Support
Looper's Delight
|
Support |
|
|
I wrote this to Jim offline and thought it might be of use to others considering changing the resistors for EDP input/output gain. Please let me know if you find errors or confusing statements: --------- Jim, First, I want to be sure of your tools. You say soldering 'gun'. There are soldering guns, and soldering irons. Guns are usually used for heavy duty solder, and have a trigger to turn the heat on. Irons, look like a pencil, smaller tip, always hot when plugged in. You want a soldering iron, with a pointed tip. 30 watts is probably in the right power range. Too much power and you can do damage. You need a solder sucker, a spring operated device with a piston, sort of like a hypodermic needle in reverse. This will be used to remove the solder from the OLD parts, so you can pull off the OLD resistors's leads from the PCBA. Radio shack or other ectronics parts houses carry them. You need fine to medium size (diameter) ROSIN core solder, NOT acid core. Rosin core soler is designed for electronics. Acid core will destroy your pcba, in time. Need sharp wire cutters to trim the new resistors legs after soldering in place. Needle nose pliers to shape the legs of the new resistors to fit the holes, and to remove the old resistors after solder removal. The main difficulty with soldering on a PCBA is that you can overheat the thin copper foil 'trace' that is on the surface of the pcba. The edp is what is called 'through hole' pcba and components. Where a component attaches to the pcba foil trace, there is a hole. The resistor (or other electronic part) is 'stuffed' through this hole, and then soldered. If you overheat the foil trace during removal of the old part, or soldering the new part, then the foil can 'lift' off the surface of the pcba. The trace will longer stick to the pcba surface, and will often tear up to the point on the trace where the trace is still stuck to the pcba. If this happens, you must repair the trace with a small piece of wire (to substitute for the trace). Keep your soldering iron tip clean and tinned at all times (or it won't conduct heat well). Use a flat metal file, or sandpaper or emery cloth to clean the tip down to clean copper, with a good point, then tin the tip with fresh rosin core solder. Wipe the tip on a wet sponge to remove excess solder from tinning, or to clean the tip again while working. http://www.loopers-delight.com/tools/echoplex/FAQ6.html In order to replace a resistor on the EDP, you must dissasemble the EDP. I will try to step through this, but I may miss some detail, as I am not actually taking apart my edp as I describe this. MAKE SURE THE EDP HAS NO POWER CORD ATTACHED BEFORE YOU OPEN IT. BE SURE! 1. remove the top cover, there are 7 screws. Maybe different lengths, if so, pay attention to where the short ones belong. I suggest a multi compartment tray, or plastic bags to keep track of the parts you will remove. 1.5 First, inspect the parts that you think you want to upgrade. For the input and output gain modifications, it is R10 and R30 respectively. Locate these on the PCBA by reading the white silkscreened labels R10, R30. Visually, follow a line from the input jack on the back panel, towards the front panel. Before you visually reach the integrated circuit chips (Ul etc.) you will see R10. It is next to C16. R10 (iput gain) in the upgrade is 10 kilo ohms. 10kohms resistor, 1% tolerance is brown, black, black, red, brown (you may have to read it left to right, or right to left as resistors have no direction of installation for them). http://www.micro-ohm.com/colorcode/rescolor.html You can also measure the resistor in circuit with a digital multimeter (volt/ohm/miliameters), DVM. The 10 kohm resistor at R10 will read ABOUT 9.9 kohm in circuit with a DVM. If R10 is the OLD value, 2.21 kohms it will be red, red, brown, brown, brown. It will read ABOUT 2.2 kohm in circuit with a DVM. R30 location is 2 resistors to the right of R10, lined up with R10. R30 (input gain) new value is 22.1kohms which is red, red, brown, red, brown. It will read ABOUT 22 Kohm in circuit with a DVM R30 old value was 82.5 kohm which is grey, red, green, red, brown. This resistor will read ABOUT 68 kohm in circuit. You do not need to proceed if you already have the upgraded values of resistors. 2. remove all the 7 nuts on the backpanel jacks. 3. Remove the 2 screws attaching the ac power socket to the back panel. 4. If you have the old voltage regulators, you will see a metal rectangular block (heatsink) inside the back panel, between the inside back panel, and connected to 2 transistor like devices (2 voltage regualtors). This will be between the 'brothersync' jack on the back panel, and the 'ac voltage selector' switch on the back panel. 