Quoted from oldschoolbob:...A lifted pad on this board would be game over. I doubt it could ever be repaired...
Not really Bob. It's just a connection, it can be repaired with some greenwire. I design high power transmitters for a living, and I've vaporized huge traces when things go wrong. Rather speculator when it happens, resembles an arc welder going berserk - but we just repair the traces and go on.
Quoted from oldschoolbob:I've never been a very patient person. Went to the shop tonight to try the new glasses. They'll work great for inspection work but not so good for working under. The focal length is just too short.
While I was there I decided to try the two solder irons to remove the old chip. Both irons set on 500*F. Just didn't seem to get hot enough. I tried several times but I couldn't get it loose.
Plan B was the ChipQuik. I buttered it up with their paste and added the solder. It came right off. I picked up the solder blobs with the iron tip and cleaned it with solder wick. Then I washed it with alcohol. It looked pretty clean and I don't see any damage.
After looking at the photos I see a couple of specks of solder on pins 8 and 16. Tomorrow I'll hit those again with the solder wick.
One small step for man - one giant leap for Bob.
Thanks
Bob[quoted image]
Looks great!
Quoted from oldschoolbob:One small step for man - one giant leap for Bob.
Beautiful! Easier than pulling pin headers off Bally MPU boards? 
Quoted from oldschoolbob:I received the magnifier glasses today. My first impression so far - You can't use both lenses at the same time.
I bought a pair like this:
ebay.com link: itm
You can install one or two lenses (they're large) to get more zoom options, but they get a little heavy so you have to tighten everything to stop them drooping:
This ones very similar to yours but also includes lower zoom lenses - they're harder to find in online stores though:
ebay.com link: itm
I spent most of the day working on the practice board. Dang those parts are small. First attempt was a couple of diodes. There're round and very hard to hold in place. I have some flux paste that (I think) has solder in it. That seemed to work a little better on the small parts. I also tried different soldering tips.
S20191110_0008 (resized).jpg
S20191110_0009 (resized).jpg
Then I tried some capacitors and resistors. Not much better. I need a lot of practice.
S20191110_0002 (resized).jpg
S20191110_0010 (resized).jpg
Next I tried one of the IC's. I followed Dave's video and it came out pretty good.
So far I've found the round chisel point tip works pretty good for me - especially on the IC. The flux paste (with solder) works good on the small parts but I don't think it would work on the IC's. Liquid flux worked fine. I've always soldered by heating the part and the pad and adding solder. That don't work so well with these parts. So I add the solder to the tip then touch the the joint. The 0.015 solder is small but the 0.031 works just as well with this method.
I'm going to practice more the next couple of days then maybe I'll be ready to tackle the real work.
Thanks
Bob
Use the same method with the small caps/resistors. Add flux. Add some solder to the iron tip, hold the component in place with tweezers then touch the joint with the iron tip.
The chip soldering looks great!
That's pretty much what I been doing. And I'm getting better at holding the parts in place with the tweezers but I was worrying that the component was not touching the pad - being held up off the surface with the tweezers. But after thinking about it, maybe that's not a problem as long as I have solder under it and it's secured. Where I was getting in trouble was when I soldered the part in place and then I'd go back and reflow to be sure the component was down. I definitely need more practice.
I was amazed at how easy the chip went. Maybe just beginners luck. I had a couple of bridges but just hit it with the iron and picked it up. Didn't even need solder wick.
Bob
Quoted from oldschoolbob:I was amazed at how easy the chip went.
I'm hoping you're giving others watching the confidence to try surface mount and not be intimidated.
I have always been intimidated by SMD's. I remember when those Chinese component testers came out and I wanted one. But they were all kits with a bunch of surface mounted components. I didn't get one till they came out with assembled testers.
If (at my age) I can do it anyone can do it. It just takes some practice.
Quoted from G-P-E:"Melfs"
Yeah, they're quickly getting less popular as they're not as easy to manipulate with pick and place equipment.
I've used the square'ish 'MELF' PIN diodes in my designs for decades - never knew the round ones were considered MELFs too!
Quoted from oldschoolbob:That's pretty much what I been doing. And I'm getting better at holding the parts in place with the tweezers but I was worrying that the component was not touching the pad...
Bob, I'd be a little careful using tweezers with the caps and resistors. The small parts can be a little fragile. If you accidently give the tweezers a little twist or nudge after one end of the part is soldered, you can break the end of the part. Try using a small wooden toothpick (trying to think what else you might have laying around) to gently holding the parts in place by applying a miniscule amount of pressure from the top. After you get good at it, you probably won't even need to hold them in place.
The caps have a bit too much solder on them...but no harm. You just want a nice fillet. You could always wick excess solder off for appearance sake, but at the risk of damaging the part by fooling around with it too much. By the time you got to the IC, looks like you were getting the hang of it!
pasted_image (resized).png
Thanks Mark, I've seen those caps crumble before.
