[HELP] Repair Arcam Alpha 2 - 240v

CrustyD3mon

Member
2012-01-05 3:16 pm
Hey guys,
Just bought an Arcam Alpha 2 for some bucks that don't turn on..
When i open it i saw that somebody already solder some resistaces and chage the fuses for ones with wrong values...so they blowup...

I saw that resistances burned too...and i want to replace them all for resistances with the right values and right fuses too...

Can anyone help me getting the values of the burned materials? Anyone have schematics for this or something?

[IMGHTTPSDEAD]https://dl.dropbox.com/u/21378485/2013-01-25%2021.34.37.jpg[/IMGHTTPSDEAD]

[IMGHTTPSDEAD]https://dl.dropbox.com/u/21378485/2013-01-25%2021.35.33.jpg[/IMGHTTPSDEAD]

[IMGHTTPSDEAD]https://dl.dropbox.com/u/21378485/2013-01-26%2002.22.48.jpg[/IMGHTTPSDEAD]
 
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The damage suggests the amplifiers output was shorted for a time. One of the output transistors (Q114) has failed and been replaced. Really, both should be replaced.

If you find the transistors FST239/240 are damaged, they became obsolete and Arcam used Zetex ZTX653/753 as replacements.
 

CrustyD3mon

Member
2012-01-05 3:16 pm
The damage suggests the amplifiers output was shorted for a time. One of the output transistors (Q114) has failed and been replaced. Really, both should be replaced.

If you find the transistors FST239/240 are damaged, they became obsolete and Arcam used Zetex ZTX653/753 as replacements.

Ok...nice tips....i will need because i have some "electronic limitations" ;)

The output transistors i need to check them...both fuses are blown and i don't check any of them yet...
Another thing...what is RV1 and RV101 ? i think one of them are burnet too....
 

KatieandDad

Member
2011-11-17 3:49 pm
UK
Looking at the schematics, something pretty horrible has happened to fry RV1 and RV101. Still do not be disheartened, it can be repaired.

My first move would be to remove all the obviously burnt components. Then test each of the remaining semiconductors.

Due to the age of the amplifier change all the electrolytics as a matter of course.

Any lifted PCB tracks should be cut out unless you are adept at PCB repair. Photograph the artwork before you start so that you can see what you started with.

Any blackened PCB material needs to be removed too as it will have carbonised and will have become conductive.

Next job it to rebuild the PCB itself. Tissue and Araldite in thin layers is an excellent way of repairing PCBs damaged in this way. Bit like Dope and Tissue used in RC aeroplanes.

Drill the missing holes.

Replace the components and then use P to P insulated wiring to replace the missing tracks.

Do be aware that the damage may be more extensive than you originally think. It may not work after initial repair action has been taken.
 

CrustyD3mon

Member
2012-01-05 3:16 pm
Woww...ok...first thing first....so i will remove every aparently burned component from the board...

regarding the sections burned on the PCB...the ones that are only burned superficially i only need to use a small drill to remove the "black" right ? or need to cutoff a big hole with the entire section? :S

I will buy the following material:
Araldite:
Araldite AB Epoxy Adhesive Glue 5 Minutes Rapid New | eBay
PCB glue for cover the repaired circuits:
100g PCB UV Curable Solder Mask Repairing Paint Blue Negative Photoresist | eBay
And silver condutive glue to repair ( what do you think about this paste?)
0 2ml New Silver Conductive Wire Glue Paste for Electronics Repair Applications | eBay

regarding the "Tissue" to use with araldite....what kind of tissue is that and where can i find some of it?

Thanks for the guide
 

KatieandDad

Member
2011-11-17 3:49 pm
UK
Repairing the PCB you don't need to drill "ruddy great holes" just remove the carbonised bits. Bit like a dentist just dremmel out the black bits.

DON'T use conductive paint its useless. Once you've got back to solid track P to P with wire.

Tissue is tissue. If you want to go posh you can buy it from RC shop but good old toilet tissue or kitchen roll will do. Kitchen roll is probably that little bit stronger.

Also no need for the solder mask repairing paint.
 
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CrustyD3mon

Member
2012-01-05 3:16 pm
Repairing the PCB you don't need to drill "ruddy great holes" just remove the carbonised bits. Bit like a dentist just dremmel out the black bits.

DON'T use conductive paint its useless. Once you've got back to solid track P to P with wire.

Tissue is tissue. If you want to go posh you can buy it from RC shop but good old toilet tissue or kitchen roll will do. Kitchen roll is probably that little bit stronger.

Ok when i clean the carbonized parts i post a pic before apply araldite ...and you can give me a advice if its ok or not.....:D:D
 

CrustyD3mon

Member
2012-01-05 3:16 pm
All the Araldite and tissue will be doing is rebuilding the "plastic" of the PCB.

In days gone by PCBs were made of layers of Resin and Fibre.

This one it's a kind of fiber too...in the place that seems worst...i remove already the three burned resistances...and seems to be a kind of fiber:

[IMGHTTPSDEAD]https://dl.dropbox.com/u/21378485/2013-01-28%2019.10.05.jpg[/IMGHTTPSDEAD]
 
You should also check Q8, MPSA056 and R27 (56R), and Q7 FSWT239 and R30. If theese are blown, and as Jaycee says, the FST239/FST240. (Q11 and Q12)
Ah, My component-references are to the AII-schematics. I will have to look a little closer on Your pics.

