• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Transistor Isolation

G

Gouda4U

New Member
I opened up my NAD 7175pe to replace a broken headphone jack. While the pcb was detached from the heat sink I cleaned off the old thermal paste. Some of the transistors had mica pads and others did not. Should I just replace the paste and not worry about the non isolated transistors? Thanks for any advice you send my way!
 
Register to hide this ad
Just a quick look at the schematic... I don't see any transistors that do not need to be isolated from ground. Which Q numbers are you looking at without isolation?
 
From PM "I guess you are asking for the part numbers of the non isolated transistors? That would be D1706 (x2) B1155 (x2) and a very small one C1953R (x2). I have no technical knowledge but can solder. That's how I got myself in this mess!"
Click to expand...

Really should keep this in the forum rather than PM. That way you are more likely to get the most help.
I was actually looking for the parts designators to help me find them on the schematic. Looks like Q707, Q703, and Q609 (and their matching parts in the other channel).

Datasheet for the 2SD1706 and the 2SB1155 indicate they are in the "(TOP-3) Full Pack Package for simplified mounting on a heat sink with one screw".
The 2SC1953R datasheet indicates it is in a "TO-126B package which requires no insulation plate for installation to the heat sink".

So I would say that these parts do not require an additional insulator between the part and the heat sink.
 
Regarding the isolated transistors, CHECK WITH YOUR METER AFTER INSTALLED, THAT YOU DON'T HAVE CONTINUITY BETWEEN THE TRANSISTOR LEADS AND THE HEAT-SINK. Many times the insulation washer is damaged or missing, and even with the insulator mica or pad you still have continuity between the transistor and chassis.

transistors with insulated plastic body (no exposed metal back) don't need any extra insulation.
 
You must log in or register to reply here.
Back
Top Bottom