Strange and Lazy repair !!!

[Jazz P Bass]

If it keeps me awake at night, I don't do it.

[bsco]

I've never seen fuses replaced with aluminum rod. I've seen plenty that were wrapped in aluminum foil (sometimes from a cigarette pack).

What about lazy repairs that WE do. C'mon!?! I know there are some shortcuts we've all taken that are less than ideal but known to be "good enough". Is anyone here willing to fess up? I'll go first...

On a few occasions where board removal was a real PITA I've replaced "through hole" PCB components by snipping the leads and soldering the new component/s to the old leads. Likewise, when making value changes on such boards I've also just piggybacked components on existing ones rather than pull the board to change the existing value. I'm not proud of this, but I don't expect it to cause any real problems either.

I have clipped resistor leads and soldered in new ones on a couple of occasions...but made sure that it would not affect anything.....However there were times where I was tempted to do this but decided to pull the board and how lucky I was....bad connections on heavy duty components such as jacks and pots...the amp would have been back next week for more repairs......so if I have to do that I will, but I try very hard not to.....sometimes you don't have much of a choice....unless you deem the unit un-repairable...or the customer can't or don't want to spend the money for the labour....which usually doesn't happen very often...

[g1]

I hate to disappoint, but this is not the case (double fuses) in SVT-2 Pro. The first fuse is for the whole amp (including power transformer) and the second is for the filament transformer only. The second fuse is 1.5A and the value on the schematic is correct.

Doh! Thanks Markus. What's with this disturbing trend of not showing transformers on schematics?
Or schematics that are just mazes of terminals & connectors, Marshall being especially bad. It wouldn't be so annoying if they included a road map of the connectors/terminals, but they never do.

[The Dude]

So what exactly happened to the IC pins themselves?

Must have laid the IC & heatsink over & snapped them.

"Here's your amp back. Fresh as a daisy."

My best "guestimate" is that the pins broke off at the board and were no longer able to reach through the holes. The wires were simply tacked on to the leads- no loops or anything substantial. I wouldn't consider it a stable solution. Many of the connections from wire to lead had come loose. You could probably make the existing IC work, but why? Labor cost to do all of the jumpering would be more than just getting a new IC and doing it right.

[The Dude]

I've never seen fuses replaced with aluminum rod. I've seen plenty that were wrapped in aluminum foil (sometimes from a cigarette pack).

What about lazy repairs that WE do. C'mon!?! I know there are some shortcuts we've all taken that are less than ideal but known to be "good enough". Is anyone here willing to fess up? I'll go first...

On a few occasions where board removal was a real PITA I've replaced "through hole" PCB components by snipping the leads and soldering the new component/s to the old leads. Likewise, when making value changes on such boards I've also just piggybacked components on existing ones rather than pull the board to change the existing value. I'm not proud of this, but I don't expect it to cause any real problems either.

On RARE occasion, we've probably all done that. When I've done it, I created a hook in both leads and crimp them together before soldering. It makes for a solid connection that's not dependent on solder alone.

[Audiotexan]

On a few occasions where board removal was a real PITA I've replaced "through hole" PCB components by snipping the leads and soldering the new component/s to the old leads.

I've done close to that...it's a quick 'cheat method' but, it bugs me if it doesn't look like "factory".

My occasional method:
On a few occasions where board removal was a real PITA I've replaced "through hole" PCB components by snipping the component leads and then removing the old lead remnants, then using chem-wik to clean the thru-hole, and then soldering the new components in where the old component was.

The only thing with this method is, you have to be extra careful not to flow too much solder so that you don't accidentally make a bridge on the bottom, otherwise you end up having to pull the whole damn board anyways, negating the 'cheat' in the first place. lol

[52 Bill]

The problem that I've seen with soldering in components to the cut off leads of the old parts is that the solder joint on the underside of the board reheats and will become a cold joint if you are not careful.

The worst thing I can remember doing is drilling a hole through the chassis of a cheap Gorilla practice amp to resolder a loose input jack. To get the board out you had to remove the power transformer as well as the heatsink, the knobs, the controls, etc.

[bsco]

The problem that I've seen with soldering in components to the cut off leads of the old parts is that the solder joint on the underside of the board reheats and will become a cold joint if you are not careful.

The worst thing I can remember doing is drilling a hole through the chassis of a cheap Gorilla practice amp to resolder a loose input jack. To get the board out you had to remove the power transformer as well as the heatsink, the knobs, the controls, etc.

I had few amps like that.....Never thought of doing that.....I went ahead and had to remove everything in order to get the board out....PITA....

[jbmdisco]

I should rename this thread 'Strange, Lazy and Russian roulette'
I have just bought a 40year old Sound City 120 guitar amp. It was cheap, in good cosmetic condition and came with a free 4x12 matching cabinet. The previous owner admitted that he'd had it for about 20 years without as much as even cleaning let alone servicing. The only thing he told me was that for those 20 years there had always been a strange crackle but putting it down to a 'feature' rather than a problem.
Having stripped the amp from the case and giving it a good clean I noticed that one of the power caps has some insulating tape around the bottom. I powered the amp up and sure enough a crackle and buzz. I metered between the top of the 'taped' cap and the chassis to find a 'healthy' 121 vdc flowing like a river. Out of intrest I plugged a guitar into the input and metered between the strings and this cap - 121vdc.
I contacted the previous owner to find out if anyone had at all looked at the amp during his ownership, just to check if maybe he'd forgotten. But no. So for 20 years this guy was a microphone away from a good frying.
I suggested he give me 6 numbers for the lottery !!!
Anyway, remaining with this sound city amp, the caps in question are 200uF @ 350vdc. I have looked around for replacements without success. Can anyone recommend suitable value replacements ?

[MarkusBass]

I'm afraid that there is nothing wrong with the cap. If you look at the schematic: http://soundcitysite.com/sc_120_2.jpg , you'll see that there are two capacitors in the power supply, one stacked on top of the other. It's due to the fact that the power supply voltage of the power amp is higher that the voltage allowed for the cap. That's why there is isolation tape on the cap. Problems with the amp are caused by something else - you may create a new thread for this amp.

Mark

[km6xz]

The reason the module was not wired the same is because it was not the original, which has been out of production for years. There are newer modules available with higher power but they are not plug-in compatible and one pin difference in count, different mounting screw spacing etc. Be wary of modules on eBay unless you know the supplier because a lot of those from China are remarked as higher power versions or just are not original.

[g1]

I'm afraid that there is nothing wrong with the cap. If you look at the schematic: http://soundcitysite.com/sc_120_2.jpg , you'll see that there are two capacitors in the power supply, one stacked on top of the other. It's due to the fact that the power supply voltage of the power amp is higher that the voltage allowed for the cap. That's why there is isolation tape on the cap. Problems with the amp are caused by something else - you may create a new thread for this amp.

Mark

Yes, perhaps the crackle and pop is due to breakdown of insulation provided by the electrical tape. 220uF is a more common value you will find (instead of 200uF).

The reason the module was not wired the same is because it was not the original, which has been out of production for years. There are newer modules available with higher power but they are not plug-in compatible and one pin difference in count, different mounting screw spacing etc. Be wary of modules on eBay unless you know the supplier because a lot of those from China are remarked as higher power versions or just are not original.

Not sure if this was meant to go in some other thread?

[MarkusBass]

Not sure if this was meant to go in some other thread?

I think it was an answer to questions about the STK404-130S module. This is called multi-threading .

Mark

[rf7]

I think I've seen that guys handiwork in a Marshall too. I just gutted his circuit.