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trace and pad damage to Zenkit 1 circuit board (Read 2590 times)
goso64
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trace and pad damage to Zenkit 1 circuit board
01/07/23 at 01:33:28
 
As you can see in the pic below, 2 bad things happened when I tried to remove the volume control leads.

1. One of the traces became separated from the board (see pic). The red arrow points to the end of the trace (some metal still there.

2. The pads came off all 6 holes (see pic).

Before I expend the energy to try to patch this back together, is this worth trying to save or is a new board in order?

If so, any suggestions regarding getting the trace re-attached to the board? †

Also, is it possible to prepare the pads?

I'm disappointed - maybe this board is now junk.

Thank you all for your feedback.

[img][/img]

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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #1 - 01/07/23 at 04:32:09
 
 It might depend on how far along you are with the build. Less than 1/4 of the way, I might get a new board. The good news is that the trace is simply a wire stuck to a board, meaning that you can abandone it on both ends and run a wire from where it was supposed to go. Make sure that both ends are cut.
Just as importantly, it is possible that you are using too much heat with the soldering. How many watts does your solder iron have? Is it adjustable? What tip are you using? These are important questions trust me. I did some horrible work before I bought a good soldering station. Since you are removing pads and traces are coming loose that is important to consider.
 I won't say that the board is defective, but it is possible. When you were getting the pot out, what did you use? A solder sucker? Solder wick? Sorry for all the questions. Yup been there done that. It all matters.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #2 - 01/07/23 at 17:19:03
 
@4krow - many thanks for all these questions, as they lead me to research my soldering techniques.  Now I am a little more informed.  Here are the answers to your questions.

Any comments regarding restoration of the 6 pads that are gone?

1. I may be using too much heat.  My iron was set to 775 deg.  I did some research and seems I should be using 600-650 deg for tin/lead solder.  
2. Iím using a 60 watt Weller soldering station.
3. I was using conical tip - after some research, I should probably be using a bevel tip for this board.
4. When pulling out the pot, I applied heat only.  My solder sucker broke last week and I didnít think to use solder wick.
5. The trace in question makes several turns and goes all the way across the board, to the 1k resistor which is connected to the input tube so it's a difficult repair to say the least.
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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #3 - 01/14/23 at 01:21:10
 
Sorry for the late reply. The information that you have supplied tells me a few things:

1) 775 F of heat is way too hot unless you can get in get out fast. I run my iron at 650 and that is considered pretty hot too. The melting point of a lot of solders is between 380-450 degrees, so try experimenting with a much lower temp to see what happens.

2) The right tip will ensure the best heat transfer. I typically use a 2-3 mm chisel tip so the heat transfers more evenly. It works for most applications.

3) Solder wick is your friend when extracting solder from multiple connections. The solder must be removed from each connection as in the case of a volume control. Then bit by bit it may wiggle out as you apply more heat to the pins.
Fwiw, there is a product that is called Chip quik. It is actually an alloy made mostly of Cadmium. The melting point is low at about 200 F. So then you apply it to the original solder on the pads and it mixes with it. Now you can melt the 'new ' bunch of solder at a much lower temp, and it will stay molten much longer, giving you extra working time and ease with the solder wick to pick it up.

3) It's not likely that the traces can be repaired easily, but don't worry. A jumper wire can run straight across the circuit board where it ends up at the far connection. Make the wire long enough so it doesn't get in the way of anything or pick noise from nearby circuits.

You will be fine.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #4 - 01/14/23 at 01:34:30
 
Thanks for your reply. †I'll take your comments on the soldering to heart.

Agree - tried to repair the traces but it's not feasible. †I can try the jumpers but I already decided to get a new board last night. †I found that both traces from volume to the RCA inputs were lifted. I was concerned running 2 wires all the way across the board, over the components and to the inputs would result in noise so I bailed for the easier solution. †I'll let you know how it goes.

When I get the new board, I will mount the POT to the board and move the standoffs close to the edge of the enclosure so I don't have to run wires from the board to the POT. †

A secondary reason for me to restart is I need to redo the enclosure - it has so many holes it looks like Swiss cheese It's the first time I build an amp with an enclosure and I'm still learning so I chalk up the cost as training cost. †I've learned a lot and am enjoying it.

