Quick diagnosis?

[squire5]

I was using my Laney RBG400 at home this morning.It started to crackle slightly,and then emitted a loud hum which is uncontrollable.I know its a long shot but can any boffins out there give me any pointers as to what it could be,and more importantly,is it worth fixing?The amp is old and has seen better days.Thanx.

[DGBass]

A loud uncontrollable hum on the speaker output usually means something has gone on the output section of the amp, test for dc on the output that shouldn't be there. But not always! Laney amps of this era are fairly simple to repair and parts can be found for them easily online. If an output transistor had failed, it would usually take out the fuse as well, so it may be a failed smoothing capacitor or even a dry solder joint on one of the caps. Vibration over a long period can rattle things loose and from Laney RB bass amps I've worked on before, they seem to be sparing on the hot glue to keep big caps fixed and stable on the circuit board.  The pic below is from a bigger 300w RB version of your combo that had similar issues. The big black bits with 5/22 on them are the smoothing caps. If they move or feel wobbly at all it could be they've worked loose. Any good amp tech would find an issue like that very quickly. Can be diy but as with anything electrical with dangerous voltages present, you have to be careful and not get yourself electroplated. If in any doubt, an amp tech is the way to go. Any amp is worth repairing if its cheaper than buying something to replace it. 🙂

 

 

 

 

Edited August 29, 2023 by DGBass
smoothing out ripples

[Bill Fitzmaurice]

Hum could be power amp sourced, but not necessarily. A bad connection somewhere in the amp could be the cause, as could a blown component in the power supply. DC doesn't cause hum, because DC doesn't make any sound. Loud hum indicates AC that shouldn't be there, as in the case of a bad power supply.

[squire5]

Thanks for the really helpful input guys.The amp has been sitting in the one spot in my bedroom for months now and only gets used as a 'home noodling' amp,ie doesn't get moved about at all.Its ironic as I'm awaiting delivery of a new Harley Benton 5 string MM style bass tomorrow and now I've no amp.Well I've got a Fender Rumble 15 which is better than nothing,almost.My usual rig is a Trace Elliot 4 x 10 plus 250 watt amp so thats not getting in my bedroom.I'm in the UK (N.Ireland) and amp techs are thin on the ground over here.But I'll keep looking.Cheers.

Edited August 22, 2023 by squire5

[BassmanPaul]

If you want the amp repaired take the thing to a proper tech for service. Anything you try o do to fix the amp will likely make matters worse and more expensive to remedy.

[squire5]

Thank you for your insightful and helpful reply Paul, but if you had read my post you would see that 'proper techs' are thin on the ground,hence my original post.

[BassmanPaul]

My advice stays the same. If you want the unit repaired properly it needs to go to a tech. You'll just have to find one somewhere near your area. In my time I have repaired hundreds of amplifiers. The most difficult repairs have been those whose owners have tried to fix themselves. Undoing the mess that those owners left behind were a nightmare!

 

 

Edited August 22, 2023 by BassmanPaul

[BassmanPaul]

You could try contacting the manufacturer. Possibly they may be able to direct you to an authorized tech familiar with your amplifier.

 

LANEY AMPLIFICATION

STEEL PARK ROAD

COOMBSWOOD BUSINESS PARK

HALESOWEN, WEST MIDLANDS

B62 8HD, UK

+44 121 508 6666

[Baloney Balderdash]

Could be something as simple as the pots needing a cleaning.

 

Any additional crackle when any of the pots are turned?

 

If so a fix could turn out to be as quick and easy as to spraying some electronic cleaner inside them and giving them a series of wiggles back and forth.

 

Edited August 25, 2023 by Baloney Balderdash

[squire5]

Not really BB.The hum is not affected by the volume control ie it stays the same volume no matter what you do.Having said that I extricated the amp itself from the cab expecting to see maybe a burnt cap or something but no.Everything looks fine.In fact theres precious little to the amp.A small board about 15 x5cms,a large torroidal transformer and another board for the controls.The caps look fine not bulging or burnt.I may have found a tech about 30 miles from me.I'll see what he thinks.Cheers.

[agedhorse]

19 hours ago, Baloney Balderdash said:

Could be something as simple as the pots needing a cleaning.

 

Any additional crackle when any of the pots are turned?

 

If so a fix could turn out to be as quick and easy as to spraying some electronic cleaner inside them and giving them a series of wiggles back and forth.

 

This is a quick way to ruin a set of otherwise good pots. Cleaning pots requires only the tiniest spray inside AND the only product I have tested that didn’t create longer term problems is Caig DeOxit D5. There may be something similar in Europe, but the majority caused damage to the test pits over time.

