PLEASE HELP! Problem with Genz Benz Neo Pak 3.5

[stillplayin1975]

I'd not used my Neo Pak 3.5 for a couple of years. I've started using it again but it's started making terrible noises when i first turn it on.
When I turn the amp on it makes a high pitched squeal like noise but this stops after about 5 mins and it returns to normal. I replaced the tube with a fab Harma Cryo but i'm still getting five minutes of ear splitting shriek that no control changing will stop. It seems to be coming from the amp and not the signal path.
Any advice greatly appreciated? Many thanks, Alex[attachment=162183:IMG_2188.mov]

[Dandelion]

As its been stood maybe the jack sockets may need a bit of a clean. I have read somewhere that GB shuttles (a different beast I realise) can develop noises from dirty effect loop return sockets when they are not used for a while.

[stillplaying1965]

dear Alex

 

did ever you find a solution to the squealing problem on your GenzBenz NeoPak 3.5?

 

mine has the same problem, also after a long (Covid)standstill

it also goes into the Protect-mode

squeals seem to emerge from the power supply module, as if the switching transistors and/or the power diodes make the cooling fin resonate

 

tried cleaning and bridging the send/return and replacing the pre-amp tube, to no avail

 

I kind of worry, as GenzBenz used to look upon the power supply as non-reparable

and also GenzBenz went out of business

 

this also makes me worry about all modern amps with a switching power supply (especially the resonant types) and about the most recent "full-digital" types

what would force me to go back to the weighty classic amps

 

kind regards

Peter

Belgium

[agedhorse]

The problem has nothing to do with tubes or anything like that.

 

Generally the power supplies are not repairable because the safety certification (especially in the EU) depends on many critical factors within  the power supply itself. It's no different than trying to repair a conventional power transformer that fails... it can't be rewound without break-down voltage testing and re-certifying as the EU safety regulations view these parts as critical to safety. This is true of all SMPS (including those integrated into class D power amps, mostly designed in the EU by the way, we are not allowed to repair except for a limited number of specific faults).

 

That said, I see a failed NeoPak SMPS maybe once a year at the most, and I'm the factory service guy (the brand is still supported, but sometimes it's not economical to do so outside of N. America. Generally I can repair most defects, but some components are no longer manufactured and as of the beginning of this year I don't have any of those components left. I did have a few replacement supplies, but none are left. The amp was discontinued 18 years ago, and though I still support just about everything with the amp except the parts (specifically the power supply) that I do not have. I can support any Fender authorized service center in the EU that is willing to work on it though. 

 

They are not easy to work on however (even with the factory test fixtures), they are tricky and depend on critical timing throughout the circuit. They can also be very dangerous without a transformer isolated test bench and equipment. Most techs don't work on SMPS for these reasons.

 

Regarding the more recent amps that use the ICEPower modules, these are all still in stock (still a current part) and available to any Fender authorized service center through the Fender EU parts network. For those in N. America, there's an $85 flat rate factory service program for all of these amps. I know that doesn't help you, but those members in N. America may find this useful.

 

If you message me, I can look to see who in your area might be an option. The challenge is that the cost of repair is likely more than the amp is worth because of the amount of labor involved. If you were in the US, I certainly look at it, but even if I couldn't fix it, I would make you an offer because it still has value as a boneyard piece.

 

Edited September 17, 2021 by agedhorse

[Musicman20]

Still responding to support help on an older product - got to give you a pat on the back for that agedhorse. 

[stillplaying1965]

very much thanks, Agedhorse

 

 

I had seen your name around on talkbass fora on GenzBenz products but I had assumed - judging on your pseudoname and on the long-ago dating - that you had retired

 

nice to see that you are the factory service guy and that there is still support, althought probably not do-able from/in Belgium

 

bought my NeoPak3.5 some 6 years ago from a Brussels shop going out of business (at very discount price), where it had been lingering on the shelf for some 10 years

chose it over a SWR350X (also at discount) for being much more rock-sounding

used it some 3 years, then came Covid19 and it stayed dormant for 2 years

and now it has this squealing thing

 

I had hoped stillplayin1975 had come up with a simple solution then

 

I just finished repairing a GallienKrueger MB150E power supply

had dropped it and one of the legs of a power diode had sheared off

easy to repare - but hard to find the culpritt

although this experience learned me most of my power supply "understanding"

 

I had hoped on a comparable simple fix for the NeoPak

I am a brewing, not an electronics engineer, so I wont venture into dangerous and complex electronics

 

seeing that the power amp is classical transistorized I am thinking first at replacing the SMPS by some other PS

unless I could fix the power supply (say soldering some new TO220 transistors or diodes, not fixing the steering circuits)

or putting the thing into the mothballs and replacing by some other lightweight bass amp

although this experience has left me doubtfully about anything switching power (supplies and digital amps)

 

 

kind regards

Peter

Belgium

[agedhorse]

There's noting inherently wrong with SMPS, they just require a lot more knowledge, skill and test equipment to repair.  It's a trade-off for smaller size and weight and greater performance. Because SMPS (not unlike transformers) area  custom product, there's only so much support available when the parts are no longer available. This is one reason why we went with the more expensive ICEPower platform, they build these by the tens of thousands because they are used by other bass amp manufacturers and in other industries as well. This means that the parts are stocked by many more sources.

 

Without being able to identify what exactly is not working properly, it's hard to suggest a solution. 

[stillplaying1965]

thanks, agedhorse

 

I did not yet try, as the squealing is rather scary, to test if pre-amp out delivers signal or if power amp can be run from an external signal

 

FWIW, my observations:

 

"protect" led is lit

"signal" led flashes when plucking (hard) a plugge-in bass

all other leds are lit (or can be when pad is pushed in)

 

cooling fan is running

 

so I guess power supply is supplying some of its voltages

so I guess the problem lies with the main voltage rail

[stillplaying1965]

agedhorse

 

in your professional opinion, does the squealing tell you anything

and that it has occured in al least two cases

 

it seems to emerge from the power supply, not the power amp, as if cooling-fin is pushed into resonace

 

maybe some insight here might be usefull if I choose to contact my local guitar/amp tech

he is kind of an electronics wizzard, not sure if he is up-to-date with SMPS'

[agedhorse]

Generally it has to do with timing issues, but with the protect LED on, it sounds like either something g else, or multiple problems simultaneously.

[stillplaying1965]

OK, thanks, Agedhorse

 

i'll take it up from here

most likely it will be the "mothballs-solution" at first

maybe later I might try to salvage the power-amp and couple it to some power-supply,possibly in another housing

or, if I get really into electronics (or find someone around who is), try to fix the power-supply

 

for now I will get my Eden E300T out

chiropractor, here I come 😉

 

kind regards

Peter

Belgium