Tutorial for recapping?

[painttoad]

I bought one of those small magnetized bowls Harbor Frt. sells in the automotive tools section. Most screws are magnetic and stick to the bottom of the bowl, the fasteners that don't, are at leased still in the bowl.

also doubles as a clipped lead collector

 

[Lavane]

also doubles as a clipped lead collector

Ya, the ones that don't fly off across the room somewhere.

 

[gadget73]

in addition to the excellent advice offered already, I'll suggest picking up a cheap set of calipers so you can measure caps where the dimensions matter.

 

[j!m]

Since I'm generally working on older gear (pre-1980), going up a step on voltage, beyond what was originally used, generally gets me the same form-factor from 40+ years ago. Meaning: the physical size matches the old ones.

And besides the physical size, be mindful of "lead spacing" which is how far apart the wires are coming out of the can. If this is off, your board will be a mess, with nothing fitting correctly.

Lifted traces are something you should be prepared for, because most of the older boards lift traces quite easily. Solid tinned wire I find to be the best way to replace broken/lifted/damaged traces. I make a loop on one end (sometimes both) and place it over the component lead at each end, and then re-flow the joint. You may need shrink tubing on the wire, if it is passing over other traces to do the repair. It's fiddly work but taking your time will get it done.

As far as capacitor selection, refer to the service manual. Unless you are experienced and understand the circuit design(s), you are not in a good position to "improve" the original choices. Generally something "low ESR" is specified in the service manual for example. Obviously, there are plenty of very smart people here that can help with specific replacements, but there is a lot of "experience" that needs to be gained before you go "improving" things.

 

[Leestereo]

Is there a formula for this? Or do you just lower a bit and give it a listen to determine if its to your liking?

Always like to learn .

Athanasios

The F3 of a high-pass filter can be calculated with the following formula: F=1/(2πRC), where "C" is the capacitance in Farads, "R" is the resistance in ohms and F is the frequency in hertz. For RC high-pass filters, a good rule of thumb is to use a capacitor that gives a F3 that is 2 octaves below the lowest frequency of interest (20Hz), hence, a F3 of 5Hz. Further, if the capacitor is an electrolytic type, to minimize LF distortion (see http://www.diyaudio.com/forums/parts/192811-capacitor-measurement.html#post2643470), it is good practice to use a capacitor that is ~10X the size required to achieve the F3=5Hz, e.g., if a 1µF film capacitor is sufficient to give F3=5Hz, an electrolytic capacitor substitute should be 10µF. However, since one cannot assume that the electrolytic capacitor installed in the filter followed this ~10x size recommendation, it is best to calculate the replacement film capacitor size.

 

[conductivity]

Hello all,

I'm always reading about how you should replace the capacitors on older gear. I'm relatively handy in most all areas with electronics repair being the notable exception, mostly due to never doing it. I can, however, follow directions and I'm sure there is likely a good tutorial on how to remove and replace old capacitors somewhere (likely on AK somewhere), but I can't think of good search terms that would find it for me, so I'm going to punt and ask the question here. So, does someone have a link to a tutorial on how to replace capacitors?

Thanks!

Beyond what has already been mentioned about capacitor specifications, it is about workmanship of the soldering. There are some important things to know. If a sticky thread is needed, I have explained important things here:
https://audiokarma.org/forums/index...placement-of-electrolytic-capacitors.1004088/

 

[theflattire]

WHat caps actually make a difference?
Ok, I got the coupling caps between the driver and power tube:
.22uF 420volts

How about the two coming off the choke? looks like going to ground?
3.3 uF 450V
220uf 450v

cap going to ground
coming off the power tube 100uF100v

coming off a driver tube going to ground
100uF 25v

coming off driver tube going to B+
22uF 450V

I know I shouldn't change them all. Which should I be looking at?

Thinking of going with Audyn...or Miflex

wait. am I not suppose to change the electrolytics?

thanks

 

[theflattire]

schematic



So far I'm upgrading the coupling to 0.22uF 400v to 0.22uF 630v
Not sure what else...

 

[David_NC]

I'm still relatively new to electronics / audio equipment repair and refurbishing. Below are some things I've found that help me; some have been mentioned previously.

• Take lots of pics from multiple angles. I have a USB microscope camera that has a variable brightness light and manual focus. It's excellent for getting closeups of small components like many caps and transistors, especially when they are positioned out of sight. Pics go to my PC directly, and it's quick to grab the mouse and zoom in to get a detail.
• Print out any diagrams or pics from the service manual that shows placement on the boards. I use a highlighter to mark items that will be replaced and mark the polarity with red and black Sharpies. Manuals are wrong a good bit, and this way the polarity will be known. I also like to print out specific pages of the manual, especially if there diagrams or schematics. It's easier than using a PC, though I use a one along with the printed pages. This is handy to note voltages and other details without having to type, etc.
• Presort caps for various boards into containers. I use the ones from frozen meatballs. They are Styrofoam and a lot bigger than egg containers. Leads can be poked through to keep things in place. I label each compartment or group of compartments sorted however makes sense for that project.
• Have good lighting and then some more. I don't like bright overhead lights, so I have a fairly bright one with others that can be added and positioned as needed. This also helps with reducing shadows.
• Stand-mounted magnifiers can be really useful, but cheap ones have too much distortion and make me a bit dizzy.
• Be at the correct height. I have what looks like a regular office chair but that extends about as high as a typical stool. I stand for some things, but being able to sit at just the right height that I don't bend over much makes my back happy.
• Have good tools. I don't have the best of every tool, but I have at least very good to excellent examples of the ones that I will use in almost all projects. Very small angled wire cutters are a must. Angled needle-nose pliers and hemostats are use often, too. Good strippers are def. required.
• A desoldering station is really handy! I built one but never found a suitable gun for it. I recently bought a cheap one from Amazon, and it's really impressive. It took maybe 30 seconds to desolder a 14 pin IC in a HK receiver I just repaired (with lots of help from AK members!) When I say desolder, I don't just mean I was able to remove the component; the board was completely clean, and all pads were fine, and it took maybe 5 seconds per pin. The plunger types can also be good, but the station I bought makes those feel completely archaic!

 

[davefr]

My $.02 worth.
- Buy a desoldering station. The SS-331 is good quality and affordable. Doing a recap with solder wick and/or a manual pump will be pure hell.
- It's critical to start in a known good state. Get all repairs done first.
- I like to start with dial bulb conversion to LED. Then I like to De Ox the controls which usually requires removal of the tone board. Now that the tone board is removed might as well recap it. After that I do the tuner boards since they're usually easier to recap with the tone board out of the way. After that is the driver bd. and the power supply is last. (opinions will vary)
- Triple check all your work along the way and test the unit after each sub assembly is rebuilt. Your accuracy can't be less than 100%.
- Make sure you pre-sort all your new components and which section they go in.

Some manufacturers show the board layout and traces but it's always viewed from the top down. This get's confusing since your desolder work is done on the backside. Anyone know how you can easily print a reverse image of the manufacturers layout image. It would sure be easier to reference a bottom view to find components that need to be replaced.

 

[davefr]

Maybe this trick is obvious to everyone else but I struggled trying to find component locations from the back side of the board using the diagrams/images in the service manual. These images are based on a top side view and trying to do the conversion mentally can get confusing. (and prone to error). Some image viewers have a feature called "flip". Windows Photos does not but Windows 3D Paint does under the canvas options. (along with many other free image viewers/editors) .

Copy the image from the service manual, do a flip command and now you have a much easier diagram to follow for the back side of a board.

Example: