Hi there,
My carlsbro cobra 90 twin stayed in the (dry) basement for a decade or so. Now, when I plug my guitar in, I have to push the High gain input pot 100% and the reverb gain some 80% and then slowly increase the master volume while playing to wake the loudspeaker up. Once awaken I can lower the volume to a more decent level. Everything stays OK as long as I don't stop playing. If I stop for 3-5 seconds, the amp starts to distord the sound (sort of a dying saturation) and then goes back to mute until I push the master volume up again (while playing). The power amplifier seams to be OK. It's the signal processing that looks defective. Pots and Jacks are OK. There are two removable ICs (one being a CD4016BE and the other I don't remember). Both have been removed and cleaned (they were clean anyway) and put back into place with no improvement The CD4016BE has been temporarily replaced with a MC14066BCP (an equivalent) with no improvement. All capacitors look OK (from a leakage point of view) as well as the PCB and wiring. Does any of you have the schematic drawing of this board ? Or any clue ?
Thanks
My carlsbro cobra 90 twin stayed in the (dry) basement for a decade or so. Now, when I plug my guitar in, I have to push the High gain input pot 100% and the reverb gain some 80% and then slowly increase the master volume while playing to wake the loudspeaker up. Once awaken I can lower the volume to a more decent level. Everything stays OK as long as I don't stop playing. If I stop for 3-5 seconds, the amp starts to distord the sound (sort of a dying saturation) and then goes back to mute until I push the master volume up again (while playing). The power amplifier seams to be OK. It's the signal processing that looks defective. Pots and Jacks are OK. There are two removable ICs (one being a CD4016BE and the other I don't remember). Both have been removed and cleaned (they were clean anyway) and put back into place with no improvement The CD4016BE has been temporarily replaced with a MC14066BCP (an equivalent) with no improvement. All capacitors look OK (from a leakage point of view) as well as the PCB and wiring. Does any of you have the schematic drawing of this board ? Or any clue ?
Thanks
Lots of times when instruments sit around the connections oxidize. The is any tin or brass plated connector. usually you remove them and put them back will scrape the oxide off. If not, some designs you can rub with an abrasive pink pearl eraser then wash clean with alcohol. The IC is one such connector, but a 4016 is a switching IC, not a linear part. The lower voltage areas are the most subject to oxide insulation. Usually the 24 V or higher power amp with significant current will burn the oxide off the connectors in that area after a few minutes use.
Long term, gold plated connectors in the low voltage areas are really nice. I'm replacing a few low voltage tin plate pins on the VI limiter circuit of my PV-1.3k with gold.
If you want to check your power supplies usually they are about 80% of the rating on the filter capacitor near the rectifier.
Long term, gold plated connectors in the low voltage areas are really nice. I'm replacing a few low voltage tin plate pins on the VI limiter circuit of my PV-1.3k with gold.
If you want to check your power supplies usually they are about 80% of the rating on the filter capacitor near the rectifier.
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A VERY, VERY common fault with Carlsboro units (ans presumably others) was simply dirty switch contacts on the jack sockets - in particular the ones for effect insertion.
A quick squirt of WD40 in the sockets, and push a jack plug in and out a few times often cures it.
It's sad to see the demise of Carlsboro, it was decently made gear, and was made only a few miles from where I live - they also happily sent you schematics and spares if you asked.
A quick squirt of WD40 in the sockets, and push a jack plug in and out a few times often cures it.
It's sad to see the demise of Carlsboro, it was decently made gear, and was made only a few miles from where I live - they also happily sent you schematics and spares if you asked.
Hello Nigel,
WD40? Not recommended. It leaves a greasy film on the contacts.
Use a decent contact cleaner; there are plenty available.
About the schematics for Carlsbro...
If they are made before the current owner took over the company then you do not even get a reply from them.
Sad I must say.
If you know a good site where to find them, It makes me happy.
Hi JagV12,
1. Is there a preamp out and a power amp in?
2. Can you then apply a signal of sufficient level in to the power amp in?
Is it loud enough?
3. Then can you couple the preamp out to another poweramp?
Is it ok?
This way we can find out where the problem lies.
In the preamp, the poweramp or the power supply.
Let us know.
WD40? Not recommended. It leaves a greasy film on the contacts.
Use a decent contact cleaner; there are plenty available.
About the schematics for Carlsbro...
If they are made before the current owner took over the company then you do not even get a reply from them.
Sad I must say.