Seems as if you only should add 100 in fromt of the references I wrote here.
Especially Q107 looks suspicious on the pic over here. But thees E-line transistors often look as if they have been overheated all the time.
Q110 (BC557) and the two 1N4148 diodes should be checked too. Seen similar fault in TANDBERG-amplifiersfrom time to time.
Q108 is the one near TP18, isn't it? Looks pretty worn that one too.

I guess R125 just is removed for the repair of the PCB? Should not be burnt that one (47K)

By the way, R28 in the first pic also seems to have been too hot.
Similar faults there too?
 
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Yeah, Arcam used fibreglass PCB's... rather than the paper based board that is so common now.

The RV1/RV101 preset pots are for adjusting the bias current. As you can see it is a 1K linear preset. As long as you can get one that will fit the pin spacing, there's no need to get the exact brand.

As for the damage, I have seen this before on many amps. One output device failed short, so there was full voltage on the output. The IV limiter circuitry sees this as an overload and attempts to limit the current by clamping down the base of the driver transistor. Of course, this has no effect because the output device shorted, so the resistors, transistors and diodes in the IV limiter circuit also burn.
 

CrustyD3mon

Member
2012-01-05 3:16 pm
You should also check Q8, MPSA056 and R27 (56R), and Q7 FSWT239 and R30. If theese are blown, and as Jaycee says, the FST239/FST240. (Q11 and Q12)
Ah, My component-references are to the AII-schematics. I will have to look a little closer on Your pics.

Seems as if you only should add 100 in fromt of the references I wrote here.
Especially Q107 looks suspicious on the pic over here. But thees E-line transistors often look as if they have been overheated all the time.
Q110 (BC557) and the two 1N4148 diodes should be checked too. Seen similar fault in TANDBERG-amplifiersfrom time to time.
Q108 is the one near TP18, isn't it? Looks pretty worn that one too.

I guess R125 just is removed for the repair of the PCB? Should not be burnt that one (47K)

By the way, R28 in the first pic also seems to have been too hot.
Similar faults there too?

Yes...Q108 is near TP18 looks worn on the photo but i think it's not that worn...i will check anyway....

And you're right i remove R125 to clean the PCB bettter there...i have some of it in spare...so i will put a new one as soon as i get the board repaired...

The R28 it's burned too...i already measure with multimeter and it's not ok....I think both outputs circuits have the same damages...but the right one it's worst than the left.

Yeah, Arcam used fibreglass PCB's... rather than the paper based board that is so common now.

The RV1/RV101 preset pots are for adjusting the bias current. As you can see it is a 1K linear preset. As long as you can get one that will fit the pin spacing, there's no need to get the exact brand.

As for the damage, I have seen this before on many amps. One output device failed short, so there was full voltage on the output. The IV limiter circuitry sees this as an overload and attempts to limit the current by clamping down the base of the driver transistor. Of course, this has no effect because the output device shorted, so the resistors, transistors and diodes in the IV limiter circuit also burn.

Do you know what's the brand of this ones (RV1/RV101) ? i will try to check if it's easy to find the same here in Portugal...

What do you guys think about TIP3055 and TIP2955, probably any damage or not?

Today i will start removing the components and clean the board...yesterday i really have no time to start this repair....keep you guys updated and thanks to all for the tips... :)
 
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Do you know what's the brand of this ones (RV1/RV101) ? i will try to check if it's easy to find the same here in Portugal...

What do you guys think about TIP3055 and TIP2955, probably any damage or not?

The brand I have seen used is Iskra.

I would replace the output transistors anyway as a precaution, even if they test OK. They have certainly been abused and could have shortened life as a result.
 

CrustyD3mon

Member
2012-01-05 3:16 pm
The brand I have seen used is Iskra.

I would replace the output transistors anyway as a precaution, even if they test OK. They have certainly been abused and could have shortened life as a result.

Ok...but there's any problem turn on the system (After repair burned components) with this ones? i mean....if they test ok but have some damage anyway...there's any risk to burn other components again beause of this?
 

KatieandDad

Member
2011-11-17 3:49 pm
UK
As I said earlier on, unless you catch all the damaged components there is a possibility that you may blow it again before you finally repair it.

TIP3055 and TIP2955 are pretty cheap and readily available. At least no-one has tried to fake them so you can buy them on E-Bay with confidence.

You can also use MJ(E)3055 and MJ(E)2955 just make sure you get the plastic ones and not the T03 type.

I would expect that if the outputs test OK they are probably OK. Their SOAR is such that the fuses would have blown before any real significant damage was done. HOWEVER, I might be wrong, stranger things have happened.

The Power Amp is pretty simple, if you remove all the active devices for testing and replace all the electrolytics, most of the passives can be tested without removing them with the actives out of the board. Any non-electrolytic caps should be OK unless they look heat damaged.

Just BEWARE of CARBONISATION of the PCB. This must be CUT OUT and repaired otherwise you will have invisible shorts.
 
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