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engr
11-29-2020, 04:14 AM
Hello, I own a KM Bizhub C308. The unit was built in 2018. From what I can tell, the unit performs perfectly. However, the power supply exhibits the "humming" described by other folks on similar Bizhub printers. I've tested the electronics using clamp meters, a DMM, and a digital scope. The power is being drawn by the fuser power circuit. This section of the PSU has a triac and a series inductor coil to power the fuser heaters. The individual heater lamps are approximately 1.4 ohm and 2.5 ohm. I don't have access to any specifications, so I'm hoping they are testing okay. At those impedance levels, I see why the current is drawing so hard. I see a spike every 5 seconds to about 13A. Without the inductor, the initial current would probably be around 80A! I can understand the point of keeping the fuser hot while in ready mode, but I don't see the point of a triac if we're simply turning the fuser on/off. It's a solid state switch, but it can also throttle the heat and avoid the need to turn on/off. It would likely be easier on the fuser too.

The current draw seems excessive. The lights dim and the unit makes a disruptive humming sound that is causing problems for our users.

I have two questions. 1.) is this normal for a c308 to cycle the fuser on/off like this while in the "ready" state? 2.) what can be done to mitigate the large rush of current to the printer? Do later firmware mitigate this situation by throttling the triac a little to avoid the current spike?

allan
11-29-2020, 06:40 AM
Try changing the fuser temp control mode in service. Think there are like 4 different modes.

allan
11-29-2020, 06:45 AM
47443

Ok so not modes but phase control levels.
Bad image but look for it in the manual.
Describes the issue you have, its noise thrown back from the phase control that can be changed.
Depends i guess if you are on 50 or 60Hz.

engr
11-29-2020, 07:01 AM
Thank you @allan for your response. I cannot really read the image from the manual you posted and I searched the manuals I have access to for the heater modes, but can't find anything. I know exactly what you're talking about and I did try changing these in service mode. I didn't notice any difference, but I didn't really understand what each mode did. It would sure be nice if KM would explain each setting in their software.

Being on 60 hz, I suppose I my setting might be different, but the machine has always been configured for 60 hz. The noise is only part of the problem. I can probably quiet the coil by gluing the windings. More of the problem is the lights near the office dim when the printer pulls heat (every 5 sec).


47443

Ok so not modes but phase control levels.
Bad image but look for it in the manual.
Describes the issue you have, its noise thrown back from the phase control that can be changed.
Depends i guess if you are on 50 or 60Hz.

allan
11-29-2020, 07:35 AM
Thank you @allan for your response. I cannot really read the image from the manual you posted and I searched the manuals I have access to for the heater modes, but can't find anything. I know exactly what you're talking about and I did try changing these in service mode. I didn't notice any difference, but I didn't really understand what each mode did. It would sure be nice if KM would explain each setting in their software.

Being on 60 hz, I suppose I my setting might be different, but the machine has always been configured for 60 hz. The noise is only part of the problem. I can probably quiet the coil by gluing the windings. More of the problem is the lights near the office dim when the printer pulls heat (every 5 sec).

Florescent lights?

tsbservice
11-29-2020, 09:46 AM
When the fluorescent light flickers you should go down the levels and when there is a noise at power source system turn up the level.
It's in service mode --> Machine --> Heater control level

blackcat4866
11-29-2020, 03:39 PM
It's entirely normal for fuser heaters to turn On in pulses at 60Hz intervals (in the US).

The way I understand the theory, when the AC voltage passes through the zero volt axis (or zero-cross) the heater is pulsed on so that it draws the minimum amount of watts. Some machines (specifically Kyocera, maybe others) can identify variations in the frequency. The idea is that the heater control circuitry must be able to anticipate the next zero-cross to pulse on the heater. If the zero-cross does not happen when anticipated the MFP can draw significantly more watts. Kyoceras will trigger a zero-cross error ... meaning that the AC frequency varied too much.

All that being said, humming has been an ongoing issue with certain models. There was a Canon with particularly noisy power supplies. When I ordered a replacement sometimes the power supply was quieter, sometimes louder. Sometimes putting that same noisy power supply in a different machine made it quieter. The amount of hum never affected its ability to power the machine.