Today I worked again on the practice board. I tried some IC's.
I was feeling comfortable so I went for the real thing. It went on good except I got a solder bridge. I worked on it for an hour trying different solder tips - different solder wicks - different fluxes. I just can't seem to clean the bridge so I quit for the night.
The problem might be all three legs ( 6 - 7 - 8 ) are ground and look to be connected to a ground plane. I have extra IC's (4051's). Would you replace the chip or just let it go?
Thanks
Bob
S20191111_0010 (resized).jpgS20191111_0011 (resized).jpgQuoted from oldschoolbob:The problem might be all three legs ( 6 - 7 - 8 ) are ground and look to be connected to a ground plane. I have extra IC's (4051's). Would you replace the chip or just let it go?
If you're having trouble, I'd let it go since they're electrically the same connection. Last thing you want to do is overcook the chip with the iron.
Quoted from Quench:Last thing you want to do is overcook the chip with the iron.
I hope I haven't already done that. I messed with it quite a while.
Are you ready to turn this thing on? Clean up the flux and verify there's no solder whisker shorts across any other pins first.
When two SMD legs are bridged wipe your iron tip clean/dry and then use it to wick off the bridged solder. The excess solder will want to move to the dry iron tip and surface tension will keep enough solder on the pcb and smt leg.
Since those three legs are all going to ground its not required to fix it.
I checked my work and assembled it enough to test. Same results. None of the pots (encoders) work. I did check the switches on the pots and they 'seem' to work. At least some of them do - it's hard to tell because most switches just center the cursor and I can't move the cursor to un-center it.
I may have overcooked the 4051 trying to remove the solder bridge. I have plenty of 4051's and 393's. Next I'll replace the U2 and U1 but it's looking like I have just got a parts scope.
Bob
Quoted from oldschoolbob:...I may have overcooked the 4051 trying to remove the solder bridge...
I doubt if you fried it.
Quoted from mbwalker:I doubt if you fried it.
I agree especially since it's still doing the same thing.
But what the heck - I got the chips and I don't have anything else to do - There's snow and ice on the ground and it's 12*F outside.
I just hate that we didn't fix it after all the work you guys put into this.
Quoted from oldschoolbob:I agree especially since it's still doing the same thing.
But what the heck - I got the chips and I don't have anything else to do - There's snow and ice on the ground and it's 12*F outside.
I just hate that we didn't fix it after all the work you guys put into this.
You and Quench were doing all the work, i justed started chiming in at the end.
Not so. You, Quench, Andrew and everyone have have contributed to this project. And not done yet. I just feel certain the problem is on this board and not the main board. Everything seems to work except those darn encoders.
Today I replaced U1 - no change.
I keep going back to what Mark said back in post 105.
Quoted from mbwalker:it would be the C line is stuck low.
Except X5 does seem to respond. The push switch for VO is working but the encoder is not working.
What would keep the other lines (X4 and X6) stuck low? (X7 is not used).
I just noticed that every one of those non working lines has a diode. None of the other lines have diodes. I know a bad diode in a pinball game can cause all kinds of problems. ???
Thanks - you guys have been a great help
Bob
Quoted from oldschoolbob:I just feel certain the problem is on this board and not the main board.
There is one way to find out... That is if you're prepared to swap boards with your new scope..
Quoted from oldschoolbob:What would keep the other lines (X4 and X6) stuck low? (X7 is not used).
We never quite got into that detail to see what those lines were doing when we were hooking up your scope to those lines.
Quoted from oldschoolbob:I just noticed that every one of those non working lines has a diode.
Test them all in circuit with your multi-meter.
Just out of curiosity, (scope off) if you measure the resistance on one of the encoders between the middle leg and either side leg, does the reading change between open circuit and closed circuit as you rotate the encoder?
Quoted from Quench:There is one way to find out... That is if you're prepared to swap boards with your new scope..
Believe me I've thought of that. But I just can't force myself to open that brand new scope.
Quoted from Quench:Test them all in circuit with your multi-meter.
That's first on my to-do list.
Quoted from Quench:does the reading change between open circuit and closed circuit as you rotate the encoder?
Not sure what you mean?
Thanks
Bob
I was looking over the photos of this board and found a bunch of resistors and transistors (?) that are not shown on the schematic. I count 8 transistors and there are 8 encoders. But they're around the LED's. But there's only 7 pair of LEDs that I can find.
What are they?
Where did they come from?
What do they do?
Maybe this isn't the correct schematic?
Could that be the cause of this problem?
Bob
IMG_3969a (resized).jpgIMG_3978 (resized).JPGIn the first group on the upper right there are 3 circles with 4 transistors but there's only 3 LEDs behind them.
