Kenwood Food Mixer - No Power - Mint Cond - Dead.

[hinekadon]

great skeptic and nomeat will be pleased with you efforts ,,well done don

[Skepticist]

That lack of voltage drop means the PIC is taking virtually no current like 0.5mA or less which makes the collapsing onboard power supply an ongoing mystery.

Also the sine waves on the resonator look strange to me - what is marked on the resonator? (should have it's frequency marked on it)
Looks like you have the timebase set to 0.2uS/Div and period of the wave is about 0.9 of a division so ~0.18uS which is around 5.6MHz
If it's 0.5uS/Div then it's about 2.2MHz

But the good news is the oscillator appears to be running and that PIC has a very low operating current (~200uA at those frequencies) and is potentially OK, it would seem at least.

[Skepticist]

Better re-calc for the resistors all in parallel so the overall resistance is 22/4 or 5.5 ohm instead of 22 ohm (2 in parallel in series with 2 in parallel)
That makes the PIC current 4 times as high so around 2mA so still very modest.

Just keep eliminating all the non-faulty components and eventually....

[Skepticist]

All the evidence so far is now pointing back to the power supply on the other PCB and the major source of impedance for that supply is the large 0.33uF 275V capacitor.

Maybe keep the 3 pin plug out and pull the white cable spade connectors to completely disconnect the PIC board and devise a test or 2 to check the load capacity of that power supply EG it should be able to light up a red LED in series with a 150 ohm resistor for starters which is about 20mA if the voltage holds up at 5V. If any noticeable drop in voltage try again with 330 ohm in series for about 10mA then go for 560 ohm in series for about 5mA.

Remember the active is the DC positive and the centre pin on the 3 pin connector is the DC negative so wire up the led/resistor, connect voltmeter etc with the AC off and and avoid touching anything when it's on. For safety I'd set the voltmeter to the highest DC range and reduce that when the power's on as required to get a sensible reading in order to complete the test without a blackened spot where the meter used to be (sometimes I get overly cautious

[loopyloo]

By the way, the resistors shown in post #60 are 2.2ohm, not 22ohm.

[Reschs]

Just stop mucking around and replace the capacitor.
They are a well known problem.
Make sure you use the correct type.

[hinekadon]

i would feel a lot better if you used a isolating transformer cos as it stands you may not finish the project and that would really piss me off

[Uncle Fester]

Also the sine waves on the resonator look strange to me - what is marked on the resonator? (should have it's frequency marked on it)
Looks like you have the timebase set to 0.2uS/Div and period of the wave is about 0.9 of a division so ~0.18uS which is around 5.6MHz
If it's 0.5uS/Div then it's about 2.2MHz

These resonators are typically 4 and 6MHz.
He didn't mention if he used a 1x or 10x probe, so if it was 1x he typically added 100pF parallel to it which could lower a 6MHz resonator to 5.6Mhz.


Great job GT, and good to know the PIC is ticking.

Could really only be the 0.33µ or that fat resistor behind it. Basically back to my post #17
Nothing wrong with mucking around, that is how you learn things.
Do the 150Ω load test and check the 5V voltage with your Fluke, it will be fine on Auto DC-Voltage range. It is designed for that. Never use the Ohms range on Voltages! I think you did that before(post #26).
Unfortunately the LED won't say much as modern LEDs glow quite bright even with less than 1mA.

[Skepticist]

By the way, the resistors shown in post #60 are 2.2ohm, not 22ohm.

Nicely noticed (had to zoom in to see that)
Seems it's a good thing there wasn't a short in that case with only 0.55 ohm in series - so the PIC circuit was drawing .01/.55=18mA without breaking a sweat. I'd put a lot of that down to all the pullup resistors IE peripherals.

[Uncle Fester]

i would feel a lot better if you used a isolating transformer cos as it stands you may not finish the project and that would really piss me off

GT... about that, have you tested your RCD breaker lately ?

...or you could just solder out the 0.33µ cap and measure it with your FLUKE.

[Skepticist]

These resonators are typically 4 and 6MHz.
He didn't mention if he used a 1x or 10x probe, so if it was 1x he typically added 100pF parallel to it which could lower a 6MHz resonator to 5.6Mhz.

I have some identical resonators here that are the same colour but they're 50MHz - the frequency is marked on them EG 50.00 but the printing is a bit on the faint side. 20Mhz is the max for 8 bit PICs though.

I think I recall that cap being measured earlier but in-circuit and it came up 0.31uF. Never encountered ESR problems with that type of cap but you never know till you test it. The 51 ohm resistor could have gone high but no signs of overheating there.

[Uncle Fester]

Went through my resonator box and found the blue ones mostly 4MHz but also 5.5MHz which was the audio carrier for analogue TV in some countries including Australia.
Cost probably next to nothing.

[Skepticist]

Your spares box is more resonant than mine - more organised too

[GT250]

Recap:
So you're saying that with the CRO's readings on the CLK pins, the PIC's (maybe), ok and maybe I don't need to replace that board?

I measured the yellow cap (near the Red connector), - in board - and it read 0.31Ω - so you want me to take it out and measure it. I might just get a new one. I'll see if Jaycar have them (scratch that, don't think so).
Nomeat, You want me to replace that Blue Resonator? near the A and N - what about that yellow Cap?

I'm back at work now. So I'll have to hunt around for a local (non Ebay), supplier when I have time.

Thank you to everyone, I really appreciate it and it was nice to use the CRO (first time in 3 years) - thanks nomeat.

[loopyloo]

C105 hasn't had a mention yet.

[hinekadon]

c 105,s purpose is to soften any back emf from the motor becoming to the pic volts as far as i can see ????

[Uncle Fester]

Recap:
So you're saying that with the CRO's readings on the CLK pins, the PIC's (maybe), ok and maybe I don't need to replace that board?

I measured the yellow cap (near the Red connector), - in board - and it read 0.31Ω - so you want me to take it out and measure it. I might just get a new one. I'll see if Jaycar have them (scratch that, don't think so).
Nomeat, You want me to replace that Blue Resonator? near the A and N - what about that yellow Cap?

I'm back at work now. So I'll have to hunt around for a local (non Ebay), supplier when I have time.

Thank you to everyone, I really appreciate it and it was nice to use the CRO (first time in 3 years) - thanks nomeat.

Surely you meant 0.31µF not Ω. On it's own that reading would be within tolerance and measurement error.
You need to solder out that big yellow cap because other components in circuit will give you wrong readings. Technically the other yellow cap (mains filter) could be parallel for the tester so a reading of 0.31µF would then be too low.
If you replace the cap you must watch out for the X2 specification and a minimum of 275VAC.

I never said anything about replacing the resonator. I just showed to Skepticist that a reading of roughly 5.6Mhz is quite probable.

We are relying on your measurements and that the 5V actually collapses when everything is plugged together and that you connected it correctly. So for now I don't see anything wrong with the PIC controller board.

If the soldered out CAP still reads 0.31µF and the resistor is OK we will have to check again under power.
Plug and solder everything back, hopefully you left the wires stumps on VSS and VDD on the PIC so you can connect your multimeter with croco-clips to them to measure the 5V, and don't have to touch anything after you power up the mains.
Just to be double clear, you are NOT connecting a 5V source, just plugging it all in and testing the 5V right on the PIC when mains is applied.

Do not connect or test anything else while mains is applied.

[Skepticist]

Yes the CRO results indicate the PIC is healthy and the external supply tests indicate the problem is not on board 1 so suspicion has shifted back to the power supply itself for the 5V supply collapsing on load.

The cap in question is the larger yellow cap next to CN206 and marked 0.33uF 275VAC. It's an 'X2' metallised polypropylene cap rated for mains voltage and is being used as the major part of a voltage divider exploiting its capacitive reactance as a heatless resistor so the value (0.33uF) is somewhat critical if you go for a replacement cap.

Xc=10^6/(2.Pi.F.C) Xc in ohms, C in uF so it's about 9.6 kOhms at 50Hz

Most definitely remove that cap and measure its capacitance because any shift in C affects the reactance.
Also measure that 51ohm 1W resistor (next to the cap) to ensure it hasn't gone high in value.

NOTE: You'll probably have to order in a replacement to get one of the same value, physical dimensions and lead spacing (so it will fit).

Also: check that small electrolytic near CN206 as well, although it's not showing any signs of stress it will affect the quality of that DC supply
And to be thorough about it all, there's a ceramic cap (100nF?) next to the zener which is in parallel with the electrolytic. Those are very robust but leave no stone unturned here

[Skepticist]

C105 hasn't had a mention yet.

C105 and R104 are a 'snubber' across the triac main terminals to soak up switching spikes - any failure of those 2 is likely to be dramatic

[loopyloo]

C105 and R104 are a 'snubber' across the triac main terminals to soak up switching spikes - any failure of those 2 is likely to be dramatic

Ah yes of course a triac.
I kept thinking it was a fet for some silly reason and that would put C105 on the gate. lol
Never mind. carry on.