If you know a good site where to find them, It makes me happy.
Hi JagV12,
1. Is there a preamp out and a power amp in?
2. Can you then apply a signal of sufficient level in to the power amp in?
Is it loud enough?
3. Then can you couple the preamp out to another poweramp?
Is it ok?
This way we can find out where the problem lies.
In the preamp, the poweramp or the power supply.
Let us know.
Thank you all,
I think you're right, oxidized contacts is probably the cause of this malfunctioning. Yes Tarzan, there is a preamp out and a power amp in. I used my PC audio out to test the power amp and it works 100% (ask the neighbors !). As the main vol pot has an effect on solving the problem, I guess the faulty contact is beyond the preamp output and as it is before the power amp input, it should be that Effect Loop pair of auto-cut-off jacks that need a cleanup. Carlsbro answered my email but they don't have the schematics for this device.
I'll try the cleanup as soon as I can. Is there a Button (or whatever) to mark this thread as "Solved" (as soon as it will be)?
I think you're right, oxidized contacts is probably the cause of this malfunctioning. Yes Tarzan, there is a preamp out and a power amp in. I used my PC audio out to test the power amp and it works 100% (ask the neighbors !). As the main vol pot has an effect on solving the problem, I guess the faulty contact is beyond the preamp output and as it is before the power amp input, it should be that Effect Loop pair of auto-cut-off jacks that need a cleanup. Carlsbro answered my email but they don't have the schematics for this device.
I'll try the cleanup as soon as I can. Is there a Button (or whatever) to mark this thread as "Solved" (as soon as it will be)?
Hi Guys
Apart from contacts on switches and effects loop jacks oxidising, the main issue with repowering idled equipment is filter cap health.
Electrolytic caps are made using an electric oxidation process (called "forming") to create the dielectric. This dielectric requires regular application of voltage to stay healthy. An amp that has sat unpowered for ten years can easily blow the fuse upon power up as the caps have "de-formed". Best to repower slowly to reform the electrolytics safely. But... you are past that point now.
Anyway, as a reminder to anyone who collects amps or has a collection of equipment:
Power it up for twenty minutes every week to keep the caps healthy.
Many guys with tube amp collections pull something out of the closet every six months and find the amp to be temperamental and sputtery. They put it back for another six months. This is no way to treat equipment. Were those amps powered regularly, the only variation of tone would be from the tubes themselves.
NEVER use WD-40 on electronic equipment. It is corrosive and will eat the inside of pots and anything plastic.
ONLY use sprays, cleaners and lubes INTENDED for electronic equipment.
Have fun
Kevin O'Connor
Apart from contacts on switches and effects loop jacks oxidising, the main issue with repowering idled equipment is filter cap health.
Electrolytic caps are made using an electric oxidation process (called "forming") to create the dielectric. This dielectric requires regular application of voltage to stay healthy. An amp that has sat unpowered for ten years can easily blow the fuse upon power up as the caps have "de-formed". Best to repower slowly to reform the electrolytics safely. But... you are past that point now.
Anyway, as a reminder to anyone who collects amps or has a collection of equipment:
Power it up for twenty minutes every week to keep the caps healthy.
Many guys with tube amp collections pull something out of the closet every six months and find the amp to be temperamental and sputtery. They put it back for another six months. This is no way to treat equipment. Were those amps powered regularly, the only variation of tone would be from the tubes themselves.
NEVER use WD-40 on electronic equipment. It is corrosive and will eat the inside of pots and anything plastic.
ONLY use sprays, cleaners and lubes INTENDED for electronic equipment.
Have fun
Kevin O'Connor
Thank you all,
Carlsbro answered my email but they don't have the schematics for this amp. Thinking it over, Struth is right, it should be the Effect Loop jacks that cause the problem as the power amp works flawlessly with my PC audio out (ask the neighbors !) and the main vol pot (last element in the audio processing chain) has a major effect on solving the problem.
Thanks for the tips (WD40 prohibited and Electrolytic caps issue).
Am I supposed to mark the thread as "Solved" (once done) ? How do I do that ?
Carlsbro answered my email but they don't have the schematics for this amp. Thinking it over, Struth is right, it should be the Effect Loop jacks that cause the problem as the power amp works flawlessly with my PC audio out (ask the neighbors !) and the main vol pot (last element in the audio processing chain) has a major effect on solving the problem.
Thanks for the tips (WD40 prohibited and Electrolytic caps issue).
