Here is a list of all the postings Joseph Noci 1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Anyone good at fault finding with amplifiers here?|
I see that Dutch fellow did sort of as I asked you to do - gently heat the long tailed pair individually with a soldering iron - except he cooled them with a frozen pancake ....Ah well, whatever flaps your jack...
I am sure your problem is simply gain mismatches in the long tailed pair(s).
The math shows it, so why not. Just fiddled a bit with LTP's in LTSpice ( Linear Technologies, now Analog Devices) free version of Spice - just cause its easy, lazy and quick.. Playing with the gains, with large loop gains, give BIG offsets for small hfe deltas.
When will you get your tranny's?
What intrigues me is ( assuming the amp's original offset was 'good' ) what causes it to change? Unless the transistor is abused, over-voltaged, overheated, etc, hfe should not really change much in years, and in a matched pair, the changes should be similar in both. From the circuit values I've seen , typical of your amp, current levels and Vce are well under control, so no abuse there. Interesting. I also remember, many years ago when making accessory widgets for our 'band' , I made a white noise generator, feeding voltage controlled filters to generate ocean sounds..but, noise eluded the device, Thinking the device stuffed, I used the transistor tester to verify - The transistor was ok, with hfe around 370. So I took a cigarette lighter and heated the BC107 till it glowed .. after cooling, I tested it again, still ok..and hfe had changed to 368....!!..within measurement error...
But,boy, did it now make nice ocean sounds....
By the way, Neil, Your amp seems to have been a Maplin Kit in the late 1980's - the circuit and some descriptive comments are in Ian Hickman's book 'Analog Circuitry Explained' - published 1990.
Well, You are then very lucky in the UK...
Most of the Combo Amps, PA systems and Jam Amps I get to repair here are Peavey, Phonic, and ALTO.
They are considered quite good stuff, and they have shifted most of their classis amps to Class D ( Peavey lagging behind, thank goodness).
A typical 500W+500W amp from Phonic or ALTO cost approx £650.00 . A 'Digital' (class D) version costs around £900.00 . An analogue powered speaker ( Woofer/Sub with a Tweeter) of 400Watts is around £400.00 in 'analogue' and around £600.00 in class D.
When I chase for spares, the agents in South Africa always start there response with 'Ooo, thats a Digital Amp, quite pricey, spares are..', or words to the same effect!
And of course, the next Hate up the list is a class D amp WITH a switchmode powersupply...THAT the agents refer to as a FULLY Digital amp....
And the trend with the agents these days is to not keep component spares - for most of the mid-range power amps they keep a powers supply module and the amplifier module with the latter around 35% the cost of the complete unit..
The only thing to like about that technology is that at my age it's easier to carry up the stairs to the workshop..
And, as a radio ham, I hate them even more..The EMI many of these amps generate on the HF bands is terrible! The filtering is always done down to a cost, with lip service to the regulations..Some of them are dead quiet till you plug in the guitar or a microphone..
Bring back the good Mr Hood anyday!
I HATE class D amps - They are the worst to repair. Everything has to work for it to work - you cannot debug or diagnose sections, one big, miserable closed loop that makes things go bang if you open the loop at the wrong place.
And I don't consider them 'Hi-Fi'...
Well, there are not many transistors in that amp so when you swap the last one out, all will work...
I second Adrian's comment on the pot - esp since you said that there was a point where the output FETs got hot - they had to be turned on to some extent for that - if the pot is open frame, clean the track with a little methylated spirits while winding the pot back and forth two or three times. ( note its position and return it to that). The output FET's standing current should vary smoothly while adjusting the pot up or down SLIGHTLY...Beware excess current in the output!
If you have spares, replace them, but if you have time...Fit the originals back, verify the output offset voltage, and gently heat one of the transistors with the soldering iron - see what the offset voltage does. Try to do the same with the other transistor when the first has cooled again and see if the effect is similar - and opposite..
What is the amps age?
I think that's a good place to start Neil. I repaired a Hitachi amp - see schematic below - similar to yours , but with stages inverted, and the input long tailed pair had to be well matched - gain delta of 5 gave around hundred millivolts output offset. This amp has pots for offset adjustment, but setting the pot voltages for equal Vbe showed how close the matching had to be. Also,the input LTP in this amp were bonded together, with copper foil wrapped around - for thermal tracking.
As said above, unplugging the pre-amp does naught WRT C204 - not sure if you checked that cap. The other caps appear non-polarised, so unless old, paper wound types, they should not be any problem.
The key, as Simon said,is that under quiescent conditions, the voltage at TR201/2 collector should be close to mid-rail.
You should be able to check TR201/2 in circuit - the circuit is reasonably balanced in coupled impedances and comparative readings between the two should reveal large deltas. Try the usual ohms readings tween BE, BC, EC, with positive and negative polarities, and compare each transistor. ( discharge PSU caps PSC1/2 first).
If nothing reveals, you may need to remove each and check in your fancy tester..
OR - lift the leg of the mosfet end of R207 . Connect a resistor, value equal to R202, between TR202 base and ground ( midpoint of the PSU caps). On power, the voltage at the collectors of TR201/2 should now be equal and close to mid-rail.
I do the repairs for our local Hi-Fi/Sound system retailer here in Swakopmund and work on equipment of all conceivable types..From shebeens, disco's, restaurants, homes, Churches, Bands....And have followed many a garden path in the search for the fault, so what do I know...
Ok, presume you meant between TR202/3 base and emitter, not collector..
What are the voltages between the base/emitter of TR203/4?
Something fishy around TR201/2 I would think. A positive voltage on the output would tend to turn TR202 more 'off' ( via R207) and cause the voltage on TR202 collector to become more negative. It is more positive than the collector of TR201 so maybe the voltages between base and emitter of TR201/2 can show something more.
Also, C204 seems to be an electrolytic? It may have become leaky ( electrically). With no input to the amp, can you disconnevt one leg of C204 and see if the output voltage remains?
At the moment, TR203 is turned on harder than TR204, hence it's collector will be at lower potential than TR204.
Neil, could you measure between the bases of the the first pair (TR201/2) with your meter at lo-volt range (10v scale maybe) please, and then between each transistor base and emitter (TR201/2)
Edited By Joseph Noci 1 on 17/08/2019 21:32:11
|Thread: Metal Cutting Power Saw|
YouTube hacksaw videoThank You those with nice words re my little power hacksaw...Two reasons I made that machine, one being that it has been a project on the wish list for many years, and two, I have a bandsaw - see below, so there was always a reason to not get started on the hacksaw..
This is a pic from the front cover of the user handbook - my saw differs slightly - switch gear in a different place, etc.
This saw works very well, but although it delayed the start of the hacksaw, it also prompted it..I dislike changing blades on the bandsaw, and the saw never seems to have the correct blade in it! I often cut thin wall (2mm maybe) tubing and then there is a 10TPI blade in the machine for the last 100mm aluminium billet that was cut, etc.
I always find that the different TPI blades track differently, and so to get a square cut involves faffing about after changing a blade. The blade guides are very firmly set up ( I did machine the mating surfaces to get a better fit than the sloppy delivered article). The blade guide bearings are firm and snug against the blade, but when the blade opening is more than 180mm to 200mm, the blade flexes between the guides and tracks as it will.
My blades are 22mm wide and I guess about 0.7mm thick? not sure..
I allways cut wet ( with coolant) for material of a few square inches and more.
So, the hacksaw was pushed up the list. Now the hacksaw has a 24tpi blade in it all the time and is used for all the thin stuff - for which it is better suited anyway, as the thin stuff does not take so long in the hacksaw.
Here is a video of the hacksaw while being made and tested...
Edited By Joseph Noci 1 on 17/08/2019 21:16:57
Just make it Ron! You can still call it modelling - model it after a bigger one!
|Thread: Chosing a drill grinding attachment or machine|
The nicest drill grinder I used was an oldish Meteor - they are still being made I see, albeit new styles, etc, but they still work the same way. As Clive said, if you have to faff about each time, and good results are not easily repeatable, then the jig is not worth it really. All you are after is a sharp and decent cutting drill to do the job you are busy with - the interest in the sharp drill is not really in the journey to get there! I tried various makes and types and just gave up on them. The Meteor I used was in a toolroom, and so sadly not my own, but it was fantastic. Insert the drill bit in the long-collet chuck, flip the chuck with drill point up into the in-place microscope, align the drill edges with the cross hairs, set the drill point or tip against the reference, flip the holder over into the wheel and swing the holder across the wheel. Rotate the holder 180deg and repeat. Advance the holder to put on cut and repeat.
