Quote from: J M Fahey on September 05, 2024, 04:31:07 PMthese Tech 21 guys are _secretive_

When the best name they can come up for a guitar amp is "Trademark", that company is run by IP lawyers. 

A simple-minded rock and roll or metal guy would only think of "Destroyer", "Striker", "Invader", "Ball Wrecker" and such, not "Trademark".

Quote from: phatt on August 17, 2024, 08:42:49 AMI lost my Wife last year And 20 years earlier she lost her son to suicide, she carried on but it left a mark on her outlook on life.
Yes the things that life throws at us can be soul destroying.
So I have some understanding of your great loss.
Phil.

Ouch!
Hard blows for sure but hey, we must keep playing no matter what cards does Life deal us.
What else? 🤷🏻

In the real world, no big deal.
Since forever I used 100k to ground at the input differential leg and 10k as NFB from speaker out to negative keg and my typical offset is around 40-50 mV so I never bothered to correct it.
So you are fine.

Intrigued by this post, searched Heaven and Earth for a Trademark 112 schematic or at least a Power engine 60-112 which seems to be the same cabinet, power amp, power supply, only lacking the multi-emulation multi-effect preamp and sporting only a basic tone control since it's meant to be driven from some multi-effects pedalboard.

Could NOT find anything, these Tech 21 guys are _secretive_ , but one of their designers complained about Yamaha copying their product.

They even use same Celestion 70-80 speaker!

And *that* service manual is available at Elektrotanya. 😉

Different power amp technology (discrete vs chipamp) but the useful point is that power amps have no fancy tricks at all,they are flat and clean (why doesn't that surprise me?), 20X gain (so about 700-1000 mV sensitivity), only slight mod is mixed feedback technology which functionally "changes nothing"

So what's my point?
Now I am *quite* certain your amp literally uses "official datasheet" schematic, so you can use that as a Service Manual.
Not "flying blind" any more. 😊

Hey! KILLER amps and designs, very original, very good looks.
"They sell all by themselves"
I would be a present from the Gods for anybody to be able to get his hands on this and start a new Company or endeavour with so much "start up" job already done for him.
It would save YEARS. And money and teething troubles.
Guess you would also transfer your current customer database, to which they would later add on.
This is similar to buying a working Company, ready to keep earning money  "tomorrow".
Hope some smart guy jumps in to profit from all the groundwork you already did.

 
 

Also with power on gently pressing on the board in different places
(with an insulated probe) can help track down an offending component.
Phil.

Quote from: phatt on September 03, 2024, 08:41:45 PMAhh yes nothing worse than intermittent crackles.
Yes a component dying or a cracked or cold solder joint,, my guess you have a cracked track hiding in the maze.
Get yourself a wooden skewer stick and while amp is on gently poke and move components on the PCB. you can get lucky and find the part that is causing the drama. The bottom side will not be easy to access so disconnect an pull the board out then with a magnifying glass in bright sunlight go looking for hair line cracks, especially around the solder pads.

I actually own a SS Laney amp, even earlier model that yours and it developed a crackle last year which drove me mad but finally found a hairline crack which was actually hidden by a solder lump so Even with magnification you could not see it.
Keep us posted, Phil.

Thanks for the response and suggestion. I'll start poking it with a stick (!) and see what happens.

I bought a much later LC15 when this one went wrong and that's popping and crackling too. I owned several minis when they leaked or died in wet weather. I'm clearly a sucker for brand loyalty to brands whose products are a bit.....interesting!

I'll start a new thread, but any chance anyone has the schematic for the mpa-25? I have one of them as well.

Ahh yes nothing worse than intermittent crackles.
Yes a component dying or a cracked or cold solder joint,, my guess you have a cracked track hiding in the maze.
Get yourself a wooden skewer stick and while amp is on gently poke and move components on the PCB. you can get lucky and find the part that is causing the drama. The bottom side will not be easy to access so disconnect an pull the board out then with a magnifying glass in bright sunlight go looking for hair line cracks, especially around the solder pads.

I actually own a SS Laney amp, even earlier model that yours and it developed a crackle last year which drove me mad but finally found a hairline crack which was actually hidden by a solder lump so Even with magnification you could not see it.
Keep us posted, Phil.

Hello,

I'm Ian from Surrey. I've acquired several amplifiers over the last 30 years and nearly every one has a problem of some sort. I live in a damp old cottage and wonder whether that has anything to do with or if they just give up after a short period of having to amplify my torrid guitar playing!

My electronics skillset is limited to building and soldering circuitry (I've made a lot of pedals) with only a rudimentary understanding of how the circuit actually works. I can solder, have basic test equipment (multimeter, signal generator, etc) and know how to follow a schematic.

The first amp I'm trying to tackle is a 1994 Laney GC50 that I bought new. A few years ago, it developed an annoying crackle (like someone screwing up newspaper - crackle, gap, crackle, gap, long crackle, short gap, etc)) that made me sideline the amp and buy another amp. I'd like to get the Laney up and running again as it takes up a lot of space for something that's currently useless!

There are two boards - the combined power supply and power amp board and the preamp board. If I disconnect the ribbon cable between the PSU/power amp board and the preamp board, the problem persists and I can still play a guitar through the Effects Receive jack so it's clear that problem exists somewhere in the PSU/power amp board. This board has lots of hole-through big components on its upperside and as many surface mount devices below.

So far I have:
1. Cleaned the contacts on all the jacks (speaker, headphone, DI out, Effects send and return)
2. Tested with a cable between the send and return jacks
3. Replaced the two 2200uF PSU electrolytics (a cheap and simple fix if it worked - it didn't!)
4. Replaced all the upper side (hole through) capacitors, both polyester and electrolytic (ditto on the cheapness and ease....and the not working bit)

And the crackle is still there!

But there are still 50% of the components to replace and my policy of blindly replacing stuff until I eliminate the issue was fine for cheap capacitors but BD909s are £4/$5 each. So I'd appreciate some help with a more nuanced approach!

I've attached a photo of the board and the schematics associated with it. Note this board is part number 9074 but the schematic for that board shows TIP35 power transistors. My amp has BD909 transistors and a pair of 2200uF power supply capacitors, but everything else on the 9074 diagram seems to be the same. There's a rectifier module they don't give a part number for but it's a KBL403.

Thanks for any help you can give.

Ian