Happy Friday!
I know, I know.. elongated lull. Apologies. Expect more of the same...
..for now.
Showing posts with label corrosion. Show all posts
Showing posts with label corrosion. Show all posts
Friday, September 13, 2013
Thursday, November 03, 2011
Bought a Zoom H4 in "doesn't power on" condition at auction. It arrived yesterday, loose in a small priority mail box. I guess a demonstration on how robust these things are was in order.
I cracked the compartment lid and had a peek at the battery terminals; sure enough, this thing was stored with batteries installed and a chemical reaction had taken place.
First item of business is to crack the shell. Removed the two visible screws (the lower one was behind a press fit rubber plug) and felt a screw sized indention behind the product label. In punching through the label to investigate, I can report that indention is a casting mark and can be left alone, there are only two screws on the back half of the shell.
The front & rear halves of the enclosure are snap fit together. Pictured are the three major points: above "LINE" (which is easy as you can slide your finger into the battery compartment and pull that one right out, I saved it for last), above "USB" and at the halfway point of the bottom silver case halves. Once the bottom was freed, the USB connection followed, allowing me to ease the LINE connect open from the battery compartment. Other side is similar, but only one side needs to be unlocked to separate the case halves.
The corrosion here effectively insulated the battery stack, rendering the unit inoperable. I believe the foam blocks are there to prohibit side to side movement of the contact spring, and are therefore important to retain.
Removal of the contact is easy: pliers on the elbow at the base of the spring will allow you to pull this part out when the solder is liquified. Referring to the image of the corroded contact in place, the solder pad is the entire joint as seen at upper right of the image.
I used a little universal solvent and these cleaned right up. I did pick at the spring a little to free larger chunks of the crystalline build up, but for the most part minimal agitation was required.
While the parts were out to wash I did a quick pass on the battery compartment with a wet rag.
Battery door flap back in place just before snapping the rear case half back into place & returning the hardware to its original position.
I'm happy to report the unit works like a champ now. All in all I think the entire span of time spent on this was about a half hour, including stopping to take pictures or reprimand my two year old assistant.
Sunday, January 16, 2011
I washed the upper PCB of the ART DR-X effects unit today. This process consisted of the following tools:
One used toothbrush (largely defunkified through prior use with isopropyl alcohol), one 8x10 photo developing tray, one gallon of distilled water (of which approximately one pint was used here), an air compressor and a heat gun.
I pulled the following shot from the previous write-up:
Since chemistry isn't my strong point, I can only guess that the white chemical growth at the legs of the pins is caustic potash. Therefore, I reason that a mild detergent is probably not required, since the caustic nature of the build up is going to provide more "cleaning" power than I probably need to begin with.
I poured enough distilled water to just cover the top of the ICs, and before agitation a considerable amount of the white build up dissolved. After 30-40 seconds with the brush, I hit the PCB with compressed air to disperse most of the water, then followed up with the heat gun. In order to avoid overheating the PCB, I held it by hand while distributing heat (which was a huge motivator to keep that gun moving). The idea behind the heat gun is to encourage evaporation of moisture remaining after the compressed air.
Something had been bothering me about the source of the saponification; in the past when I've seen this build up it has been localized (or at least centered around) a decomposing battery or electrolytic capacitor. This was distributed more or less evenly across the entire PCB, moreover the back-up battery and capacitors did not exhibit any of the build up.
An aspect of metallurgy is that dissimilar materials will often facilitate corrosion at contact points. In comparing before and after wash pictures, I can't help but notice that a good portion of the build up is centered on joints that were not completely filled in the soldering process.
A closer inspection of the lower, largely digital board reinforces the theory that the poor infill is, if not the root source of the failure, at least largely contributing to the problem. By the mid to late 1990s I recall that ART effects from the earlier part of the decade had gained a reputation of unreliability, which leads me to wonder if the chemical build-up around the legs, which certainly may have been allowing functionally disruptive crosstalk, wasn't isolated to this unit alone.
Perhaps I'll trip over some similar era non-functional ART units upon which to test this theory.
I'll need to grab a larger tray to wash that board though, so this process remains in a state of limbo.
One used toothbrush (largely defunkified through prior use with isopropyl alcohol), one 8x10 photo developing tray, one gallon of distilled water (of which approximately one pint was used here), an air compressor and a heat gun.
