A*P*I DOA question...

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amplexus

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So what kind of crap are they using now. I have 2 friends that have bought authentic API products in the past decade, and the 2520's in them (one just a 500 series preamp, the other one of their small consoles) the pre amp has had to have the DOA changed out at least twice. The console has had, i can't even count how many have been replaced now, especially in the master section.
I can't speak to API's practices specifically, but I've replaced dozens of the OE 2520's. I usually replace them with one of the modern reputable clones according to the customer's wishes (CAPI, Leibers' Red Dots, Whistle Rock, GAR..) Those never come back, and I've never had a negative comment on the sound or performance.
 

sr1200

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I can't speak to API's practices specifically, but I've replaced dozens of the OE 2520's. I usually replace them with one of the modern reputable clones according to the customer's wishes (CAPI, Leibers' Red Dots, Whistle Rock, GAR..) Those never come back, and I've never had a negative comment on the sound or performance.
I replaced the preamps doa with a CAPI and i haven't seen it since. The console's owner insists on using ONLY API DOA's so its cut off the legs and send a picture in to get a replacement, since just outright buying them is out of the question.
 

amplexus

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I replaced the preamps doa with a CAPI and i haven't seen it since. The console's owner insists on using ONLY API DOA's so its cut off the legs and send a picture in to get a replacement, since just outright buying them is out of the question.
I thought they'd stopped doing that... Last couple OEM API's i've bought they just sold me outright.... Maybe because I'm a commercial repair shop? Of course it has been a year or two since I mostly now convince customers to go with a non-API replacement.
 

AnalogPackrat

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Has anyone done any post-mortem analysis of the failed units? It would be interesting to know which component(s) is(are) failing. I wonder if there is something in the SMD change-over that is operating too near the margin.
 

amplexus

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Has anyone done any post-mortem analysis of the failed units? It would be interesting to know which component(s) is(are) failing. I wonder if there is something in the SMD change-over that is operating too near the margin.
Depotting them is time very time consuming. It requires heat and powerful solvents as the usual suspects- MEK, Toluene, Lacquer thinner etc... don't even make a mark on the epoxy they use. By the time you were done you'd have very little chance of determining what failed vs what was destroyed during the depotting process.
 

AnalogPackrat

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Depotting them is time very time consuming. It requires heat and powerful solvents as the usual suspects- MEK, Toluene, Lacquer thinner etc... don't even make a mark on the epoxy they use. By the time you were done you'd have very little chance of determining what failed vs what was destroyed during the depotting process.
I understand it is a challenge, but I've seen other similar devices sleuthed by determined DIYers and we have a certain member here with a long history of difficult dissections of transformers. I am firmly in the "never say never" and "can't never could" camps. SMD certainly increases the difficulty over through-hole.
 

amplexus

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I understand it is a challenge, but I've seen other similar devices sleuthed by determined DIYers and we have a certain member here with a long history of difficult dissections of transformers. I am firmly in the "never say never" and "can't never could" camps. SMD certainly increases the difficulty over through-hole.
I didn't say it was impossible- though more difficult than most potting compounds I've come across. I've depotted a few old modules or various kinds over the years to ressurect some unobtanium device, but the epoxy API uses is uniquely resilient to both chemical and mechanical attack. They're more interested in protecting whatever IP is in there and selling new modules than repairability.

But 2520's are not particularly rare, there are a dozen flavours of modern producers that nail a bunch of different variations through the years... and API still makes them by the thousands every year given that they're the core of pretty much everything they build. So other than the sheer curiosity of trying to figure out what killed a particular API 2520 (which may or may not be the same failure mode as any other dead 2520), there's no compelling reason IMO to spend the time to do it. Esp since there's unlikely to be any major mysteries in there.

I mean, hey, I'll certainly be one of the ones reading the thread if someone decides they want to have a run at it! But I am not at all surprised that no one is rushing to try and autopsy a dead 2520. My comment was less meant to be discouraging, as it was answering the "Has anyone done this before?" part.
 

MidnightArrakis

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Here is what I was able to dig up on the removal of potting compounds. And.....while the included PDF file titled, "Method For The Removal Of Thermoset Potting Compound From The Electronics Package" seems to be a sure-fire way to remove an epoxy potting compound from a circuit board.....TRUST ME!!!.....you are -- NOT -- going to like the process!!! So.....do what you may with this material, OK??? I'm just the "Messenger"!!!




dichloromethane, methylene chloride (not methyl chloride), and methylene dichloride. It boils at about 40 C or so

GOOD LUCK!!!