If you can live with the noise, I recommend doing nothing.
=^..^=

BillyCarpenter
11-29-2020, 03:47 PM
It's entirely normal for fuser heaters to turn On in pulses at 60Hz intervals (in the US).

The way I understand the theory, when the AC voltage passes through the zero volt axis (or zero-cross) the heater is pulsed on so that it draws the minimum amount of watts. Some machines (specifically Kyocera, maybe others) can identify variations in the frequency. The idea is that the heater control circuitry must be able to anticipate the next zero-cross to pulse on the heater. If the zero-cross does not happen when anticipated the MFP can draw significantly more watts. Kyoceras will trigger a zero-cross error ... meaning that the AC frequency varied too much.

All that being said, humming has been an ongoing issue with certain models. There was a Canon with particularly noisy power supplies. When I ordered a replacement sometimes the power supply was quieter, sometimes louder. Sometimes putting that same noisy power supply in a different machine made it quieter. The amount of hum never affected its ability to power the machine.

If you can live with the noise, I recommend doing nothing.
=^..^=

That's interesting but I don't understand why 60hz crossing the 0-threshold has anything to do with anything. In the USA most things run on 120vac at 60hz. So, the Ac sine wave goes up +60vac, goes down -60vac and that's equals 120vac. And it does that 60 times per second and that = 60hz.

blackcat4866
11-29-2020, 04:03 PM
That's interesting but I don't understand why 60hz crossing the 0-threshold has anything to do with anything. In the USA most things run on 120vac at 60hz. So, the Ac sine wave goes up +60vac, goes down -60vac and that's equals 120vac. And it does that 60 times per second and that = 60hz.

Alright, try this:
V=IR. When V=~0 momentary, 0/R=I or ~0 amps


P=IV. When I=~0 and V=~0, then P=~0 watts momentary. In practice it's never 0 watts, but you get the idea.

skynet
11-29-2020, 04:14 PM
So, the Ac sine wave goes up +60vac, goes down -60vac and that's equals 120vac. And it does that 60 times per second and that = 60hz.

Not quite, it rises to +120volts and decends to -120volts

BillyCarpenter
11-29-2020, 04:16 PM
Alright, try this:
V=IR. When V=~0, 0/R=I or ~0 amps


P=IV. When I=~0 and V=~0, then P=~0 watts. In practice it's never 0 watts, but you get the idea.

I suppose technically you are correct that the fuser lamp pulses on and off at 60hz. But the same is true for the ordinary light bulb. The only problem is that it does it so fast that the human eye can't see it. As far as when a fuser lamp (or light bulb) draws the most power during the AC sine wave? Well, I agree it's never zero and to explain any further would require going into RMS power measurements. :p

blackcat4866
11-29-2020, 04:29 PM
I suppose technically you are correct that the fuser lamp pulses on and off at 60hz. But the same is true for the ordinary light bulb. The only problem is that it does it so fast that the human eye can't see it. As far as when a fuser lamp (or light bulb) draws the most power during the AC sine wave? Well, I agree it's never zero and to explain any further would require going into RMS power measurements. :p

The light bulb is constantly connected and it's intensity varies similar to that same sine wave. The fuser heater has driver circuitry to pulse ON only at the zero-cross.

BillyCarpenter
11-29-2020, 04:35 PM
The light bulb is constantly connected and it's intensity varies similar to that same sine wave. The fuser heater has driver circuitry to pulse ON only at the zero-cross.


I see said the blind man. I didn't know that. My bad.

I haven't really studied this stuff on the newer models. That didn't used to be the case back in the day and I suppose there's a reason some engineer came up with it but at the end of the day I can't think of a good reason. I suppose maybe it helps keep the fuser at a more consistent temp. Then again, engineers sometimes just want to be different.

blackcat4866
11-29-2020, 04:47 PM
I think the goal is to reduce energy usage and mechanical noise. It's the same reason that copiers now have 20 or more DC motors <1 amp, and turns them ON only as needed, rather than one 8 amp AC motor that runs continuously at the same speed during the whole copy process. =^..^=

BillyCarpenter
11-29-2020, 04:48 PM
If I remember correctly, and it's been a while....