I pulled the following shot from the previous write-up:
Since chemistry isn't my strong point, I can only guess that the white chemical growth at the legs of the pins is caustic potash. Therefore, I reason that a mild detergent is probably not required, since the caustic nature of the build up is going to provide more "cleaning" power than I probably need to begin with.
I poured enough distilled water to just cover the top of the ICs, and before agitation a considerable amount of the white build up dissolved. After 30-40 seconds with the brush, I hit the PCB with compressed air to disperse most of the water, then followed up with the heat gun. In order to avoid overheating the PCB, I held it by hand while distributing heat (which was a huge motivator to keep that gun moving). The idea behind the heat gun is to encourage evaporation of moisture remaining after the compressed air.
Something had been bothering me about the source of the saponification; in the past when I've seen this build up it has been localized (or at least centered around) a decomposing battery or electrolytic capacitor. This was distributed more or less evenly across the entire PCB, moreover the back-up battery and capacitors did not exhibit any of the build up.
An aspect of metallurgy is that dissimilar materials will often facilitate corrosion at contact points. In comparing before and after wash pictures, I can't help but notice that a good portion of the build up is centered on joints that were not completely filled in the soldering process.
A closer inspection of the lower, largely digital board reinforces the theory that the poor infill is, if not the root source of the failure, at least largely contributing to the problem. By the mid to late 1990s I recall that ART effects from the earlier part of the decade had gained a reputation of unreliability, which leads me to wonder if the chemical build-up around the legs, which certainly may have been allowing functionally disruptive crosstalk, wasn't isolated to this unit alone.
Perhaps I'll trip over some similar era non-functional ART units upon which to test this theory.
I'll need to grab a larger tray to wash that board though, so this process remains in a state of limbo.
Tuesday, January 04, 2011
I've depleted my stash of basket case amplifiers on hand, so it's time to crack the case on that Peavey 260. Don't worry, there are plenty of basket case amplifiers and so forth that will be looked at in the future, I just have to dig them out.
Access to amplifier transistors is about as easy as it gets. My original hunch on this amp, that carried 39 volts DC on the signal pin of the output jack, was that of a failed power transistor. These all tested good, so my suspicion has been downgraded to failed driver pushing the output into saturation or good old fashioned funkiness with the connections.
These sockets may have to go. I'm weighing out my abilities to polish/inspect the connector surface, while my mind keeps interjecting "remove and replace". Honestly, circuit analysis while charged seems pointless while these sockets are cradling the pins of the output devices. I should also mention that the pins on the TO3 transistors are also less than pristine, almost as if something has been electrochemically corroding them.
The power supply capacitors are clearly in need of replacement, physical distortions are evident.
I also don't approve of the mains ground termination, pictured here tying in with the sleeve of a speaker output jack. This makes for a completely mechanical joint, relying on the nut that holds the jack in place to complete ground. I'm guessing, if you're reading this, that you are familiar with these nuts of which I speak. They wouldn't be my first choice for a safety feature, but this isn't the work of Peavey, it is a retrofit to three prong from the OE two prong power cable. Better than nothing I guess, I'll still change it to satisfy my standards.
Access to amplifier transistors is about as easy as it gets. My original hunch on this amp, that carried 39 volts DC on the signal pin of the output jack, was that of a failed power transistor. These all tested good, so my suspicion has been downgraded to failed driver pushing the output into saturation or good old fashioned funkiness with the connections.
These sockets may have to go. I'm weighing out my abilities to polish/inspect the connector surface, while my mind keeps interjecting "remove and replace". Honestly, circuit analysis while charged seems pointless while these sockets are cradling the pins of the output devices. I should also mention that the pins on the TO3 transistors are also less than pristine, almost as if something has been electrochemically corroding them.
The power supply capacitors are clearly in need of replacement, physical distortions are evident.
I also don't approve of the mains ground termination, pictured here tying in with the sleeve of a speaker output jack. This makes for a completely mechanical joint, relying on the nut that holds the jack in place to complete ground. I'm guessing, if you're reading this, that you are familiar with these nuts of which I speak. They wouldn't be my first choice for a safety feature, but this isn't the work of Peavey, it is a retrofit to three prong from the OE two prong power cable. Better than nothing I guess, I'll still change it to satisfy my standards.
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