Park Tools DS-1 digital scale has died

[TheNormsk]

So I have a not very old (about 1-2 years old) DS-1 scale and while hanging a bike on it the other day it fell off its hook and dropped six feet onto the concrete garage floor. At the time I was "oh crap!" But I was relived to see no apparent damage to it and it continued to work.

Now several days later it is dead. I guess some electronics or something died internally.

Now I've contacted Park Tools to see what I might be able to do about this but assuming it's out of warranty and if i get no help from Park I'm wondering if there is any hope in taking it apart to repair it?

Buying a new scale is not really an option as I just got made unemployed this week so I really should be counting the pennies. Time I now have to try DIY repairs.

Im kind of disappointed with its fragility. Has anyone repaired one of these before?

[flipnidaho]

Have you checked the battery?

[TheNormsk]

Yep, the first thing I did was change the batteries.

[DennisF]

If you can't fix yours, here is an affordable alternative:

Amazon.com: Digital Hanging/Fishing/Luggage Scale: Sports & Outdoors

They are even cheaper on eBay. It has every conceivable feature and accuracy compares well to our postal scale on light stuff. It also compared closely to an airport scale when we used it to weigh a suitcase.

Heck, I'd take it apart and try to fix it -- what have you got to lose? I can't tell from the picture if it is easy to dissasemble or if the two halves of the case are glued together. I have disassembled several such devices with minimal damage by using an X-Acto razor saw to cut little slots in the corners of the device, then prying with a small screwdriver.

My last such project was Wife's uh, lets say personal device, accidentally went thru the washer with the laundry. Operation successful!

If everything looks OK, but it has a printed circuit board and you have a soldering iron, reheat all the solder joints. Solder tends to crystalize and can form invisible cracks that are fixed when the solder is melted.

Edited to add that obviously you can't hook your bike on the tiny hook. I use a loop of nylon rope to attach the bike. If the rope is on the scale when you turn it on, the auto-zero tare feature ignores the weight of the rope.

[TheNormsk]

That other scale looks like a bargain. I'll consider that. Thanks.

I took the DS-1 apart. It has very fragile wires inside. While investigating it two of the wires, one to the sensor and one to the battery broke. I was able to solder those back.

I started testing current flow with a multimeter and immediately found when I short circuited across the components (triodes?) marked Q1 or Q2 that the unit beeps and then turns on. It is then fully functional. I can switch it off and back on (if I do it immediately). If I wait a few seconds it no longer works and won't switch on again. I would guess that once the capacitors discharge the on/off button no longer works.

I can't see or find any thing else wrong with it and it seems to be fully functional once it is on. Re-soldering the contacts may work but my soldering skills are not that great so I'm reluctant to try this.

What I think I shall do is wait a couple of days to see if Park gets back to me. If not, I will hack the unit and solder a couple of wires to Q1 so i can manually short circuit it when I want it to switch on.

It's a hack but it should work as I don't use this that often.

[DennisF]

Interesting. Good detective work.

A caution before you solder in the short-circuit wires. You are saying that you short across something with your multimeter, and it turns on. I doubt that is really the case -- I doubt that you are really short-circuiting anything. A short is connection that offers almost no resistance to the flow of electricity. You would make a short with a jumper clip or your multimeter in the Amperage mode.

What mode is your multimeter in? If in Voltage, it is acting like a very high resistance -- something that flows very little electricity.

If in the Ohms setting, then it is providing a very small amount of electricity. Most likely it will only turn it on when the leads are placed in one direction. If you reverse the black and red leads, it probably will not turn on.

So let's figure out what exactly the multimeter is doing. If it is in Ohms setting, then my guess is that a resistor that is supposed to feed a small amount of electricity to something to keep it active is damaged. The capacitor is OK. It getting charged when you hold the ohmmeter to it. And it is storing electricity, because it will turn on if you are quick about it. Without constant voltage applied to it, a capacitor will drain quickly.

I don't guess Park has a schematic on their web site?

BTW, Q1 & Q2 are transistors -- yes technically a triode, although that term normally refers to a type of vacuum tube.

And yeah, you don't want to resolder those surface-mount components unless one is known to be bad. I understand that they can be replaced by hand, but have never done it and know nothing about it.

[TheNormsk]

Well Park got back to me but won't do anything because it was dropped and they do not offer a repair service. Suggested I go out and buy a replacement. Great!

On the short circuiting Q1 I was also dubious if current from the multimeter was energizing the circuit to activate it so I tried this also with a jumper wire. The short circuiting of the transistor (thanks for that as its been 25 years since I did detailed electronics in school) still switches the unit on.

For now I'm going to drill a hole in the back on the casing. I will solder two leads to the two prongs of Q1 that causes the unit to switch on and run the leads out of the unit through the drilled hole. The two leads will have bare ends for now.

When I want to switch the unit on I will temporarily touch the bare ends which will start the unit. I will not permanently jumper the transistor as I am not sure what that will do to the unit long term.

Over time if this proves successful and the scale remains accurate I will see about attaching a push button switch on the back to start the unit.

Let the hack begin!

[TheNormsk]

Oh on a side note I found out that I bought the unit in January 2012 so it is 14 months old. Figures, just out of warranty!

I also noted when I took this apart that the circuit is dated from 2007. I looks like park has a lot of old DS-1s floating around if I procured such old stock.

[DennisF]

OK, cool on the short circuit. It still makes me uncomfortable. Try putting a resistor across it instead of a dead short, and if it works go for that.

It may not turn on when you connect those two transistor legs like a dead short does, but may cause the on-off switch to work.Try different resistors or use a potentiometer to test. If that is the case, you have fixed it. Solder the resistor in place and enjoy!

[deano machineo]

A positive word about Park tools customer service. I had a DS-1 that the display started to go out after a few months. I emailed Park, received a phone call 24 hours later. They sent me a new one and didn't even want the old one back. Maybe it was a common problem they knew about or not. It had to have been the easiest warranty replacement experience I have ever had. Took the old one apart one day and found the display was kinda bent during assembly causing the LCD to fail. Put it back together and it works to this day.

[cman8]

Bought this on fleabay. Works great and I love the backlight design

[TheNormsk]

Cman, is that accurate to 1g or 10gs like all the others?

[TheNormsk]

As an update to this Park did come back to me and offer to try to repair it after I pointed them towards this thread but I didn't see the email for a week and I already performed the hack and have this working again to the extent that I don't even need to jumper Q1 anymore.

I drilled two small holes in the back of the case for my "jumper" wire, and I followed the circuit and discovered that I did not need to solder the jumper to both sides of the Q1 transistor but that I could solder one lead to the + terminal of the battery pack (much easier job). The other lead I soldered to the side of Q1 that only has one lead. I also used a bit of tape to help hold the lead as the solder joint is fairly weak. Initially I tried to just heat the existing joint and push the lead in but there was not enough solder for that. So I fluxed the joint and added solder with the lead. The two leads then passed through the holes to the back where I can short circuit Q1 when I want to start up the scale.

However since I did this I have found that I no longer need to short circuit Q1. I'm not sure if the flux I left on the board is causing a current leak that is working magic or if the reheating and new application of solder fixed a solder break in Q1 though I am thinking the former as I forgot to clean this off and when i applied it it started the unit up. But whatever the cause I'm reluctant to take it apart again and clean the flux as the unit appears to be fully functional again.

Below are photos of my hack.





Anyway right now the on-off button is now working without needing to jumper Q1 and the scale appears to be accurate.

[DennisF]

Good job!

[SS Hack]

Are the super cheap scales accurate?