Back in the day on the Sharp copiers the fuser circuitry was fairly simple. A triac would receive a gate signal from the fuser circuit and the lamp was either on or off and that was controlled by the thermistor. Interesting discussion. Things have changed. I should have known. lol

BillyCarpenter
11-29-2020, 05:01 PM
I think the goal is to reduce energy usage and mechanical noise. It's the same reason that copiers now have 20 or more DC motors <1 amp, and turns them ON only as needed, rather than one 8 amp AC motor that runs continuously at the same speed during the whole copy process. =^..^=


That's an excellent analogy. Point well taken.

blackcat4866
11-29-2020, 05:03 PM
Correct. And we saw plenty of bad triacs. I got to learn that lesson on a Mita DC-152Z that came incorrectly wired from the factory. Essentially the heat lamp was ON all the time. The first few times we waited until the thermostat blew. The heat roller warped like a banana each time.

This machine got parted out then reassembled several times until one day, scrutinizing the manual, I got the bold (perhaps stupid ...) idea to swap the spade terminals on the triac. Now the fifth or maybe sixth heat roller ... it warmed up normally after almost a year. =^..^=

Sorry, now way way off topic.

BillyCarpenter
11-29-2020, 05:10 PM
Correct. And we saw plenty of bad triacs. I got to learn that lesson on a Mita DC-152Z that came incorrectly wired from the factory. Essentially the heat lamp was ON all the time. The first few times we waited until the thermostat blew. The heat roller warped like a banana each time.

This machine got parted out then reassembled several times until one day, scrutinizing the manual, I got the bold (perhaps stupid ...) idea to swap the spade terminals on the triac. Now the fifth or maybe sixth heat roller ... it warmed up normally after almost a year. =^..^=


I've seen a few fusers go into meltdown because of a shorted triac. Major fire hazard.

engr
11-29-2020, 05:28 PM
Thank you both for your replies. The reason power is switched at the zero cross is to avoid burning up the triac (which is used to switch the power on/off). It's easier, and creates less heat, to switch on a load that's unloaded. Essentially the triac creates a form of Pulse Width Modulated (PWM) A/C to the inductive coil powering the resistive heater element. Technically speaking, the voltage does not alternate between +/- 60V or +/- 120V, it alternates between 120*sqrt(2) or 169.7V. We just use the Root Mean Square of the peak when we refer to AC voltage. You guys probably already know that, but I just wanted to make sure we're on the same page.

What I think I'm hearing as far as the humming is the inductor windings physically moving. I think stabilizing those will help. It appears the triac commands a pulse to the inductor coil which then releases it's energy (DC) into the resistive fuser heating element. I don't know if the current spike is normal because I don't have any information about the power board/pcb.

I will tinker with the heat selector value. Where can I find a service manual that tells me what each value does? Are there circuit diagrams and other technical information that would help me understand if the operation is normal? I don't have all the manuals.

Oh, there was a comment about my lights. I have LED lights in the office. Yes, they are sensitive to line loads.

Thank you.

BillyCarpenter
11-29-2020, 05:36 PM
Not quite, it rises to +120volts and decends to -120volts


Actually, it's about +170vac on the upper peak and -170vac on the lower peak if you look at it on an o-scope. On a volt meter it will read 120vac because it uses RMS value. (60v upper peak and 60v lower peak using volt meter.)



https://www.youtube.com/watch?v=vOh2OSJ44eE

BillyCarpenter
11-29-2020, 05:41 PM
Thank you both for your replies. The reason power is switched at the zero cross is to avoid burning up the triac (which is used to switch the power on/off). It's easier, and creates less heat, to switch on a load that's unloaded. Essentially the triac creates a form of Pulse Width Modulated (PWM) A/C to the inductive coil powering the resistive heater element. Technically speaking, the voltage does not alternate between +/- 60V or +/- 120V, it alternates between 120*sqrt(2) or 169.7V. We just use the Root Mean Square of the peak when we refer to AC voltage. You guys probably already know that, but I just wanted to make sure we're on the same page.