Bob
Quoted from oldschoolbob:I was looking over the photos of this board and found a bunch of resistors and transistors (?) that are not shown on the schematic. I count 8 transistors and there are 8 encoders. But they're around the LED's. But there's only 7 pair of LEDs that I can find.
What are they?
Where did they come from?
What do they do?
I count 7 transistors and they're all located on the back side of where the LEDs are.
[EDIT] Oops, there are 8 transistors.
Quoted from oldschoolbob:Not sure what you mean?
Set your multi-meter to low resistance mode.
Put a meter lead on the middle encoder pin "C", put the other meter lead on the "A" pin. You should measure either short or open circuit. Rotate the encoder slowly and you should see the state of those two pins alternate between short and open circuit.
Do the same between pins "C" and "B" - should get similar behavior.
I got it. Should the B and A be opposite? - B closed and A open?
I'll trace those transistors to see when they go. Wonder why they aren't on the schematic?
Wrong Schematic?
Bob
Quoted from oldschoolbob:Wrong Schematic?
Schematic might be a previous model, the transistors are probably MOSFETs switching the LEDs.
Quoted from oldschoolbob:Should the B and A be opposite? - B closed and A open?
No, see the animation showing how the outputs change as the encoder is turning here:
https://en.wikipedia.org/wiki/Incremental_encoder
Imagine a "1" is when the pin is shorted/connected to the "C" pin, and a "0" is when the pin is disconnected from the "C" pin.
Todays findings:
Most of the diodes read .55 in one direction and .89 in the other direction. One diode read .55 and .72. On two decoders the diodes read .55 and OL (all 4 diodes). All diodes are marked "T4".
The transistors are marked 3EM followed by ":6 " - the :6 is rotated 90*. I haven't traced what they are connected to but they are all just above the LEDs.
The decoders were very strange. When first connected the meter reads OL - when I turn the pot it jumps to 20-30 M ohms then quickly goes back to OL. I tried 3 encoders and got the same results. Same results connected to center/right and center/left. At no time did I get a steady short.
Bob
Quoted from oldschoolbob:Todays findings:
Most of the diodes read .55 in one direction and .89 in the other direction. One diode read .55 and .72. On two decoders the diodes read .55 and OL (all 4 diodes).
Regarding the diodes, you're probably seeing a sneak path thru the other circuitry, especially since it is more than one diode. I doubt if you would have multiple diode failures. If you want to really verify, remove the diodes.
Quoted from oldschoolbob:Believe me I've thought of that. But I just can't force myself to open that brand new scope...
I know you really want to do this ...But then common sense kicks in a says "Don't tear apart the new scope." LOL, I wouldn't either.
Quoted from oldschoolbob:On two decoders the diodes read .55 and OL (all 4 diodes). All diodes are marked "T4".
If you rotate these two encoders, does the OL reading go away?
Quoted from oldschoolbob:The decoders were very strange. When first connected the meter reads OL - when I turn the pot it jumps to 20-30 M ohms then quickly goes back to OL. I tried 3 encoders and got the same results. Same results connected to center/right and center/left. At no time did I get a steady short.
The encoders click as you turn them right? These are 12 position encoders according to that schematic you linked.
Data sheet says closed circuit resistance is maximum of 3 ohms. So you should be seeing closed circuits as you slowly rotate the encoder.
Datasheet for the encoder is here - there's no mention of how the switching occurs as you rotate other than it's not optical - presume it may be magnetic/reed?:
https://www.mouser.com/datasheet/2/54/bourns_pec12-1159230.pdf
Quoted from mbwalker:I doubt if you would have multiple diode failures.
I agree. I was hoping to find a diode with a dead short in both directions.
Quoted from Quench:If you rotate these two encoders, does the OL reading go away?
I tested those diodes several times with the same results. I didn't think about rotating the encoders until after I was done for the night. I'll try again tomorrow and this time I'll rotate the encoder.
Quoted from Quench:The encoders click as you turn them right?
There is very little click (if any). My solder station has an encoder with a very noticeable click - but not on these. Also the encoders on the new scope feel the same - no click.
I tried three encoders (several times) and never saw a closed circuit. The meter starts OL then jumps up then right back to OL. Not at all what I expected from the animation. I'm probing right on the decoders - after the diodes. Exactly where you pointed to in the photo. Even the same three decoders.
Bob
Quoted from oldschoolbob:I tried three encoders (several times) and never saw a closed circuit. The meter starts OL then jumps up then right back to OL. Not at all what I expected from the animation. I'm probing right on the decoders - after the diodes. Exactly where you pointed to in the photo. Even the same three decoders.
Hmm, well do you feel like hooking it back up and powering on. Then toggle a short with a screw driver a few times between pin A to pin C on one of the encoders while watching the display to see if there's any reaction? Choose an encoder that would normally make an obvious change.
BTW, have you ended up replacing all 3 SMT chips or is there still one not done yet?