Am I supposed to mark the thread as "Solved" (once done) ? How do I do that ?
That's the reason for using it - it leaves a layer of lubrication on the contacts, protecting them and encouraging good contact.
None work as well as WD40, I've been using it professionally for over 30 years, and it out performs all the specific 'electrical cleaners'.
It's particularly good on pots, which are supposed to have lubricant in them, which normal switch cleaners wash away.
I don't know where Kevin gets the idea it's corrosive?
in over 30 years I've never had a problem with it, nor have other engineers here.What you must NEVER do (obviously) is squirt it blindly in a VCR or cassette player, those it will destroy, as they work on friction.
Hi Guys
Nigel, are you letting UK frugality guide you down a ruinous path?
WD-40 EATS those VCR parts - it is not just a friction issue. It also eats the carbon tracks in pots. Do you also use that carburetor cleaner Diaz recommended to shine up tolex? Just because both those recommendations appeared in a popular book - along with a lot of other misinformation - does not make it true.
Have you ever used 'Blue Stuff'? It lubricates and cleans but is not thin enough to wick into nominally sealed components.
Have fun
Kevin O'Connor
Nigel, are you letting UK frugality guide you down a ruinous path?
WD-40 EATS those VCR parts - it is not just a friction issue. It also eats the carbon tracks in pots. Do you also use that carburetor cleaner Diaz recommended to shine up tolex? Just because both those recommendations appeared in a popular book - along with a lot of other misinformation - does not make it true.
Have you ever used 'Blue Stuff'? It lubricates and cleans but is not thin enough to wick into nominally sealed components.
Have fun
Kevin O'Connor
It simply coats everything in a thin cost of oil, it doesn't 'eat' anything
I've never seen it 'eat a carbon track' either, in more than 30 years of using it in that way.
Hi Guys
JagV12, glad your amp is working now!
NG, my comments are based on the experience of many techs I know who service all the said items above. If your experience with WD-40 is more positive, then you are the exception that makes the rule. See how unique and special you are? Thanks!
Everyone else should avoid WD-40 mixed with electronics.
As a water displacement chemical - which is what WD stands for - it is great. It is almost okay for lubricating squeaky things but regular machine oil works much better.
I found the perfect way to not see things is to look the other way. Or use your wonky eye.
Have fun
Kevin O'Connor
JagV12, glad your amp is working now!
NG, my comments are based on the experience of many techs I know who service all the said items above. If your experience with WD-40 is more positive, then you are the exception that makes the rule. See how unique and special you are? Thanks!
Everyone else should avoid WD-40 mixed with electronics.
As a water displacement chemical - which is what WD stands for - it is great. It is almost okay for lubricating squeaky things but regular machine oil works much better.
I found the perfect way to not see things is to look the other way. Or use your wonky eye.
Have fun
Kevin O'Connor
I haven't seen WD40 be corrosive, and I frequently use it as a preservative. It's very effective at protecting steel from water.
But I never use it on electronics either. For electronics I want a cleaner or cleaner with lube, for different uses. With lube should be a lube like silicone or something that doesn't thicken over the years. WD40 definitely thickens over time. On the other hand, some mfgrs purposely use thick "lube" to make pots seem more "substantial". For instance many Tapco mixers have immobilized pots after a decade of non-use, but clean up to work fine. What you really don't want IMHO is anything like a penetrating oil, which is purposely designed to apply thin and capillary into tight spaces, then turn into thicker grease.
I clean with carbon tetra cloride or carbon tri chloride. I like the Caig products (pretty large line of conductive and non-conductive cleaners, lubes, and preservatives) and used Cramolin I think it was called in the past (one variety of which had a thin conductive wetting agent meant to improve contact conduction).
But I never use it on electronics either. For electronics I want a cleaner or cleaner with lube, for different uses. With lube should be a lube like silicone or something that doesn't thicken over the years. WD40 definitely thickens over time. On the other hand, some mfgrs purposely use thick "lube" to make pots seem more "substantial". For instance many Tapco mixers have immobilized pots after a decade of non-use, but clean up to work fine. What you really don't want IMHO is anything like a penetrating oil, which is purposely designed to apply thin and capillary into tight spaces, then turn into thicker grease.
I clean with carbon tetra cloride or carbon tri chloride. I like the Caig products (pretty large line of conductive and non-conductive cleaners, lubes, and preservatives) and used Cramolin I think it was called in the past (one variety of which had a thin conductive wetting agent meant to improve contact conduction).
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