Hi all
First post around these parts.
Got a Studio .22 in for repair which as a number of issues.
Its been got at in the past so some less than ideal looking work has been done.
Its had the usual graphic EQ dropping out issues with the O/C 1k resistor in the foot switch supply, this one has been modded as per .22 plus on that front.
The remaining issues now with it is a intermittent cracking noise that's set off with vibration or tapping around the PCB.
I thought it was down to a socket issue on V2 which i have replaced but the problem is still there.
Im thinking it might be something to do with a rail somewhere as ive also found a few high value droppers, the 10K (R123) and 5.6K (R132)
Swopped out all the valves now and no change.
Is there any known problems with this amplifier chassis that can cause this problem?
Thanks
Boogie Studio .22 Repair
Moderators: pompeiisneaks, Colossal
Re: Boogie Studio .22 Repair
i had one on the bench last year with a similar issue I touched up all the solder points and cleans the the pots and tube socket pins. I also replaced the preamp tubes, as they tested low. The amp fired up nicely.
My Daughter Build Stone Henge
Re: Boogie Studio .22 Repair
Hi thanks for the reply.
Found a number of dry joints forming around the valve sockets and other areas, re-flowed those but problem is still there.
l'll try cleaning the output and phase splitter sockets a, ive only done the input stages and reverb drive.
I need to replace a number of resistors to get the rails a bit closer to spec so really need to flip the board over which is a pain.
I thought the problem was around the input stage somewhere but now im not so sure, its being a right pain to track it down.
Ive run it up with stages disconnected to try and isolate where its happening, but when i think ive found it problem comes back.
What sort of power output should i expect? i measure around 33V p/p into 10R so around 13W rms, is that a bit low for one of these?
Most EL84 pushpull designs seem to be in the 10 - 15W output range so might not be too far out.
I still need to check screen resistors and other in the output stage..
Thanks
Found a number of dry joints forming around the valve sockets and other areas, re-flowed those but problem is still there.
l'll try cleaning the output and phase splitter sockets a, ive only done the input stages and reverb drive.
I need to replace a number of resistors to get the rails a bit closer to spec so really need to flip the board over which is a pain.
I thought the problem was around the input stage somewhere but now im not so sure, its being a right pain to track it down.
Ive run it up with stages disconnected to try and isolate where its happening, but when i think ive found it problem comes back.
What sort of power output should i expect? i measure around 33V p/p into 10R so around 13W rms, is that a bit low for one of these?
Most EL84 pushpull designs seem to be in the 10 - 15W output range so might not be too far out.
I still need to check screen resistors and other in the output stage..
Thanks
Re: Boogie Studio .22 Repair
have you tested the caps for leakage?
You may also have a bad resistor, similar to the 100K resistors that go bad on the fender blackface in the preamp section. You are going to most likely need to remove the board completely to service the amp. You are using known good tubes?
13w is probably ok it depends greatly on the tubes themselves, brand, etc. as long as your voltages are safe and the tubes are biased within operating tolorance it is what it is.
have you cleaned your potentioments? caig fader lube.
make sure all your bolts screws and nuts are tightened down snug.
Can you recreate the issue every time or is it hit and miss? You should be able to signal trace and or tone generator and scope though the amp and isolate the section with the problem.
You may also have a bad resistor, similar to the 100K resistors that go bad on the fender blackface in the preamp section. You are going to most likely need to remove the board completely to service the amp. You are using known good tubes?
13w is probably ok it depends greatly on the tubes themselves, brand, etc. as long as your voltages are safe and the tubes are biased within operating tolorance it is what it is.
have you cleaned your potentioments? caig fader lube.
make sure all your bolts screws and nuts are tightened down snug.
Can you recreate the issue every time or is it hit and miss? You should be able to signal trace and or tone generator and scope though the amp and isolate the section with the problem.