What I think I'm hearing as far as the humming is the inductor windings physically moving. I think stabilizing those will help. It appears the triac commands a pulse to the inductor coil which then releases it's energy (DC) into the resistive fuser heating element. I don't know if the current spike is normal because I don't have any information about the power board/pcb.

I will tinker with the heat selector value. Where can I find a service manual that tells me what each value does? Are there circuit diagrams and other technical information that would help me understand if the operation is normal? I don't have all the manuals.

Oh, there was a comment about my lights. I have LED lights in the office. Yes, they are sensitive to line loads.

Thank you.

Good stuff. I was thinking any humming noise is usually generated by an inductor or transformer.

BillyCarpenter
11-29-2020, 05:53 PM
Thank you both for your replies. The reason power is switched at the zero cross is to avoid burning up the triac (which is used to switch the power on/off). It's easier, and creates less heat, to switch on a load that's unloaded. Essentially the triac creates a form of Pulse Width Modulated (PWM) A/C to the inductive coil powering the resistive heater element. Technically speaking, the voltage does not alternate between +/- 60V or +/- 120V, it alternates between 120*sqrt(2) or 169.7V. We just use the Root Mean Square of the peak when we refer to AC voltage. You guys probably already know that, but I just wanted to make sure we're on the same page.

What I think I'm hearing as far as the humming is the inductor windings physically moving. I think stabilizing those will help. It appears the triac commands a pulse to the inductor coil which then releases it's energy (DC) into the resistive fuser heating element. I don't know if the current spike is normal because I don't have any information about the power board/pcb.

I will tinker with the heat selector value. Where can I find a service manual that tells me what each value does? Are there circuit diagrams and other technical information that would help me understand if the operation is normal? I don't have all the manuals.

Oh, there was a comment about my lights. I have LED lights in the office. Yes, they are sensitive to line loads.

Thank you.

By the way, what is your background? You sound like an engineer?

engr
11-29-2020, 06:00 PM
@Billy, you would be correct sir. I am an aerospace engineer who happens to have dabbled in electronics for the last 30 years :)~ We removed the Sony power board from this machine for inspection and found it is extremely well built. Top quality capacitors (Rubycon) and the board layout is made for serviceability. Actually the whole machine seems to be well built. We found nothing wrong with the board aside from the noise. I am going to try strapping the coils to see if I detect any change in the noise.

Do you or anyone else have access to some of these manuals that might help me further? I'm kind of flying blind right now. Service manuals and circuit diagrams would help me understand this better.

Thank you!

BillyCarpenter
11-29-2020, 06:15 PM
@Billy, you would be correct sir. I am an aerospace engineer who happens to have dabbled in electronics for the last 30 years :)~ We removed the Sony power board from this machine for inspection and found it is extremely well built. Top quality capacitors (Rubycon) and the board layout is made for serviceability. Actually the whole machine seems to be well built. We found nothing wrong with the board aside from the noise. I am going to try strapping the coils to see if I detect any change in the noise.

Do you or anyone else have access to some of these manuals that might help me further? I'm kind of flying blind right now. Service manuals and circuit diagrams would help me understand this better.

Thank you!

I don't work on this brand or I would be glad to send you the manual. I'm sure someone will help you out. Thanks for the education, tho. ;)

blackcat4866
11-29-2020, 06:30 PM
I'll share what we're provided ... which is to say not much. It's been over a decade since we got actual circuit breakdowns. The most you can hope for is pinouts and signal names.

engr
11-29-2020, 06:58 PM
@Blackcat, thank you for that! It's at least more data than I had before.

Yeah, I'm disappointed how much of a "disposable" world we're now living in. The solution always seems to be to replace the part when it could be easily repaired if information was given. I wonder what the chances are that I could get a Minolta engineer on the phone and obtain a schematic of the board? Sometimes we get lucky.

tsbservice
11-29-2020, 07:07 PM
@Blackcat, thank you for that! It's at least more data than I had before.

Yeah, I'm disappointed how much of a "disposable" world we're now living in. The solution always seems to be to replace the part when it could be easily repaired if information was given. I wonder what the chances are that I could get a Minolta engineer on the phone and obtain a schematic of the board? Sometimes we get lucky.