[agedhorse]

On 22/08/2023 at 06:57, DGBass said:

A loud hum on the speaker output usually means something has gone on the output section of the amp, its usually an indication of a dc signal which shouldn't be there. But not always! Laney amps of this era are fairly simple to repair and parts can be found for them easily online. If an output transistor had failed, it would usually take out the fuse as well, so it may be a failed coupling capacitor or even a dry solder joint on one of the caps. Vibration over a long period can rattle things loose and from Laney bass amps I've worked on before, they seem to be sparing on the hot glue to keep big caps fixed and stable on the circuit board.  The pic below is from a bigger 300w version of your combo that had similar issues. The big black bits with 5/22 on them are the coupling caps. If they move or feel wobbly at all it could be they've worked loose. Any good amp tech would find an issue like that very quickly. Can be diy but as with anything electrical with dangerous voltages present, you have to be careful and not get yourself electroplated. If in any doubt, an amp tech is the way to go. Any amp is worth repairing if its cheaper than buying something to replace it. 🙂

 

 

 

 

Since it’s a direct coupled output topology, those caps can’t possibly be coupling caps. Therefore, the rest of the information provided is suspect.

[Baloney Balderdash]

41 minutes ago, agedhorse said:

This is a quick way to ruin a set of otherwise good pots. Cleaning pots requires only the tiniest spray inside AND the only product I have tested that didn’t create longer term problems is Caig DeOxit D5. There may be something similar in Europe, but the majority caused damage to the test pits over time.

Well, worked for me.

 

And the pots I sprayed were really bad, but now works flawlessly and have done so for years since I sprayed them.

 

I fail to remember the name of the product though, but it was made specifically to clean circuit boards. 

 

Edited August 26, 2023 by Baloney Balderdash

[itu]

There seems to be an FX loop there. Have you tried a cable from send to return?

(One of the most common issues with any amp: oxidized comtacts.)

[Phil Starr]

It's pretty much impossible to be certain but I'd certainly be having a quick look at the capacitors in the power supply before even tuning the amp on if I opened her up. Those two big caps are smoothing capacitors. Electrolytic capacitors often do degrade over time.

 

It's not really a diy job for a beginner. You at least need to be able to use a multimeter and a soldering iron to locate and replace components and there are serious risks to you working on a power supply inside an amp like this. DC shocks from the power supply are much more formidable than ac shocks from the mains and neither are to be recommended. Big capacitors can store significant charge for hours even after the amp is turned off so you are at significant risk of a shock that might at the extreme end result in death. I'm reluctant to say anything is beyond a skilled DIY'er but poking around inside a bass amp is not the ideal place to start the learning process. 

 

Having said that these amps are easy to work on and shouldn't be fearsomely expensive to repair. HNAudio and rocknrollworkshop are in Newtownards and Belfast respectively a quick google search reveals. Get a quote/estimate and make a decision.

Edited August 26, 2023 by Phil Starr

[Phil Starr]

[Chienmortbb]

2 hours ago, Phil Starr said:

Those two big caps are smoothing capacitors. Electrolytic capacitors often do degrade over time.

It’s true that electrolytic caps can degrade but that is unlikely to be the cause if the failure happened suddenly. Also sudden failure of electrolytic capacitors is often visual in that they will either deposit electrolyte close by or bulge/explode.

 

4 hours ago, agedhorse said:

Caig DeOxit D5. There may be something similar in Europe, but the majority caused damage to the test pits over time.

De-L it is available in Europe but it is very expensive. In my experience, as pots age and are used, two things happen. Firstly, parts of the track flake off causing debris that disturbs the wiper causing crackles and noise. There is also a chance that dust from the outside world gets into the pot and similarly disturbs the wiper and makes the pot crackle. As De-Oxit is specifically designed for cleaning and lubricating pots , I am sure it is better than switch/contact cleaners. WD 40 should not be used anywhere in an amplifier.

 

Another issue with pots is that a result of the track material flaking off, the track wears out. This is the only way I can see that a pot could cause hum, where a pot becomes open circuit. 

As for a DIYer trying to fault find, it is best to leave it to the professionals, they have the knowledge and equipment to fault find.  Laney’s service department are helpful and I would consider ringing them as it may be quicker and cheaper in the long run to send it to them.

[DGBass]

5 hours ago, agedhorse said:

Since it’s a direct coupled output topology, those caps can’t possibly be coupling caps. Therefore, the rest of the information provided is suspect.

Thaks for the clarity @agedhorse. Smoothing caps would be correct as Phil Star kindly pointed out. I wouldn't agree entirely with your sweeping logic, I did point out as with anything electrical with dangerous voltages present, you have to be careful and if in any doubt an amp tech would be the way to go. I wouldn't say safety advice or a suggestion to take it to a tech if you have any doubt about what to do was suspect information. Forum diagnostics are never going to be a perfect way to help another member fix a broken amp, it was only my experience of Laney RB designs I was trying to convey.  I'm sure we all only try to share our experiences with best intentions and maybe if enough people do, especially the more learned forum users with vast knowledge and experience of musical equipment and i'm not reffering to myself as I'm a DIY-er,  another potential diy-er might gain an insight into the innner workings of their equipment from collective viewpoints, take that first step to realise that it may be possible with an appreciation of electrical safety, some thought, and bit of learning to save a broken amp from the dumspter.  And of course save £££'s in repair bills.

[agedhorse]

I see the results of DIY repairs regularly, generally the first thing that comes to mind is "what were they thinking?", followed by "why?" followed by "what the hell?".