I have not replaced all 3 chips - only U1 and U2.
Quoted from Quench:Then toggle a short with a screw driver a few times between pin A to pin C
That sounds dangerous. But I'm willing to give it a try.
I'll let you know tomorrow.
Thanks
Bob
No shop time today but I do have some news. A while back I contacted Hantek about getting this oscilloscope repaired or obtaining parts. They finally responded. The guy told me I needed a new "keyboard" and he would send me one for $8.00 plus shipping. I asked for a description of "keyboard" - photo or drawing. If he's referring to the Front Panel Circuit board, that we been working on, I'm all for it. So far he hasn't gotten back to me. But it is the weekend in China. We'll see.
Bob
Wow that's cheap. Might be worth asking for the flat ribbon cable too.
Since you're invested in your current board, you may as well swap the last SMD.
Things must move at a much slower pace in China. I have been in contact with Hantek for almost a week and still have not resolved the situation. One thing he suggested was to remove the ribbon cable and switch it end for end. I tried that but still no luck. He said he would send me a new "keyboard and cable" but I had to pay shipping - $25.00. I asked about replacing the main board but he said if the "keyboard" don't fix it that I must send it in for repair - A new main board is $177.00. I agreed to pay the 25.00 shipping and he said to pay it with PayPal to some 'hotmail' account. Does that sound fishy? Besides, I don't have a PayPal account (and don't want one). I asked for an invoice with request for payment so I could pay with a credit card. That was 24 hours ago and haven't heard back.
I'll keep you posted.
Bob
Quoted from oldschoolbob:PayPal to some 'hotmail' account. Does that sound fishy?
When you pay via paypay, the receivers account is based on their email address registered with paypal. To be honest them using a hotmail account doesn't surprise me much.
They probably have cheaper shipping options so long as you don't mind waiting a little longer.
Quoted from oldschoolbob:he said to pay it with PayPal
Using a credit card to pay in China is probably more of a hassle with them than paying with Paypal as he suggested. (I've been to China 9 times and know some of their hassles). If you pay with Paypal you are covered (like using a credit card) if you don't receive the merchandise, or if you need to return a defective product, etc. If you don't want to open a Paypal account, and you can't get the purchase with your credit card, I'd be happy to pay for it with my Paypal account and you can reimburse me with a check in the mail.
P.S. I'm enjoying your thread.
Jethro, That's very kind of you to offer your help. But it made me think - a good friend of mine (and fellow pinballer) most likely has PayPal. I just sent him a message. If he has an account he will help (besides he owes me).
Thanks
Bob
Quoted from Quench:To be honest them using a hotmail account doesn't surprise me much.
It just seemed strange that they have their own website (hantek.com) and their own email ([email protected]) that they would use hotmail for their PayPal account.
I checked shipping from China and 25.00 is not unreasonable. Especially if I get the parts quickly and it fixes the problem
It makes me wonder how these places in China sell stuff on Ebay for a couple of dollars and have free shipping? However, most of that stuff takes 6 - 8 weeks delivery - slow boat from China?
Bob
Quoted from oldschoolbob:It makes me wonder how these places in China sell stuff on Ebay for a couple of dollars and have free shipping? However, most of that stuff takes 6 - 8 weeks delivery - slow boat from China?
Bob
Government subsidized shipping.
Quoted from G-P-E:Government subsidized shipping.
Yep. Amazing. I've bought items that cost less than a dollar and included free shipping from China! Geez, I can't even ship a padded first class envelope across town for that! Good old government subsidized shipping.
This may be the end of our oscilloscope fun. I’ve had my replacement scope for over 4 weeks and after a week of correspondence with Hantek about getting replacement parts, Amazon just requested that I must send back the old scope. I’m not saying that Hantek and Amazon have been colluding (it’s probably just a coincidence) but they never mentioned a return until today.
I asked Amazon what if I already threw it out. They said they’d charge me the full price for not returning the old unit.
The sad part is all the work we’ve put into this repair (and some expense) is all for nothing. Well, maybe not all for nothing - I have learned a lot the past few weeks.
Thank you all for your kindness and lessons.
Bob
Quoted from oldschoolbob:Amazon just requested that I must send back the old scope.
Boo!
It's been a valuable thread. Even I've learnt from it.
Quoted from JethroP:I was learning a lot too and enjoying this thread.
Bought yourself one of those practice surface mount kits yet?
Quoted from Quench:Bought yourself one of those practice surface mount kits yet?
Noooooo!! What I learned was that I don't ever want to replace surface mount components! Especially those IC's! 
Quoted from JethroP:Noooooo!! What I learned was that I don't ever want to replace surface mount components! Especially those IC's!
Nah, easily done more than thru hole. I think we managed to to convert Bob. Been doing it for almost 30 years, would never go back to thru hole.
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