still no schematic.
So ill take a wild guess C4 its a basic power supply decoupling capacitor.
so its helpful for the circuit but can be removed for now.
if its damaged would explain why the rail shows good voltage at turn on
then slowly fails downward because it looks swelled , backwards and
likely damaged. and tied across the power rail like any other decoupling cap
Far as why Q1 or Q2 dont do anything.
Again probably since every single connection and resistor going to it is a cold solder
they wont do anything.
Then ill take another wild guess that Q3 is the Vref for current source to turn on Q2.
So even if the solder was corrected on Q2
Q3 might not do anything either since it doesnt even look like
one of the legs is soldered. or has poor connections too.
So its a huge mystery why the transistor dont do anything.
Again reflow every single connection. remove C4 and likely it will work.
If it works replace C4 and of course with correct polarity
you dont want to burn up the board but the component lead and pad need heat.
very important to have a very clean soldering tip and clean it between every few welds.
with a very very clean tip. hold the tip so it touches the pad and the lead.
then when you touch the solder to it. it should instantly drink up the solder.
because both the pad and lead are hot enough.
So its a fine fine balance to have a very clean tip so the heat conducts well.
but quickly so you dont burn up the board. but its very important that the pad and lead
get very hot so the solder actually works. you could flux, but most generic solder has flux.
most the magic is always a clean clean tip and getting everything very hot so the solder works.
but very quickly so you dont burn things up.
worst case scenario, one of the output/ current source transistors is dead. with a couple DMM beep beeps with a diode
check you would know if they are dead or not
So ill take a wild guess C4 its a basic power supply decoupling capacitor.
so its helpful for the circuit but can be removed for now.
if its damaged would explain why the rail shows good voltage at turn on
then slowly fails downward because it looks swelled , backwards and
likely damaged. and tied across the power rail like any other decoupling cap
Far as why Q1 or Q2 dont do anything.
Again probably since every single connection and resistor going to it is a cold solder
they wont do anything.
Then ill take another wild guess that Q3 is the Vref for current source to turn on Q2.
So even if the solder was corrected on Q2
Q3 might not do anything either since it doesnt even look like
one of the legs is soldered. or has poor connections too.
So its a huge mystery why the transistor dont do anything.
Again reflow every single connection. remove C4 and likely it will work.
If it works replace C4 and of course with correct polarity
you dont want to burn up the board but the component lead and pad need heat.
very important to have a very clean soldering tip and clean it between every few welds.
with a very very clean tip. hold the tip so it touches the pad and the lead.
then when you touch the solder to it. it should instantly drink up the solder.
because both the pad and lead are hot enough.
So its a fine fine balance to have a very clean tip so the heat conducts well.
but quickly so you dont burn up the board. but its very important that the pad and lead
get very hot so the solder actually works. you could flux, but most generic solder has flux.
most the magic is always a clean clean tip and getting everything very hot so the solder works.
but very quickly so you dont burn things up.
worst case scenario, one of the output/ current source transistors is dead. with a couple DMM beep beeps with a diode
check you would know if they are dead or not
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Thats great.
I was able to clean up the Q2 and get the solder to flow and stick but still no action.
So I will remove Q1 and Q2 to test and compare. Using the multi meter test Q1 switch from open to 100 on the multi meter and Q2 switched from open to 300 of the multi meter. IS this with range or does it sound like Q2 needs to be replaced? I have not tested the transistor at Q3 yet.
I'll do that tomorrow. Thanks again for the help.
I was able to clean up the Q2 and get the solder to flow and stick but still no action.
So I will remove Q1 and Q2 to test and compare. Using the multi meter test Q1 switch from open to 100 on the multi meter and Q2 switched from open to 300 of the multi meter. IS this with range or does it sound like Q2 needs to be replaced? I have not tested the transistor at Q3 yet.
I'll do that tomorrow. Thanks again for the help.
If that was not clear: yes that one is defective as can be. After having seen the pictures one can conclude you have been a lucky guy for 10 years that it worked at all.
Please resolder all joints, replace resistors (these cost nil to nothing) with correct lead wire bending, replace transistors and follow advice as given. In this case it seems wise to have the device checked visually by sharp eyes here before applying power.
No. Replace all electrolytic caps (we don't know how hot these were the past decade, they're 10 years old and at least 1 was soldered in wrong), resistors and Q3/Q4 transistors in both channels. Resolder all joints with 60/40. Clean the boards meticulously and then have both channels visually checked here without applying power. The work is simply below normal quality so please first update the devices to standard quality. To avoid shameful comments and embarrassment plus many posts with too many suggestions of various (non) relevance this would really speed up things. A starting point if you know what I mean.
Not relevant right now but C3 can be replaced for a 10 µF film cap in 5mm pitch. Why one would use electrolytic caps in that position is unclear.
Not relevant right now but C3 can be replaced for a 10 µF film cap in 5mm pitch. Why one would use electrolytic caps in that position is unclear.
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just remove C4 probably work again.
it looked swelled in the picture I posted.
I missed your other post with the side view.
it pretty much barfed out the bottom. gonzo
along with very very cold solder joints
all the solder joints need to be reflowed.
on the working and non working board
im surprised DC offset was anywhere close to correct when it was working.
it is single supply so the input needs half supply ref, and half supply should be seen
on output before the dc blocking cap.
if DC on input is adjustable assume it will jump somewhere from previous
setting, since it was likely compensating for whatever voltage war was happening
before the cap blew.
remove C4 then adjust DC offset.
should work.
