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Old 30th January 2013, 04:00 PM   #11
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Originally Posted by KatieandDad View Post
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.....
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Old 30th January 2013, 04:02 PM   #12
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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.
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Old 30th January 2013, 04:31 PM   #13
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Originally Posted by KatieandDad View Post
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:

Click the image to open in full size.
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Old 30th January 2013, 05:13 PM   #14
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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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Sooner or later you end up with TANDBERG

Last edited by TANDBERGEREN; 30th January 2013 at 05:26 PM.
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Old 30th January 2013, 05:17 PM   #15
jaycee is offline jaycee  United Kingdom
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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.
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Old 31st January 2013, 08:09 AM   #16
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Originally Posted by TANDBERGEREN View Post
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.

Quote:
Originally Posted by jaycee View Post
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...

Last edited by CrustyD3mon; 31st January 2013 at 08:11 AM.
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Old 31st January 2013, 11:11 AM   #17
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You can repair the board with the Araldite and tissue as already described. If you want to be clever you can use fibre glass and resin from a car body shop.
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Old 31st January 2013, 01:14 PM   #18
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Quote:
Originally Posted by CrustyD3mon View Post
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.
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Old 31st January 2013, 01:31 PM   #19
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Originally Posted by jaycee View Post
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?
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Old 31st January 2013, 02:51 PM   #20
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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.

Last edited by KatieandDad; 31st January 2013 at 03:00 PM.
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