A Better Quest Blower Control Mod

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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#1: Post by Nunas »

In another thread, I expressed some views and posed some questions about the two types of blower control on the Quest roasters, seeking a discussion of the fan control's best use. In summary, some Quest blowers vary from SLOW to high, and some vary from OFF to high. The latter has a huge deadband for off. From 0 to almost 4, there's no fan. Then from 4 to 8, the blower ramps up. On my M6, it's hard to tell by listening if the blower starts running; I find that really bugs me :lol: . On my M3 Mk-2, the fan was always on, but it was moving a fair bit of air even on low (0 on the control). There has to be a better way, and I think I've come up with it.

On my M6, I wired a trimpot (variable resistor) across the existing control. I used a 220k pot (which I had) but a 470k would give more flexibility. To install it, find the bare wire that comes from the existing control's wiper (middle contact). Solder the wiper of the trimpot to that wire. You'll notice that the wiper of the existing blower control is directly connected to one of the two other terminals; you want the other one :wink: Solder one end of a short piece of wire to that terminal and solder the other end of the wire to either end of the trimpot. The third terminal on the trimpot isn't used. If your Quest already has a resistor across the control (IE, your fan always runs), it's even easier. Just clip the resistor out, leaving its wires in place and solder the trimpot in place of the resistor. Here's a photo.

Plug the Quest into the mains and set the blower control to zero. Adjust the trimpot until the fan barely turns. Now turn the blower control up and down. Your fan should go from almost stopped to high speed over the entire range of the blower control. If you'd like to have an off position, turn the trimpot down a smidgeon until the fan stops. Now 0 will be OFF, and a slight turn will start the fan. The 220k trimpot still gives me an extremely slow fan with the trimpot turned down on my roaster, which is why I suggest using a 470K.


#2: Post by TonyC »

Hi Nunas,

I was looking at this photo and noticed that the adjustable resistor in this shot indicated '503' on it. Doesn't that value correspond to 50k ohms, not 220k ohms you mentioned in this mod? I might be missing something else, but thought I would ask, so as not to be totally confused...


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#3: Post by ira »

Every time I see pictures of Quest wiring it just makes me wonder. All that hot stuff just sitting out in the open.


Nunas (original poster)
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#4: Post by Nunas (original poster) »

ira wrote:Every time I see pictures of Quest wiring it just makes me wonder. All that hot stuff just sitting out in the open. Ira
Too true! These days, one would expect a little circuit board holding all the electronic parts and wires going here and there to the panel-mounted components. We used to call this point-to-point wiring 'kluge wiring' or 'breadboarding', and I have not seen it done like this for a very long time. But, on the other hand, since it is all behind the stainless panel, it just looks bad; it isn't a danger to the operator.


#5: Post by Beanz »

These days I would have expected that a small PCB made in Taiwan would be chepaer than the labour to hard wire the current birds nest configuration. I would suggest that running the roaster through an RCD would be a very good saftey precaution in order to guarantee operator safety.


#6: Post by CoolBeanz » replying to Beanz »

PCB's aren't that great, they are good for tracing following but when you run into issues it's always the PCB traces that burn because it can't take the amperage.

It's a bit like the old school stereos where they used to wire wrap onto posts. I used to repair those stereos and hands down they are superb. Unless we are talking about digital circuitry not having PCB is actually not a bad thing for performance... troubleshooting on the other hand is where it gets hairy :? :?