From fitting a 6mm drill in the collet, to a perfect cutting edge ( on a drill that was just blunt, not chipped) takes all of 30 to 40 seconds...putting a new edge on a 2mm drill took 20 seconds.
Problem lies in the price of those units..
I made a cutter/grinder, and then a 4 (or 6) facet jig/holder with a microscope viewer to set up the drill - It works very well, with perfectly repeatable results, but needs more settup faffing than I like. I did post about it, with many pictures, but have no idea how to link to it, and don't wish to clutter this thread with more guff..
Link to the Meteor ( present day) stuff:
|Thread: Karcher pressure washer|
I was wondering where the worth was in :
I know. They were definitely signs to the owner, but are they then symptoms when the owner posts them on here?!
Yeah... but that would be his symptoms (sadness, ennui, financial anguish...) not the washer's . But doubtless a case for compensation from kaarcher for the mental distress, especialy if he can claim to be a minority such as an investment banker with too much money and a coke habit.
And the various bits of similar ilk, to the chap trying to find some help with his pressure washer...So , yes, rather worthless...and the vocab seems quite apt.
And there the Forum Falls Foul of Flexiloquent Folk partaking in a Floccinaucinihilipilification process....
I have a large one, diesel fired to heat the water as well, when desired. It does (rather, 'did' ) not get much use, and that caused the problem. On mine the pump has 4 pistons affixed to a swashplate that the motor turns directly. That whole assembly is in oil. The pistons pass through a wall to the water side of things, with a rubber seal on both sides of the wall, one in oil, one in water then into ceramic pressure cylinders. When the pump stands for weeks, the water dries out in the chamber ( runs out, dries out, etc) and the next start the pistons run dry in the water jacket side rubber seal for a short while, and the seal wears out much sooner. Then the water is simply moved around inside the water chamber, from cylinder to cylinder, and nought exits the pressure valve - hard to explain the exact geometry, but sound seals are the key..
The vendors sells a kit which includes pistons, all seals, some 'O' rings, etc and it took maybe an hour to make like new. Now I use the machine much more often...
Edited By Joseph Noci 1 on 09/08/2019 12:04:37
|Thread: WM18 - Z Axis power feed|
No, not really. Its the width of the actual pulse that is of interest, but I think safely ignored with your other findings..The motor is just a little on the small side..A pity your are so far away - I have many steppers languishing and would be happy to donate! Problem is shipping from Namibia is twice, or more, the Ebay cost for 4NM motor!
You can always use that motor on the x axis now..
What do you mean by 'top end'? At high speed ( top end of) or top end of the column? Where on the column's height should make no difference, unless there is binding at the top and not lower down. You may need to do some setting up and move the axis only with the handwheel ( stepper mechanically disconnected) so you can feel if the movement is smooth up and down - I would suggest you try achieve that first, regardless of the torque of the chosen motor..
That motor should be able to move the axis downwards with repeatable ease and if not, there must be some binding somewhere.
The Oscilloscope - I would have liked to see the width of the step pulse from the PWM generator to the stepper driver - the driver normally requires a certain minimum width and nowhere can I find what the pulse width is of that PWM generator that you have. However, if this is a problem, it normally manifests as lost pulses, which may or may not be part of the problem you experience.
A larger stepper needed , I think...
Bit late to enter the fray, but...I do think a NEMA34 size would have been better, or at least a motor with maybe around 3 to 4NM torque. The problem is really overcoming the stiction in the system and will be worse on the up..
If you are willing to try a few things -
Does the motor turn on its own, disconnected from the leadscrew?
If so, loosen up the Z Gibs completely and try again, just to see if things move.
If not, let me know and we take it from there.
Do you have an oscilloscope?
Can you post a wiring diagram of how you connected the bits?
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