I agree with you. But chances are slim, I doubt even KM direct in USA have them. Maybe if some HYTEC engineer is member of this forum he could help.

blackcat4866
11-29-2020, 07:16 PM
I agree with you. But chances are slim, I doubt even KM direct in USA have them. Maybe if some HYTEC engineer is member of this forum he could help.

That's a good idea! Hytec repairs the boards ... maybe they get more resources than we get.

Factory Authorized Circuit Board Repair by Hytec Dealer Services, Inc. (https://www.hytecrepair.com/)
=^..^=

BillyCarpenter
11-29-2020, 07:27 PM
That's a good idea! Hytec repairs the boards ... maybe they get more resources than we get.

Factory Authorized Circuit Board Repair by Hytec Dealer Services, Inc. (https://www.hytecrepair.com/)
=^..^=

I'm sure they do. I've spoken with Hytec techs on the phone many times but I've never asked them for any schematics. I'm thinking they probably wouldn't release that info as there's no money in that for them. Same for Ricoh. There's just no money it it for them.


Of KM or whomever.

copier tech
11-29-2020, 08:13 PM
@Blackcat, thank you for that! It's at least more data than I had before.

Yeah, I'm disappointed how much of a "disposable" world we're now living in. The solution always seems to be to replace the part when it could be easily repaired if information was given. I wonder what the chances are that I could get a Minolta engineer on the phone and obtain a schematic of the board? Sometimes we get lucky.


Its all about safety now, back in the day I would carry a soldering iron & use it most days, however not today not used it in years.

All manufactures don't want to 'allow' us to repair these boards & risk causing a fire & create a law suit!

engr
11-30-2020, 04:22 AM
I can understand the perceived safety in a company withholding technical info, but I'm not sure if that really helps the company in the long run. Good techs may actually help the company figure out issues in the field and improve the product. Some of the best and most revered product lines have extensive support data out there. When the product is a decade old with no data or knowledge base, no one wants to take the risk so the product fizzles. Maybe that's the goal. But, for companies touting "eco friendly" and marketing such innovative features, it seems a counterproductive to be so remove/replace centered. They could make just as much selling OEM replacement parts for decades and providing schematics. Sorry to get on my soap box. I'll leave you with a video that explains my frustration.

The right to repair movement - YouTube (https://youtu.be/tr3nZpNHWnw)

allan
11-30-2020, 07:22 PM
The manual contains schematics point to point wiring. Konica Minolta does not publish the diagrams thru there channels. Been repairing boards here and there. Been struggling with the power boars the control boards are much easier for me. If you know the diagnostics code it had on it you have a solid place to start looking. Kinda like the way the buzzing sounds.

Yea the electronics on these machines are top of the range stuff. Been amazed at how some of these machines go for 20 years plus of service.
I like tinkering with electronics by no means an engineer. Built a CNC plotter from printer parts that scribes off blue dykem 5 microns a pass. Used that to make motor driver PCB's with the driver chips from a copier for the NEMA 17 motors found in a document feeder. Fun stuff. Some PSU are easy to switch on only need a constant load from startup so just add a power resistor of the correct value.

So what is the plan hot glue? Silicone?

engr
11-30-2020, 11:13 PM
Allan, I've heard chokes make noises like this before and I usually start with a rubber band around it to see if it changes. Then hot glue is my go-to. I tried a rubber band with no difference. I ran out of time so I'll have to come back around to it later. I'll try gluing it, but it may eventually just get replaced (the inductor that is). The problem is I think it's part of a tank circuit which means the inductance value needs to be spot on to work right. It would be easier to just have a part number or value. I'll look closer. Here's the inductor I'm after.

47460

blackcat4866
11-30-2020, 11:43 PM
Please let us know of your progress. =^..^=

tulintron
12-01-2020, 08:18 PM
Allan, I've heard chokes make noises like this before and I usually start with a rubber band around it to see if it changes. Then hot glue is my go-to. I tried a rubber band with no difference. I ran out of time so I'll have to come back around to it later. I'll try gluing it, but it may eventually just get replaced (the inductor that is). The problem is I think it's part of a tank circuit which means the inductance value needs to be spot on to work right. It would be easier to just have a part number or value. I'll look closer. Here's the inductor I'm after.