Cheers
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #5 - 01/14/23 at 03:38:11
 
UPDATE: †I tried running a jumper from the POT to each RCA input and also to each 1K resistor to the input pins of the tube. †I lifted the pads on every interface that I jumpered and pulled the trace of a bit and snipped it. (see pic)

Couldn't get it to work. †One channel was non-responsive and the other was always on, regardless of the position of the pot. †

It was worth a try - had nothing to lose. †

thank you again for your advice and encouragement. †Will redo once the new boards come in.

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Mannytheseacow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #6 - 01/14/23 at 03:53:45
 
Bummer! If itís not too late maybe just build a point to point amp and forget the board?  Youíve got all the components.
Though, you probably need a new volume pot if you got it that hot.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #7 - 01/14/23 at 04:11:28
 
Interestingly, I was thinking the same thing about point-to-point!  That will be my next amp.  Thanks again.  Cheers
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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #8 - 01/14/23 at 04:45:38
 
Play it as is and see what you think. It's fine that you have a new board coming. Also, if you decide to go the point to point way, you are going to have to buy what are called turret strips to connect the wires to. Mostly it will work, but you may have to lengthen leads and other stuff to get everything to reach. Just something to consider.
Let us know the outcome no matter which way it goes. I think that you have done the right thing for now. Who hasn't burned a trace or broken something or lost something? You wouldn't want to see my short comings in the shop, BUT I will gladly show off my successes!
And yes, I know what it is like to have a few too many holes in a chassis as well.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #9 - 03/23/23 at 01:16:50
 
After almost 3 months, I rebuilt the amp in a new chassis etc. Only reused items were the transformers. †I bought a new pot with solder lugs instead of board mount. †Anyways, I still have the annoying hum that increased with volume. †It sounds good but I'd like to figure out what's creating the hum. †

Any comments regarding where to debug the hum are greatly appreciated - Thanks!!

Some pics attached. Also, the DC Voltages at test points A and B are 10% below what they should be - dunno why

A = 315 vdc measured, s/b 346 +/- 10VDC
B = 273 vdc measured, s/b 309 +/- 10 VDC
C = 11.4 vdc measured, s/b 10.25 +/- 2 VDC
D pin 3 6922 = 2.8 vdc measured, s/b 2.6 +/- 1/2 VDC
D pin 8 6922 = 2.9 vdc measured, s/b/ 2.6 +/- 1/2 VDC






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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #10 - 04/24/23 at 18:58:22
 
 I am going to jump in here to make an observation. It was common for me in the past, to have trouble soldering in a way that was decent. I couldn't figure out why. It was only after I got the 'right' soldering station (in this case an888 model, made by Hakko), that I was able to make something that was both visually acceptable and much less electrically suspicious. Then, the solder mattered greatly as well. I ended up using 'Wonder Solder', what a stupid name, and continue to use it to this day. Yes, I have tried several solders and only wish that they worked for me but the results are not good. Dull looking joints, lousy flow, and more kept me using my favorite. The correct heat is very important, as you have found out with the damaged traces.
Looking closely at some of the tube socket connections, I see that the solder hasn't flowed evenly. No this is probably not an electrical fault, but may become one if a tube is taken out of the socket and the solder almost invisibly cracks.
This sort of this is seen at various points in the build as you have tried to get a lot of heat to say a speaker binding post, it isn't easy. Some of the blame there can be put to the position of the wire between two nuts rather than wound tightly around the end of the post, where wire soldering normally takes place. Again, there just may not be the intended physical strength in that connection.
My rule of thumb for pretty much every connection is to have a good mechanical connection before the solder is applied, rather than counting on the solder to be the glue. Many times I see wire just layed across an intended joint with a swath of solder to do the rest. In those cases, you then are relying on the solder metal makeup itself (mostly lead) to make the electrical connection and not the copper conductor itself.
When I find a wire to be small sixed for a solder hole in the circuit board, I will bend the copper wire into a J shape and then 'fit' it into the hole holding itself by the edge contact with the trace itself.

These observations are mostly self learned lessons as I went along for years trying get things at least better. Of course this is not intended so much as a criticism as a guide to follow. The intent is to have less troubleshooting of your own work, let alone defective parts or not so instructions for the build, etc.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #11 - 04/28/23 at 04:04:43
 
Thanks 4krow, Mannytheseacow, Sean, and bobc for the great suggestions. †Here's what I've done:

1. I replaced stranded wires on rca inputs and speaker outs with solid wire. †I curled the solid copper around the speaker outputs, no solder (see pic). †

2. I elongated the hole for the pot on my chassis since the higher quality Alps pot wouldn't fit. †

3. I replaced the pot using 22 gauge solid core wire - MUCH easier to work with!!

4. I twisted each pair of wires from the pot to the board (see pic). †

5. I also shored up the solder connections where it hadn't flowed evenly. †


What little hum that's left may well be inherent in the system. †The bottom line is that the hum is low that I only hear it during the dead space between track transitions. †I can live with it. †The amp sounds very sweet!