 

You talk about saving money, but in reality most of the time when an amp (I only service Genz Benz, Genzler and Mesa) comes into the shop without somebody monkeying with it, the amp falls into the $100-$125 (USD) flat rate repair cost. When repair attempts are made that result in additional work and clean-up of the mess (most of them), it automatically doubles the cost of the repair because now EVERYTHING is suspect and a lot of additional disassembly, inspection and follow-up needs to be done in order to fully warranty the repair.

 

I immediately recognized that you are a DIY enthusiast. Gaining appreciation for the inner workings of an amp starts with education and learning before attempting to repair something that they are unfamiliar with. The DIY "industry" is full of folks who claim to know more than the (real) experts, talk up a good game, yet anyone who really understands electronics can see through the crap pretty quickly. It's just how it is.

 

Now the Laney amp in question uses a unique Sanken STD series output device that's been out of production for quite some time. It's unique not just because it's a Darlington device, but because there's a bias offset and thermal compensation diode built right onto the die and is an integral part of making a Darlington output device work well in a linear output circuit. This is something that an experienced and qualified service tech should know, but VERY uncommon in general. Seeing the date written on the filter caps suggests that somebody has already been into the amp and did a "cap job" (so rarely do caps less than 40 years old actually fail that this is immediately suspect as the root cause of damage) that may be causing or contributing to the symptoms. The bigger question an experienced tech would ask is "what else has been messed with, and what other damage may have been caused?" This is why there is no way to diagnose this amp over the internet, no matter how good the intentions might be.

 

Also, the majority of these parts being sold over the internet (eBay, Ali Express, etc.) are fakes, counterfeit knock-offs. OnSemi made a similar part (not a Darlington, nor is it pin for pin compatible) which is also essentially out of production. 

[agedhorse]

6 hours ago, Chienmortbb said:

It’s true that electrolytic caps can degrade but that is unlikely to be the cause if the failure happened suddenly. Also sudden failure of electrolytic capacitors is often visual in that they will either deposit electrolyte close by or bulge/explode.

 

De-L it is available in Europe but it is very expensive. In my experience, as pots age and are used, two things happen. Firstly, parts of the track flake off causing debris that disturbs the wiper causing crackles and noise. There is also a chance that dust from the outside world gets into the pot and similarly disturbs the wiper and makes the pot crackle. As De-Oxit is specifically designed for cleaning and lubricating pots , I am sure it is better than switch/contact cleaners. WD 40 should not be used anywhere in an amplifier.

 

Another issue with pots is that a result of the track material flaking off, the track wears out. This is the only way I can see that a pot could cause hum, where a pot becomes open circuit. 

As for a DIYer trying to fault find, it is best to leave it to the professionals, they have the knowledge and equipment to fault find.  Laney’s service department are helpful and I would consider ringing them as it may be quicker and cheaper in the long run to send it to them.

Correct on all accounts.

 

Fortunately, the track flaking off or delaminating from the substrate is very rare these days with any of the name brand parts, though I'm sure it can occur with knock-off pots from China and India (for example). 

 

The DeOxit D-5 used in TINY amounts is generally safe and effective (IF the problem is due to a pot, which in this case is almost 100% likely it's not). PCB cleaners contact cleaners and such are generally damaging to pots and also surrounding plastics like the housings of header connectors, switches, etc. WD-40 is just nasty and like silicone products don't belong anywhere near electronics.

[Downunderwonder]

3 hours ago, agedhorse said:

the Laney amp in question uses a unique Sanken STD series output device that's been out of production for quite some time. It's unique not just because it's a Darlington device, but because there's a bias offset and thermal compensation diode built right onto the die and is an integral part of making a Darlington output device work well in a linear output circuit. This is something that an experienced and qualified service tech should know, but VERY uncommon in general. Seeing the date written on the filter caps suggests that somebody has already been into the amp and did a "cap job"

Not sure we're still talking about OP's amp. The pic is from the helper.

[agedhorse]

53 minutes ago, Downunderwonder said:

Not sure we're still talking about OP's amp. The pic is from the helper.

I was addressing the Laney in the picture. If that’s not the OP’s amp, that’s another matter.

[BassmanPaul]

@squire5 Did you contact the manufacturer? in my mind that's the first step you should have taken. Bit late now on the weekend but you should give them a call on Monday.

Edited August 26, 2023 by BassmanPaul

[squire5]

22 minutes ago, agedhorse said:

I was addressing the Laney in the picture. If that’s not the OP’s amp, that’s another matter.

My amp is the Laney RBG400 which has a lot less inside than that pictured by DGBass.Ive managed to oontact a guy in Lisburn N.Ireland.Says he'll take a look at it.

[agedhorse]

2 hours ago, squire5 said:

My amp is the Laney RBG400 which has a lot less inside than that pictured by DGBass.Ive managed to oontact a guy in Lisburn N.Ireland.Says he'll take a look at it.

Good choice, hope yours doesn't use those output devices (may not be the output devices, but the originals are pretty much unobtanium unless Laney's service network still has service inventory available)