My Daughter Build Stone Henge
Re: Boogie Studio .22 Repair
Hi
Not checked the supply caps yet as i still need to flip the board over, i was trying to do as much fault finding as possible with it all in place.
Found few high value dropper resistors and new replacements are on the way. l'll do the screen resistors while im there.
Have cleaned the pots with Craig fader lube as it goes.
The pops and crackling happens when you tap the chassis, it comes and goes, the amp itself is basically working when into a dummy load / signal gen.
Im just going to have to get to the other side of the board and go through the lot, it will be quicker than trying to fault find with the way it is.
I think its an issue with the H.T somewhere, i think i saw the interference on the lower 300V rail. Ive only fitted the second preamp valve, FX loop buffer, phase splitter and outputs to try and narrow it down a bit.
I did think the problem was around V2 but that proved not to be the case..
l'll check all the ground points and joints as you say, im sure it will be obvious when i eventually find it. Its just the time getting there...
Cheers
Not checked the supply caps yet as i still need to flip the board over, i was trying to do as much fault finding as possible with it all in place.
Found few high value dropper resistors and new replacements are on the way. l'll do the screen resistors while im there.
Have cleaned the pots with Craig fader lube as it goes.
The pops and crackling happens when you tap the chassis, it comes and goes, the amp itself is basically working when into a dummy load / signal gen.
Im just going to have to get to the other side of the board and go through the lot, it will be quicker than trying to fault find with the way it is.
I think its an issue with the H.T somewhere, i think i saw the interference on the lower 300V rail. Ive only fitted the second preamp valve, FX loop buffer, phase splitter and outputs to try and narrow it down a bit.
I did think the problem was around V2 but that proved not to be the case..
l'll check all the ground points and joints as you say, im sure it will be obvious when i eventually find it. Its just the time getting there...
Cheers
Re: Boogie Studio .22 Repair
have you tried running the amp while it's open and touching through the circuit with a chopstick and forcing the amp to crackle as you probe? then address that solder point / component?
My Daughter Build Stone Henge
Re: Boogie Studio .22 Repair
Yes exactly that, seemed very sensitive around V2 area to the point that i changed the socket after trying to clean and re-tension the contacts.
I was starting to think a component issue, i tried a few around that area but it still played up.
Ive also fitted a another set of tubes, same problem.
Remade most of the joints now on the board, just not around the graphic EQ section yet but they looked ok..
I think im going to see how things are after changing the 10K dropper for the ECC83's and the 5.6K from the main HT rail.
I bet its a component with a hairline crack or fracture or a joint on the underside of the board that i haven't seen yet.
I was starting to think a component issue, i tried a few around that area but it still played up.
Ive also fitted a another set of tubes, same problem.
Remade most of the joints now on the board, just not around the graphic EQ section yet but they looked ok..
I think im going to see how things are after changing the 10K dropper for the ECC83's and the 5.6K from the main HT rail.
I bet its a component with a hairline crack or fracture or a joint on the underside of the board that i haven't seen yet.
Re: Boogie Studio .22 Repair
Gonz - I don't know exactly what the schematic is of your MB but I have a .50 cal + that has an effects loop that is bypassed by a NC contact on one of the 1/4" jacks when the loop is not used. This NC connection went bad on my amp and caused a bunch of intermittant noise. If your amp has an effects loop you might look into this...
Effect Loop contacts
bad solder joint or funky effects loop
you could plug into the loop return bypassing the v2 tube and see if the problem is still there
http://www.schematicx.com/schematic/mes ... schematic/
you could plug into the loop return bypassing the v2 tube and see if the problem is still there
http://www.schematicx.com/schematic/mes ... schematic/
There's no fool like and old fool
Re: Boogie Studio .22 Repair
My DC-3 also started to have the same problem, which was fixed with exactly this same procedure.selloutrr wrote:i had one on the bench last year with a similar issue I touched up all the solder points and cleans the the pots and tube socket pins. I also replaced the preamp tubes, as they tested low. The amp fired up nicely.