RD AUDIO D9

mike49504

Member
2006-09-22 8:32 am
Im repairing this amp it has blown outputs and a blown power supply.

When i removed the spring clamps I noticed there are 2 differnt outputs in this amp. They are FDA24N40F and FQA28N15.

Does anyone know if this amp uses both thoose outputs or does it just use The FDA24N40D'S
 

mike49504

Member
2006-09-22 8:32 am
some kinda do some dont. I know 1 of the part numbers doesnt belong .

On 1 side of the amp i have 6 FQA28n15's that the solder is not orginal on them and 2 FDA20n40f's

On the other side of the amp i have 4 28n15's and 4 20n40f's
 
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mike49504

Member
2006-09-22 8:32 am
Ok the FDA20N40F's are the orginal outputs the solder on them is orginal The FQA28N15'S have been put in at some point and the solder job is bad .

So i have to order all new power supply fets,new outputs,new driver ic's new gate resistors, New drivers for the power supply fets.

Is there anything else i should check for that goes bad when this type of work is done on and amp (wrong outputs)
 

spooney

Member
2006-12-01 4:41 am
Yeah I really prefer the kapton tape. Only thing about it is that it is very thin and if there are any small burrs or small pieces of debris on the heatsink or transitors it can poke right through that tape when you clamp the transistors down. The mica is a real pain to work with but It seems like I've seen Perry say they are better at transferring heat than the kapton.
 
Mica insulators and the Kapton MT film are both very good. Mica varies quite a bit in thickness so it's difficult to say, definitively, which is best at transferring heat.

The mica and Kapton are suitable replacements but it's ABSOLUTELY imperative that you check EVERY transistor to confirm that the clamp is applying sufficient pressure to make it lay absolutely flat against the heatsink. The holes in the boards typically allow the transistor to be soldered in at a very slight angle. Since the leads are very rigid and the clamps relatively weak (for those using spring clamps), there is no guarantee that the clamp will be able to force the transistor to lay flat against the sink. Silicone insulators are somewhat more forgiving.

After clamping the transistors, apply additional pressure to the top of the clamp while watching the gap between the transistor/insulator/heatsink. If you can cause the heatsink compound to be displaced when pressing on the clamp, it was not laying flat against the sink. If the heatsink compound withdraws back under the transistor when you stop applying pressure, it's not laying flat against the heatsink and the clamp isn't applying enough force. This can cause the amp to fail prematurely.