/
 

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  • Reworking. Removing and Decapsulating Cured Epoxy.pdf
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amplexus

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Not in the Fluoride chemistry level of bad- but DCM isn't the worlds most benign substance either! Heating a volatile, flammable, cancer causing, and acutely toxic solvent isn't my idea of a fun afternoon... But hey, I'll watch the youtube video!

Also a good point is raised in one of the linked articles with regards to using DCM or NMP solvents-
"One must also consider the materials the epoxy is bonded to if using an "epoxy dissolver". In the case of CircuitWorks Conductive Epoxy, the epoxy is usually applied directly to the surface of a circuit board. Circuit boards are made up of layers of phenolic resin-impregnated paper or epoxy resin-impregnated glass cloth (fiberglass). Any solvent that would successfully attack the cured conductive epoxy will also attack the resins that make up the circuit board, resulting in de- lamination or separation of the layers in the board. These strong solvents will also attack some metals, such as aluminum, which must be factored if the epoxy adheres to metal."


There's probably a sweet spot of time/heat/solvent where you can get the majority of the potting compound to break down, without penetrating the PCB layer enough to destroy it.
 

FIX

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I would suggest the CAPI 0252. It's the closest to the original. And as far as the whole "surface mount" thing, most good parts are now days only in surface mount. That sound isn't different. Thats just uninformed fear taking over. The only resistor that isn't available in SMD are carbon ones. They have a sound. The upside of SMD is matching and consistency.
 

JohnRoberts

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I would suggest the CAPI 0252. It's the closest to the original. And as far as the whole "surface mount" thing, most good parts are now days only in surface mount. That sound isn't different. Thats just uninformed fear taking over. The only resistor that isn't available in SMD are carbon ones. They have a sound. The upside of SMD is matching and consistency.
I remember talking with you at a trade show (last century) when you first started messing with SMD op amps.

Seems like just yesterday, but it was decades ago.

JR
 

Ike Zimbel

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It may be possible to impute what has failed from external measurements. IIRC those are pretty straightforward DOAs... Not sure what to do with that information.

JR
It's been a while, but while working on some Quad-8 (Electrodyne) MM-61 modules, I discovered that when those op-amps failed, they would read a short from, IIRC, the output pin to one of the supply pins.
 

JohnRoberts

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It's been a while, but while working on some Quad-8 (Electrodyne) MM-61 modules, I discovered that when those op-amps failed, they would read a short from, IIRC, the output pin to one of the supply pins.
That suggests a failed output stage transistor (the supply pin shorted to indicates which output device). These can fail because of over voltage punch through (like from an inductive load), or overheating. Again not sure what to do with this information as an end user.

JR
 

Ike Zimbel

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That suggests a failed output stage transistor (the supply pin shorted to indicates which output device). These can fail because of over voltage punch through (like from an inductive load), or overheating. Again not sure what to do with this information as an end user.

JR
They didn't have time to overheat, what from failing if you looked at them sideways :confused: . In retrospect, I suspect that the +/-28v supply voltage was really close to their limits (and probably always was) but there was... an expectation that these modules would be made to work at their original design voltage.
In the end, I ended up replacing most of them with a hybrid op-amp board that I got from my late friend and mentor, Neil Muncy (RIP). These had a single IC op-amp front end and a pair of discrete transistors on the output, same pin-out as a 2520 DOA. Originally, I did two of the four modules this way, which freed up enough of the original amps to do the other two. Because I didn't want to alter the boards in any way, I used a cheat to drop the voltage to each replacement module, which was a pair of 4.1v Zener diodes, backwards, as the PS leads to each hybrid amp module (these were just single sided circuit boards, not potted, no pins fitted). That knocked the supply voltage down to ~+/-23.9v, which was fine because I was using OPA604's for the chip. This worked and sounded fantastic, but after about a year the owner said that they sounded great, but different from the two with the original amps. I suspected this was due to the BiFET nature of the 604's and proposed that we sub in a bi-polar chip, in this case a 5534. Had to change the Zeners to, IIRC, 6.2v which knocked the supply to just under +/-22v (I have, somewhere a 5534 spec sheet that states +/-22v (44v) as absolute max supply voltage). Anyway, that worked a treat and the hybrid modules with the 5534 now sound indistinguishable from the originals.
 
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