HeaterMeter v4.2.4 Trouble - Blower shorted


 
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Chris S (AsstroChris)

New member
So I have completed a build of the Version 4.2.4 hardware, loaded up the Pi software and everything is running fine when connected to the 5V power through the PI, however when using the 12V power, I am having exactly the same issue as described in this thread: http://tvwbb.com/showthread.php?48416-HeaterMeter-v4-1-Trouble-Fan-Not-Working/ when i plug in the pit probe. I am reading continuity between ground and blower pins on the RJ45 jack. I'm having trouble finding a possible short, the large MOSFET is NOT shorted, although it looks like it is from the glare in the following pics. Any help would be greatly appreciated.

https://www.dropbox.com/s/770tjv0vzvhxuxf/2016-07-26 15.34.43.jpg?dl=0
https://www.dropbox.com/s/ythc99bg955mdo9/2016-07-26 15.34.29.jpg?dl=0
 
I would reflow all your solder points without adding more solder to the iron tip, this may remove a short if there. Then clean the board with a small brush and rubbing alcohol.
 
Keep in mind that the entire top of the board is covered by a ground plane, if any solder bulges over its joint it could touch that ground plane and short out.... Also look inside your CAT5 jack at the legs in there to make sure none of them are crossed over and shorting and there is no metallic debris in there....
 
So I finally got around to debugging this board. I do a lot of electronics work so decided to get a decent desoldering iron with a little pump on it, works awesome... I narrowed down the short to have to be somewhere between the RJ45 jack, C12 or L1. I removed all three and when I removed L1 the short was gone. I am reading continuity between the two legs of the inductor and about .8 ohms resistance, so I must assume this component is bad. With the RJ45 jack and 45uf cap back in place, and only L1 off the board, I have no short between the blower and ground pin. I guess I need to get a replacement?
 
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An inductor IS a short, as it is just a coil of wire... There will be some small resistance from the wire itself but it will be low, the REACTANCE, which is referred to as inductance and measured in Henry's is the most important property of an inductor....

The power to the blower passes right through that inductor, so without it your blower will be DOA. See below a diagram of the blower circuit I made up to help someone a while ago...
HMv4.2_BlowerDriver.jpg


It seems like what you have is a brown-out scenario, where the PS is drooping down low enough to reset the HM, WHY is the question. Could be just a bum PS, could be a short somewhere on your board, could be a bad blower I guess (short to gnd in the blower).

When powered by 12V with the blower disconnected does the HM still brown out?

You should try spinning up the blower connected to the PS directly, put the red wire in the hole and touch the black wire to the outside of the PS plug (while it is NOT connected to the HM, be careful not to short the inside wire to the outside). This will confirm the blower is good and the PS can spin it, or not....

If the BLOW pin is shorted to gnd then the most obvious components to check to see if they are shorted/bad would be D2, and you'd want to check the value and polarity on C12 and C7 as well, and also confirm the value of R4? (the 22k resistor).

That said, if it is a solder bridge then it's hard to tell what to check looking at the schematic diagram, you would have to look at the traces where they come near other traces and solder joints.
 
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Ok, D2, the 5819 is blown. I think I had a power problem with an old 12v adapter, I already replaced Q3. My inductor still could be shorted, but I can start by replacing D2. In effects pedals I often see 5819 used for safety on the 9v supply and I can easily swap it for a 4001 or 4007, but I assume here we are looking for a specific voltage drop. Do you have any idea of a replacement I can use? I have 4001, 4003, 4007, 914, 34a off the top of my head.
 
OK, glad you found the culprit... The 1N5819 is Schottky rectifier, not a general purpose diode, I assume there is a reason why Bryan used it rather than just a general purpose there. I would use the right part there or a cross referenced replacement or a similarly rated schottky diode....

On the inductor, I once repaired a HM that had a reverse polarity power supply connected to it.... Got it back working easy enough, but the blower would go from off to super fast right away, it ramped up a bit at the end but wouldn't run slowly. Turned out the inductor got fried, but I can't recall how it tested when bad.... I think it got "more" shorted, meaning instead of the normal low resistance it had no resistance (or inductance) because the windings melted and shorting out inside. So, moral of the story, the blower will work even with a shorted inductor, it just wont work RIGHT. If the inductor were burned open then the blower would not work.
Another note, even with a damaged inductor (shorted, not open) the blower should function properly when it is set for PULSE mode in the HM config.
 
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Yea I was just reading up on the schottky diode, there is probably a reason he used it and a 4007 could cause problems. My neighbor makes hifi equipment, I'll see if he has one then move on to figuring out if the inductor is shorted. We'll see if f the fan runs "wrong" or semi correct in pulse once I replace D2. This explained why I saw ground on one side of the inductor, which is good because I still felt I hadn't found the real cuplrate here. Also, I figured you should see continuity through an inductor. Always learning
 
To be clear, in my experience the blower will work when the inductor is shorted, but in Voltage Mode it will not work properly. It will go from 0 to about 75% when the blower comes on and only ramp up a slight bit in the upper percentages (it will not run at a slow pace ever). This is in Voltage mode where the feedback circuit is required. In Pulse Mode the blower seemed to work perfectly with the shorted inductor, it ramped from a trickle to full blast just fine. In fact switching from Voltage to Pulse mode is what keyed me into the fact that the feedback circuit was damaged, running 5% in Pulse mode I got a trickle or air, running 5% in Voltage mode and it was blowin' up a storm...
 
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