1 screw attaches the rectangular metal heatsink block to the back panel. There is a white heat conducting (but electrically insulating) grease between the heatsink and the inside back panel. It is messy and gooey, try not to get it all over you. Try to save it for when you reassemble. If there is no metal rectangular heatsink inside the back panel, then you have the new voltage regulator, that is NOT attached to the back panel. I strongly recommend the new voltage regular as it runs MUCH cooler than the old ones. 5. remove the 4 screws that hold the PCBA assembly to the bottom of the black chassis. There are 3 screws across the front edge of the pcba, and 1 near the ac power input jack. 6. remove the 4 screws that hold the white front panel to the rest of the black chassis. 7. Unless I missed a screw, the whole assembly of front panel, connected by ribbon cables to the main pcba assembly, should slide out the front or can be lifted away from the black chassis. BE CAREFUL to NOT STRESS THE RIBBON CABLES. Wires can break when bent back and forth too much. You do not want to have to repair or replace one of these ribbon cables. 8. Looking at the top of the pcba, locate the resistors that you inspected before, R10, R30. You now must identify the resistor locations on the BOTTOM of the PCBA assembly. As I recall, there are no silkscreen labels here, so this can be a bit tricky. Take you time, be sure you match the right leads to the right resistor. There are several ways to remove the old resistors. One way, if you don't mind destroying the old resistors, is to clip the resistor's leads on the TOP of the PCBA, where you can See the silkscreen label. You then can heat the remainder of the resistor's leads (from the top or Bottom of the PCBA) with the soldering iron, and pull them out while hot using the needle nose pliers. Then you must remove the remaining solder from the through holes where the legs of the new resistor will fit. Use the solder sucker to do this. First, Cock the solder sucker, so it is ready to suck. Heat the pad and hole and remaining solder until melted, and while melted place the tip of the solder sucker on the hole, and activate the sucker. It should slurp the liquid solder into the sucker. You may have to repeat this until the hole is cleared of solder. You can also use 'solder wick', but I find this is not as easy to use as a solder sucker. Also, I usually modify the tip of the solder sucker so that I can place BOTH the tip of the soldering iron, AND the tip of the sucker on the through hole AT THE SAME TIME. This modification to the tip of the sucker is just a narrow indention cut or melted into the edge of the sucker tip, Right at the front opening. It is hard to describe. After much usage, the solder sucker needs to be cleaned to remove the solder from the chamber. The tip can also clog, reducing the sucking action. DON"T OVERHEAT THE PADS OR THROUGH HOLES OR IT CAN LIFT THE PAD AND TRACES FROM THE PCBA substrate. When the hole is clean and open, you need to bend the new resistors leads at right angles to the resistor body, so that they can be inserted into the trough holes. Insert the resistor leads into the open through holes. Push or pull the resistor flush with the PCBA surface. On the BOTTOM of the PCBA assembly you will see the long, unsoldered leads of the new resistor. From the Bottom of the PCBA, position the iron tip so that it is in contact with BOTH the resistor Lead, AND the pcba pad/through hole. Apply rosin core solder to the hot pad/lead, feed enough solder to fill the through hole, and form a SLIGHT meniscus of solder on the resistor lead. Inspect the TOP of the pcba to insure that the solder wicked well. If not, reapply heat to either the top or bottom of the resistor lead/through hole and feed a bit more solder. You don't want to see Balls of excess solder, just a good, wet coverage of the pad and lead. MAKE SURE that no excess solder creates a circuit path or bridge to other pads or traces as this will cause malfunction. TRIM the excess lead from the BOTTOM of the PCBA assembly for R10 so that the leads CANNOT short out on the bottom chassis. Trim the leads to the approximate lenght of all the other resistors on the PCBA. Repeat process of removal, cleaning hole, soldering for R30. Visually inspect your work again to insure a good, wet solder job, and no shorts from excess solder, and that you cut the excess resistor leads short enough. Reassemble in reverse order. Test, debug, repair as required. I think this is pretty complete, but since I have not followed exactly what I typed I cannot say there are no errors. Please write if you have questions or comments. regards, bret --- JIMFOWLER@prodigy.net wrote: > bret- > > i've done plenty of cable soldering, so i'm pretty > handy with a soldering gun but i've never worked on a > pcb. > > i've got a 30-watt gun and some 60/40 solder. if i > get in there and think i might do more damage than > good, i'll back out. that having been said, if you > could give me a walkthrough, i'd appreciate it. > > -jim > __________________________________________________ Do You Yahoo!? Yahoo! Health - Feel better, live better http://health.yahoo.com