Aiwa MX-Z3300M receiver repair, no display, capacitors in series

[Chungalin]

This is a common fault in this amp model and others from Aiwa, same age. VFD display doesn't work. Everything else OK, if you can operate it blindly.

The culprit is C15 and C16. C15 is 47uF/50V and C16 is 33uF/50V, both electrolytic. They put two 50V caps in series to get a 100V cap, but this is as crappy as putting rectifier diodes in parallel to add current. It works for a time, but ends up unbalancing and one component is exposed to more voltage (case of capacitors in series) or to more current (case of diodes in parallel) than the other, exceding its maximum and failing prematurely.

I've repaired this receiver two times. 2008, 2012 and now. It lasts 4 years. Now I want to do something different. This means an equivalent 20uF/100V, not easy to get. Perhaps this is why original enginer splitted it in two.

I attach schematic fragment. Any smart idea?

[budm]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

It uses those caps to drop down the ACV feeding the rectifier/ dual Voltage linear regulators circuit to drop -70vdc down to -32V.
May be you can use this:
http://www.parts-express.com/22uf-10...citor--027-348
Or you can tap of the -42V to generate the needed regulated -32V.

[Chungalin]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

After removing both caps, the only one that’s failed is C16 (null capacity and huge ESR). C15 is apparently not bad.

When I’ve seen your link with 22uF/100V unpolarized cap I’ve had an idea: you’re right, ideally, this should have been an unpolarized cap.

I have two good Rubycon 33uF/100V caps. I’ve recalled when I searched some time ago how to make an unpolarized cap from two polarized. I’ve put one in C16 position, with same polarity as marked in PCB, and C15 with reversed polarity. Now both positive terminals are in contact. This acts as a 16uF/100V unpolarized cap. It works, as expected. Question is: will we talk again about this in four years?

[stj]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

that's interesting, i have an Aiwa unit at the back of the stack of busted stuff with a very weak display.
have to go pull it out for a fresh look.

[Chungalin]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

This no-display failure may affect other models, like MX-Z3200M, MX-Z9400M, etc. Any one that looks similar to attached pic (this is from another repair shop in Spain, not mine).

[stj]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

similar, but the one i have is about 3 times as tall and has double tapedecks at the bottom!!

[Tube_Dude]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

It uses those caps to drop down the ACV feeding the rectifier/ dual Voltage linear regulators circuit to drop -70vdc down to -32V.

Hi, Budm

Quite the opposite. These capacitors are part of a voltage doubler circuit working together with D15, D16 and C17. They turn the input 30 Volts AC in 70 Volts DC at the input of the pre-regulator transistor T15...

[budm]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

Hi, Budm

Quite the opposite. These capacitors are part of a voltage doubler circuit working together with D15, D16 and C17. They turn the input 30 Volts AC in 70 Volts DC at the input of the pre-regulator transistor T15...

Ah I see now, you are correct, the feeding Voltage is only 30VAC, I did not see the D16 earlier which is blocked by the red circle which is part of the Voltage doubler circuit. Thanks.
I still do not see why they need to convert the 30VAC to -70VDC to feed two series connected regulator transistors just to drop it down to -32V when they could have use 30VAC to produce the -42VDC and regulated it to the needed -32VDC.

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

This is a common fault in this amp model and others from Aiwa, same age. VFD display doesn’t work. Everything else OK, if you can operate it blindly.

The culprit is C15 and C16. C15 is 47uF/50V and C16 is 33uF/50V, both electrolytic. They put two 50V caps in series to get a 100V cap, but this is as crappy as putting rectifier diodes in parallel to add current. It works for a time, but ends up unbalancing and one component is exposed to more voltage (case of capacitors in series) or to more current (case of diodes in parallel) than the other, exceding its maximum and failing prematurely.

I’ve repaired this receiver two times. 2008, 2012 and now. It lasts 4 years. Now I want to do something different. This means an equivalent 20uF/100V, not easy to get. Perhaps this is why original enginer splitted it in two.

I attach schematic fragment. Any smart idea?

If a cap is in series they act as resistors do in parallel or vice a versa. http://www.allaboutcircuits.com/text...el-capacitors/ Sorry I read the Volts on the caps as uF.

[Tube_Dude]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

I still do not see why they need to convert the 30VAC to -70VDC to feed two series connected regulator transistors just to drop it down to -32V when they could have use 30VAC to produce the -42VDC and regulated it to the needed -32VDC.

Me too! Can't see any good reason for the extra expenditure...!