Thanks again to everyone for your help. †I've learned an awful lot on this project, my first amp. †




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Mannytheseacow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #12 - 04/28/23 at 04:32:43
 
Glad to hear it has quieted down for you. I think the residual hum is probably either in the transformer or needing more capacitance than specified in the schematic. Iím still fighting the same thing and many others posting here have the same experience.
If you feel the need to keep noodling now that itís done, there are several parts of the circuit you can direct-wire and skip the board. For example, wire the output transformers directly to the speaker jacks and Haden mod caps right to the tube sockets.
Cheers!
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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #13 - 04/28/23 at 14:06:13
 
 It's true. You can blame hum on just about anything and have a fair chance of being right. That is why there are lengthy discussions about it in one form or another. And frankly in tube equipment, your chances are even worse. That is just a fact.
 I am glad that you made progress with it. At least you can sit back for a while now.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #14 - 05/06/23 at 00:19:00
 
Thanks 4krow and Mannytheseacow for your input. †I have traced the noise to be a 120Hz signal that is 1/2 rectified (pls see pic). †

The scope pic was taken at the output of the anode of the 6N1P. †It appears on both pins 1 and 6 (red square on schematic pic), and it goes away when I turn down the volume. †

It does not appear at the gate or cathode or anywhere before the anode up to the input rca jacks. †It also does NOT appear on the other side of the 47K 1/2W resistors just above the Anodes.

It would seem the source is the input tube - or maybe someone has some further insights on this. †At this point, I'm just after root cause of the hum because I'm a stickler for this kind of stuff. †I'm happy with the sound of the amp. †



upload pics
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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #15 - 05/06/23 at 00:54:40
 
Thank you for a very informative post. I loved it when I got trouble tickets that read, 'broken', 'doesn't work' and the like. Of course, the input tube is the easiest thing to try. I would even add (with tongue in cheek) that the pins should be inspected and maybe cleaned. I just did this today to find pins that were never cleaned on some tubes that came in. FWIW, they were Mullards.
Aside from that, I would be curious as to what might be happening with maybe one of the SF4007 diodes. Total shot in the dark here, and really I am not a 'real tech', but I get my hands into stuff like quite often. You are right to try and find the origin here. I would.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #16 - 05/21/23 at 20:13:55
 
Thanks 4krow as always for your comments.

I have noticed something - the longer the amp stays on, the hotter it gets. †While that's to be expected, one problem I see is that the power x-former also gets hot and distortion seems to creep in and the hum gets worse.

The enclosure gets very warm to the touch in the area in front of the output tubes - but interestingly, the output transformers do not get hot!

My temp workaround is to place a metal plate in between the power transformer and the tubes (see pic). †It only solves the problem about 80%

Frankly, I'd like to know how to dissipate the heat from the box into the ambient. †I thought about drilling some holes around the output tube that is closest to the Power Transformer but I'm open to ideas. †The workaround is ugly. †

Oh, I'm attaching a scope pic of the diode after rectification. †I believe you asked about this...




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4krow
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #17 - 05/21/23 at 23:20:21
 
Ok, So I am NOT surprised at this. That is what tubes do best. Power transformers? Well, that would depend on the load that they are given. My Stingray amp is great, but at nearly 300 watts of heat for 50 watts of audio output, I might not listen as long in the summer.
To help with this, I use, as many as I can (there are 12 tubes to cool), Pearl tube coolers. They are not expensive, and they work.
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goso64
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Re: trace and pad damage to Zenkit 1 circuit board
Reply #18 - 05/24/23 at 12:40:32
 
4krow, thanks for the tip.

I was only able to find one seller on ebay who is selling MPCF-9 Pearl tube cooler for my Svetlana SV 83 output tubes (EL 84 compatible). With shipping and taxes about $70 so I'm wondering if you can suggest an alternate source.

I was also thinking about trying a small battery operated fan. I found a usb-chargeable one for about $13 on eBay and I may try this forest, without the tube coolers.

Thank you for your support
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