47460Engr and all folks, good afternoon.I'm sorry for the English, because I'm Brazilian.


I also love electronics and I found the comments on this topic sensational.


I managed to cause a hum in the power supply, replacing only the drum in the unit, for a drum in line 4.
Internally I don't know the difference because I don't have one from line 8 to open. But when I remove the drum from line 4 and return with the drum from line 8, the buzz at the source simply disappears.

engr
12-01-2020, 08:27 PM
Tulintron, that's interesting. I'm not sure what line 4 and 8 are, but it's interesting that the drum can affect the power supply noise.

Do you guys know what the resistance across the fuser heating element should be? When I first checked it, I thought it was incredibly low, but after disassembling, I don't find anything that looks out of whack. One element was about 2.5 ohm, the other was maybe 1.5 ohm. That's a lot of current!

tsbservice
12-01-2020, 08:28 PM
Engr and all folks, good afternoon.I'm sorry for the English, because I'm Brazilian.


I also love electronics and I found the comments on this topic sensational.


I managed to cause a hum in the power supply, replacing only the drum in the unit, for a drum in line 4.
Internally I don't know the difference because I don't have one from line 8 to open. But when I remove the drum from line 4 and return with the drum from line 8, the buzz at the source simply disappears.

tulintron very interesting but as usual I expect that from you.
You mean you only swapped cylinders and that cures humming?
Take care buddy.

allan
12-01-2020, 08:34 PM
Would guess it makes use of active power factor correction?

tulintron
12-01-2020, 08:55 PM
tulintron very interesting but as usual I expect that from you.
You mean you only swapped cylinders and that cures humming?
Take care buddy.Yes, Tsb. As you know, we always do internal tests in our laboratory. In view of the tests, we noticed that if a drum of line 4 is mounted in a unit of line 8, the power supply has a humming noise. When I return the correct drum, the buzzing disappears.

Engr, I'll try to be brief, but the lines I referred to the models:


Line 4 - C224, C284, C364
Line e - C224e, C284e, C364e
Line 8 - C258, C308, C368

Detail:
In my case, the noise only appears when the printer goes into a print job. But the noise is exactly at the power supply

allan
12-01-2020, 09:41 PM
By drum do you mean fuser roller?

tulintron
12-01-2020, 10:02 PM
By drum do you mean fuser roller?No, Allan. Here we change the drums of the Drum Units.

I know the problem with Engr. is in the fusion.
I just wanted to notify you that in my case, I managed to cause a hum in the power supply using a C364 drum in a C308 drum unit

M1963
09-10-2022, 11:57 AM
greeting,
i need a power supply shematic diagram for c308
does anyone know where it can be obtained.
thank you

DelawareJim
09-10-2022, 04:44 PM
Jim in Dover Delaware chiming in. I am in no way an engineer, just a Konica Minolta copier tech for 30 years. If you listen closely, you can hear that annoying "buzz" sound on just about every copier that we service. If it annoys the customer, we make the copier go into energy save/ sleep mode after a few minutes. Another fix is to cut to size a soundproof tile, remove the outer metal covering from the power supply and insert the cut tile and reinstall the metal cover. This absorbs most of the buzz noise. We have had excellent results with that. I would say 75-80% reduction in noise. Also, several times we have had the customer pay an electrician to install a dedicated 20A outlet for the copier. That really helps. It could be the copier is "starved" for current. A dedicated 20A outlet really does the trick. We have also noticed, if you have digital line filter installed, remove it and plug the copier directly into the outlet, the noise will become much less.
To check out the tiles we use, go to Amazon and paste this into the search bar "Sound Proof Sound Panels - 8 Pack 12" X 12" X 0.4" Acoustic Foam With Adhesive Stickers, Sound Absorbing Panels for Music Recording Studio Equipment, Home Sound Insulation A2S". They cost 29 bucks for a case and work great. One case of 8 tiles will take care of about 25 to 30 machines. We don't use any adhesive or tape for the install. They stay in place just fine.

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