Re flow every joint
it looked swelled in the picture I posted.
I missed your other post with the side view.
it pretty much barfed out the bottom. gonzo
along with very very cold solder joints
all the solder joints need to be reflowed.
on the working and non working board
im surprised DC offset was anywhere close to correct when it was working.
it is single supply so the input needs half supply ref, and half supply should be seen
on output before the dc blocking cap.
if DC on input is adjustable assume it will jump somewhere from previous
setting, since it was likely compensating for whatever voltage war was happening
before the cap blew.
remove C4 then adjust DC offset.
should work.
Re flow every joint
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Here are my suggestions, everyone feel free to comment:
Ok, I understand that you want to get it working and do it right, but it’s best to be methodical. Also, while you apparently didn’t use enough heat when you built it, heating up the board enough to remove parts can sometimes damage it too. The traces can come unglued from the board. (But don’t be scared to heat parts to reflow solder or to remove them)
First order or buy a couple of rolls of “desoldering braid” in 2 sizes . Get some flux too if possible. The braid has some flux in it so probably you don’t need more to remove parts, but when reheating connections a tiny smear of flux on the blob can help.
snip out the obvious bad parts, leaving at least 1/8” or more wire stub
hold the soldering iron tip on both the remaining wire stub and and the solder on the circuit board.
Once the solder is runny, pull the wire out with pliers. It should come out easily. If not you need to heat longer. Don’t pull too hard as you can damage the board.
Now the hole in the board will probably be filled with solder. Put the end of the solder braid over the hole and the tip of the iron on top of the braid and heat it up. The solder will soak into the braid. Repeat until the hole is open enough to insert the new parts or wire.
Use the same solder braid idea to remove excess solder from any connections that are too blobby.
If the solder doesn’t flow and smooth out, (and be somewhat shiny) any connections, and add a small smear of flux and reheat.
Since you were a participant in our very first Amp Camp, I’ll get you any parts you need. It’s very important to triple check polarity.on the capacitors you replace. For resistors it doesn’t matter…
Ok, I understand that you want to get it working and do it right, but it’s best to be methodical. Also, while you apparently didn’t use enough heat when you built it, heating up the board enough to remove parts can sometimes damage it too. The traces can come unglued from the board. (But don’t be scared to heat parts to reflow solder or to remove them)
First order or buy a couple of rolls of “desoldering braid” in 2 sizes . Get some flux too if possible. The braid has some flux in it so probably you don’t need more to remove parts, but when reheating connections a tiny smear of flux on the blob can help.
snip out the obvious bad parts, leaving at least 1/8” or more wire stub
hold the soldering iron tip on both the remaining wire stub and and the solder on the circuit board.
Once the solder is runny, pull the wire out with pliers. It should come out easily. If not you need to heat longer. Don’t pull too hard as you can damage the board.
Now the hole in the board will probably be filled with solder. Put the end of the solder braid over the hole and the tip of the iron on top of the braid and heat it up. The solder will soak into the braid. Repeat until the hole is open enough to insert the new parts or wire.
Use the same solder braid idea to remove excess solder from any connections that are too blobby.
If the solder doesn’t flow and smooth out, (and be somewhat shiny) any connections, and add a small smear of flux and reheat.
Since you were a participant in our very first Amp Camp, I’ll get you any parts you need. It’s very important to triple check polarity.on the capacitors you replace. For resistors it doesn’t matter…
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It makes a lot of sense to upgrade, by adding the extra resistor that is now used in the circuit to each channel ONCE YOU GET IT RUNNING! and you’ve heated the other amp channel’s connections. There is a very complete tutorial on this simple upgrade here on the forum, that I can link to once you get to that point. Also, you should install a power supply socket on each chassis back panel It makes life easier in all ways….
Then yeah, I can recommend two Meanwell 24v power supply model numbers.( These original and the early production ACA”s were monoblocks, so require 2 supplies, but each can be smaller). Ajusting the amps for 24v is easy peasy
If you do these things the amps will be the same functionally as the most recent models!
It’s worth it! These are great amps, and you made them, and that’s pretty cool!
Mark
Then yeah, I can recommend two Meanwell 24v power supply model numbers.( These original and the early production ACA”s were monoblocks, so require 2 supplies, but each can be smaller). Ajusting the amps for 24v is easy peasy
If you do these things the amps will be the same functionally as the most recent models!
It’s worth it! These are great amps, and you made them, and that’s pretty cool!
Mark
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Good morning all. Ive been super busy with work and other pressing projects but wanted to send out a brief update to on my ACA status and say thank you. I removed the bloated cap and reheated the soldier joints and magically the amp is now producing sounds again. I am currently waiting for upgrade and replacement parts from Variac (Mark). But I am super stoked to have know that the amps will continue to serve! Regarding the reheat of the soldier joints. It was hard to get the soldier to flow in the way I know it should. I scrubbed the board with alcohol and applied a dab of flux top and bottom and using acid core soldier it worked ok some of the time but it's not as good as it should/could be. Part of me wants to keep working this angle but given the app has come back on line and my limited knowledge of how things really work I am cautious. I don't want to overheat and damage anything. Currently looking forward to the new parts coming in and adding the resister and new 24v power supplies.