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

If these are electrolytic caps connected directly to AC voltage and there is a significant swing on them they will wear out fast. Better to replace them with non-electrolytic. It will be a much bigger cap. Or buy a bunch of the electrolytics and have a maintenance schedule to replace them.

[budm]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

https://en.wikipedia.org/wiki/Voltage_doubler
http://www.electronics-tutorials.ws/...r-circuit.html

https://en.wikipedia.org/wiki/Voltage_multiplier

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

https://en.wikipedia.org/wiki/Voltage_doubler
http://www.electronics-tutorials.ws/...r-circuit.html

https://en.wikipedia.org/wiki/Voltage_multiplier

Interestingly enough I see no + marking for electrolytics in any of the diagram on that site. Electrolytics do not like being charged and discharged. They can accept a low tolerance of this as one would see on the output side of a bridge rectifier. The input side would be another thing. When they reverse current through them as a discharge would do they are not made to operate in a reverse current mode. This is why there is a time limit on electrolytic caps.Where a non-electrolytic cap will last way longer. In the thread the person replaces these every 4 years which also attest to the problem.

[budm]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

The polarity of the caps (if polarized caps are used) will be based on if you want + output with ref to GND or Negative out put with ref to GND, so the polarity of the cap (lytic caps) and the direction of the diodes will have to be installed correctly. The cap is not exposed to reverse bias due to the diode is not conducting in one half of the cycle. You have to draw the charge and discharge path to visualize it.
The old PC power supply with 120/240V selector switch uses the same topology.

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

The polarity of the caps (if polarized caps are used) will be based on if you want + output with ref to GND or Negative out put with ref to GND, so the polarity of the cap (lytic caps) and the direction of the diodes will have to be installed correctly. The cap is not exposed to reverse bias due to the diode is not conducting in one half of the cycle. You have to draw the charge and discharge path to visualize it.
The old PC power supply with 120/240V selector switch uses the same topology.

I did not say reverse bias I said discharge. They do not like to discharge as the current has to go in the reverse direction. It does not have to have the cap having a reverse voltage between the positive and negative terminals to have reverse current. When the voltage on the cap goes from say a positive 10 Volts to a positive 8 volts in order for that cap to do that it will be exposed to a reverse current because it is a discharge state.

[budm]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

This one may have better explanation as to what happen in each half cycle of the AC and how the current flows in the circuit and how they are charged and discharged.
https://en.wikipedia.org/wiki/Voltage_multiplier

https://upload.wikimedia.org/wikiped...er_explain.png

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

This one may have better explanation as to what happen in each half cycle of the AC and how the current flows in the circuit and how they are charged and discharged.
https://en.wikipedia.org/wiki/Voltage_multiplier

https://upload.wikimedia.org/wikiped...er_explain.png

If you will look at this and see how the progression was made away from tying them directly to the Ac line that is allow to discharge the caps. In the Dickson charge pump they are not allow the discharge the caps stay at there potential as the diodes stop any reversing of current. In the stacking you can see a the first cap is in series with the rest of the circuits and is subjected to discharge.

Although some leakage current will go through the diode in the reverse direction but it will be tiny.

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

This one may have better explanation as to what happen in each half cycle of the AC and how the current flows in the circuit and how they are charged and discharged.
https://en.wikipedia.org/wiki/Voltage_multiplier

https://upload.wikimedia.org/wikiped...er_explain.png

Bud M I looked again at your reference I think there is a lot more finesse going on then what is explained.

[keeney123]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

ran out of time limit here is the rest
Bud M I looked again at your reference I think there is a lot more finesse going on then what is explained. So I read your first source fully understand the principle of a perfect circuit. However when they say this builds up in more than a few cycles. There is discharging and charging of capacitors in place. Which will cause some ripple and unlike a full wave rectifier which is making all the ripple in one direction both cycles are used in opposite directions so the ripple will be in both direction. The amount of this ripple will adversely affect a electrolytic cap, depending on the amount and the current strength behind it. These voltage multipliers are used in low current high resistance outputs so maybe in these conditions the electrolytics would not be as affected as much, however they will be affected. As I have said above it depends on those factor as how fast the cap wears out. Along with how often the circuit is turned off and on and the length of time the electronics have been on. Now, that I know this fully it will be in a couple of week and I will forget most of it. Thank BudM for your references.

[makissat]

Re: Aiwa MX-Z3300M receiver repair, no display, capacitors in series

Hello guys! I have the exact same problem that is shown in the following video

https://www.youtube.com/watch?v=spD4YjYrgcQ

I have already changed the capacitors C15 and C16 but the display still doesn't works. Any ideas please?