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Repair base

Repairs of XTA DP processors, battery replacement

dealing with battery corrosion.

XTA DSP, Digital Sound Processors and specifically the DP200 and DP202 are excellent DSP’s, clean sound and very versatile in the format a 2 in, 4 out or 2 in, 2 out processor. Capable of providing control characteristics with powerful equalisation, time delay, limiting, level control and, as the product has become known for later, able to act as a loudspeaker crossover, processor.

The main software is held in a non volatile memory and in the case of DP200 and DP202 the software versions are 4.02 and 4.01 respectively. No further updates have been done after this as the units are now a “legacy” product. Which is a shame because these are excellent, versatile DSP’s which can be used for matrixing, distribution and control as well as crossovers and offer remote control via RS485, RS232 (single unit at a time) and Midi (short distances). The RS485 is able to communicate over paired cables such as multicore and microphone cable over long distances via the Audiocore version 6 software which is the last version of remote PC software to support DP200/202 processors.

The programmable memory, using parameters entered or altered from the main core software settings are held in a volatile memory of 40 memory slots supported by a rechargeable NiMh 3.6v battery which in most cases is a Varta V80h. There are others similar and these cost more than most but the parameters especially temperature range make this the best type. After non or low use or when the unit is aged (five years or more) this battery fails spectacularly by releasing acid, generally from the negative end of the battery which if not caught in enough time can eat into the circuit board. The circuit board is of excellent construction using a glass fibre base it uses several layers of connectivity on top, bottom and with a central ground plane internally. The tracks on the board are quite fine and several of the main front to back circuit tracks run under this battery and can be damaged or eaten away by the battery acid spilling out from a dead battery if left to long.

It cannot be stressed how important it is to a) back up the memories/settings on a regular basis and b) Check at least once per year internally by taking the lid off to see if any sign of “furring” or leakage on either end of the battery is occurring.

The picture below shows the top of the DP unit with lid off, battery is blue in the middle and the detail of track that runs under the battery is clearly shown. This battery has leaked you can see a white fur of dried acid on the negative terminal.

To change the battery you need clear work bench space, good quality soldering iron, then 18 gauge resin cored leaded solder, a solder sucker or solder removal tool/iron and a battery. If you have had bad battery leakage you will need IPA/Circuit board cleaner, cotton buds, abrasive pen, fine tinned wire and TVR board sealer. To start remove lids on both top and bottom, the lower lid is also supporting the circuit board with three PCB stand offs, some times these are not attached as the adhesive dries off but if they are still attached the lid wont come away, if this is the case don't pull, the last thing you want to do is stress the circuit board, a small pair of snipe nose pliers can be used to push the locking plastic clip in between the two uprights and ease the board off the clips.

The bottom of the DP unit, showing the three stand offs (white squares) on the right a close up showing the three battery solder pads under the circuit board

Once both lids are removed place the DSP upside down on the work top and using the soldering iron and solder sucker quickly heat and suck each of the three joints, at first you may not remove all the solder, don't worry, now re-solder each of the three joints, yes! Add new solder to the joint and repeat the heat and de-solder, this time the solder will come off better, its worth remembering that on most solder joints putting on more new solder will help remove solder. Keep heating on the board to a minimum otherwise the tracks will lift from the board as the size of the track is small and the heat can soon destroy the adhesive holding the track to the board.

Turn the DSP over and position it so you can lift the twin pad “plus” side of the battery while heating with the iron. Apply heat and lift each side of the plus end of the battery easing a little bit at a time, this is a slow process but it needs to be otherwise you may rip the track off. Once clear it leaves just the minus end to release. If it is a straight battery change, heat the minus end and slowly and carefully ease out the battery. Once removed apply clean solder again to the now empty hole and suck/clean out, offer up replacement battery and ease into place. Turn the DSP back over and solder the battery into place leaving heat on for a fraction longer than a single sided work board which allows the solder to flow through. Make sure the battery is properly in place and the pins are protruding through.

If its a battery that has leaked then the minus side would be furred over and this stops the iron from heating the solder on the contact. Use a cotton bud soaked in IPA to clean as much of the furring off the contact as possible. Once clean use the abrasive pen to clean a point on the battery contact as near to the board as possible but not the board itself, this helps keep the heat from the track on the board as you work the battery out. Do this by heating and applying solder to this contact so that the heat from the iron travels into the battery contact and then to the solder on the board. Using the same system as the other end ease and heat, perhaps with a slight twist each time until the battery comes away. The acid will be on the circuit board track pad for the minus end of the battery and this will be a dark grey because of oxidation. This will not solder and needs to be prepared by using a flux only pen or at worst an abrasive pen and remove the oxide then re-heat and solder to tin, sucking any excess away before fitting the battery.

Thie picture on the left shows a battery has leaked and you can see the furr (dried acid) of the acid on the end in other photographs above. Shown here is it being removed using IPA Circuit board cleaner and a cotton bud to clear the contact enough to get the heat from a soldering iron to melt the last bit of solder holding the battery in.

 The picture on the right shows a small acid spill from a battery prior to cleaning and in the picture below we are cleaning the surface off with a bud and IPA, after a good swab round we polish the surface off removing as much of what we applied with hopefully all of the corrosive acid. Sometimes you may have to wash a large area using a small brush and IPA or circuit board cleaner and then carefully swab round to remove all contaminants.

Its at this point you need to assess the damage, if you have caught the corrosion in time then you can use IPA on cottons buds or even on a small paint brush and clean round the circuit board to remove spilt acid and dry paper cloths or cotton buds to just make sure every bit of acid is mopped up. If the board is good at this point then fit a new battery, if there is track damage then we need to do the following, use IPA to clean over and around the tracks that are damaged, take note of which tracks go to where on the board before removing the damaged tracks in each direction until the track is solid (generally un-exposed under original varnish). Expose the ends of these solid tracks using the abrasive pencil and using solder, tin the tracks, this may require several quick applications of heat and solder and then remove. Once a smooth solder pad is made tin the end of the thin tinned copper wire and attach to one of the track/pad ends, using miniature screwdrivers and small pliers, carefully position and shape the tinned wire following the original route of track until it reaches the other track end also made as a solder pad, cut to length (I use scissors to cut to avoid stressing) do the same for the other damaged tracks and once done check, straighten and position then apply TVR to hold the tinned wire repairs and seal the board again. After this fit a new battery.

This picture shows a new battery in place with board cleaned.

A version of this repair is to fit small uprights of wire in the battery position to which a new battery can be attached meaning that it is easier and simpler to change the battery in the future without disturbing the board or indeed removing the bottom cover. We have tried this successfully and it is a much quicker process.

In the case of severe damage sometimes the new battery may have to be repositioned which we have done on some occasions. If you want help with any of the information contained within at any time then get hold of us, details are on the contact page. This last picture shows our cleaned PCB layered with TVR to create a seal that the corrosive acid cannot get through.

Finally power the DP unit up. It will display “Battery Failed” and red lights flash side to side. Press a button to reset, it will flash slowly and say disconnect all outputs. Press any button again and it will stop flashing and go to a basic setting. If you wish to re-load your saved settings use the “Cloning XTA DP 200” in the Juice S&L information page.

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