. Personally, I think this is dire on a radio that's touted as a quality product at a ludicrously high price. Robert's 'get-out' when a radio is smoked due to polarity reversal will be in their instructions - 'always use the correct power supply'. My son always does, but indvertently plugged in the wrong lead - one that serves his i-pod docking station, next to his Revival. A puff of smoke, and that was it.
Not holding out much hope, I said I'd have a poke around, but found that the Revival PCB is unrecognisable as a radio at all. It has no IFTS no oscilator coil, no transistors and only three ICs - one is the audio chip, another takes care of AM, and the other, FM. The audio chip was clearly burnt to blazes, and an electrolytic cap with it. The chip is now obsolete, but I managed to get one quite cheaply from the States. That restored the radio on FM, but the AM chip was also jiggered - two rows of 28 pins! He never uses the radio on AM, so he was content with that, and I decided to quit while I was winning.
Roberts have always had this propensity to do quirky things - the ghaslty Mullard Modules, the TAD100 IC, and now this malarky. There's a saying in Yorkshire - 'all fur coat, but no knickers' - a term of disdain for those who haughtily put on airs and graces, (Think Hyancynth Bouquet!). In more polite circles, the term that tends to be used is 'mutton dressed up as lamb'. I'd say that leaving a 1p diode out of a £150 radio fits either description nicely. Nothing at all to do with ESR meters - just an example of what happens when a simple protection device isn't fitted.
Rant over.
If anyone on the forum decides to have a go at building the ESR meter, if they get stuck and can't get it to work, I'll be happy to help. The layout is uncritcal - it can be built on stripboard as well as a PCB. For anyone who has a scope, it makes a nice project to get to know how to use the scope.
It has to be said that for valve radio restoration, an ESR meter has little application. Most valve radio only have three electrolytic caps - two for smoothing, and one for the cathode bypass in the audio stage - as often as not, a 25uF 25V, which I routinely replace as they're almost always shot.
However, transistor radios often use several small electrolytic caps, and given their age (R200s, TR82s etc) they will often have a high ESR. They may not stop the radio from working, but they will degrade its performance. On the other hand, when checked on an ESR meter they ma be fine, so can be left in place, rather than to do as we tend to with waxy caps in valve radios and pull them out, come what may.
David
Glad to hear that the ESR meter is now behaving itself. In the ones that I've built, I've used the metal cased 2N2222A transistor, and though I explained the pinouts and provided a diagram of the plastic ones that some constructors have used, I didn't build one using a plastic cased transistor to show the correct orientation on the PCB.
However, I've now made a couple of mods to the PCB layout based on feedback.
Firstly, though I know of no cases of the voltage regulator misbehaving, nevertheless, it's good practice to include a cap on the input side of the regulator, as forum member 'MartyB' pointed out recently. This can easily be done as a retro mod, simply by drilling through the +VE track and the ground track on the input to the regulator with a 0.8mm drill, and soldering a 0.1uF cap across the tracks, or more simply, to add the cap underneath the PCB, soldered on the two tracks. However, I suspect that most who have built the meter and found that it works well, will want to leave it alone! On the amended PCB, I've added a couple of pads for this addtional cap.
Secondly, it's become common practice of most magazine projects - Everyday Practical Electronics, 'Silicon Chip' etc (from whence, many EPE designs originate, in Oz), to include what's often unkindly referred to as an 'idiot diode'. This prevents damage or destruction of equipment due to inadvertent reversal of polarity. I know that a lot of contructors prefer to power bits of test gear with 'wall warts' rather than to fit batteries in everything, but personally, with something like an ESR meter, which is used only intermittently, and then only for a few minutes at most, I just use a cheapo PP3.
The problem with wall warts is that there's no one convention as to whther the centre pin is +VE or 0VE. Thus, it's easy to inadvertently apply reversed polarity to equipment. Some manufacturers recognise this risk and fit a reverse protection diode - others don't. With 1N4001s costing only a penny or two, at least if we home-brew, we can build things up to a standard - not down to a price, so I've amended the track to allow a protection diode to be fitted on the input to the voltage regulator. When I've etched and built a PCB up and tested it to confirm these mods are satisfactory, I'll post the amendments on the forum, with updated artwork, and an annotated layout showing all of the mods from the original version. I'll also use a plastic transistor and post a photo of a made up PCB to show the correct orientation.
As an aside, while writing on the topic of protection diodes, my son has several Roberts Revivals, which look presentable enough on the outside and have sold well - indeed, they've been such a money spinner that they revived the company's fortunes. But on closer inspection, they're really quite tatty inside, with their poorly put together MDF cabinet and puny speaker, and worse still, they have no reverse polarity protection. Personally, I think this is dire on a radio that's touted as a quality product at a ludicrously high price. Robert's 'get-out' when a radio is smoked due to polarity reversal will be in their instructions - 'always use the correct power supply'. My son always does, but indvertently plugged in the wrong lead - one that serves his i-pod docking station, next to his Revival. A puff of smoke, and that was it.
Not holding out much hope, I said I'd have a poke around, but found that the Revival PCB is unrecognisable as a radio at all. It has no IFTS no oscilator coil, no transistors and only three ICs - one is the audio chip, another takes care of AM, and the other, FM. The audio chip was clearly burnt to blazes, and an electrolytic cap with it. The chip is now obsolete, but I managed to get one quite cheaply from the States. That restored the radio on FM, but the AM chip was also jiggered - two rows of 28 pins! He never uses the radio on AM, so he was content with that, and I decided to quit while I was winning.
Roberts have always had this propensity to do quirky things - the ghaslty Mullard Modules, the TAD100 IC, and now this malarky. There's a saying in Yorkshire - 'all fur coat, but no knickers' - a term of disdain for those who haughtily put on airs and graces, (Think Hyancynth Bouquet!). In more polite circles, the term that tends to be used is 'mutton dressed up as lamb'. I'd say that leaving a 1p diode out of a £150 radio fits either description nicely. Nothing at all to do with ESR meters - just an example of what happens when a simple protection device isn't fitted.
Rant over.
If anyone on the forum decides to have a go at building the ESR meter, if they get stuck and can't get it to work, I'll be happy to help. The layout is uncritcal - it can be built on stripboard as well as a PCB. For anyone who has a scope, it makes a nice project to get to know how to use the scope.
It has to be said that for valve radio restoration, an ESR meter has little application. Most valve radio only have three electrolytic caps - two for smoothing, and one for the cathode bypass in the audio stage - as often as not, a 25uF 25V, which I routinely replace as they're almost always shot.
However, transistor radios often use several small electrolytic caps, and given their age (R200s, TR82s etc) they will often have a high ESR. They may not stop the radio from working, but they will degrade its performance. On the other hand, when checked on an ESR meter they ma be fine, so can be left in place, rather than to do as we tend to with waxy caps in valve radios and pull them out, come what may.
David
