I have this amplifier that a friend dropped off and if I hook up a power supply to it, no LED light and he says there is no sound. I pulled the unit apart and found the output transistors melted on the one side along with the resistors leading up to it. If I replace these, is there anything else I should be replacing at the same time? Do I need to power the unit with the remote hooked up to get the LED to come on or should it come on with just power and ground. The transistors are K-B688 and K-D718.
When powering up for testing use a limit resistor or 5-10amp fuse on the B+. That will prevent any damage to the new components in case something else is damaged. I would check for any high temperatures on the IC's and transistors (see if any get hotter than others and how quickly) once power is applied.
As for the remote, test it both ways (with and without). I don't think amplifiers that have the optional bass remote actually need it to function.
As for the remote, test it both ways (with and without). I don't think amplifiers that have the optional bass remote actually need it to function.
-120V -8A 80W Bce Kec Transistor Sc-65 | TOSHIBA | Distributed By MCM
They should have its pair as well. Like ian33 mentioned, you have to make sure how many components you need before ordering.
They should have its pair as well. Like ian33 mentioned, you have to make sure how many components you need before ordering.
Jeanious, where are you getting my information from? I have looked these up in several ways and keep coming up with NTE 36 & NTE 37 as a matched pair. I don't doubt what you are saying, I would just like to be enlightened as to where one goes to find the correct info because I can't find anything with the original numbers on it except for Google images. Even the suppliers I called cross to these numbers. The specs seem a little higher but close.
D718- 120V 8A 80W Bce Kec Transistor Sc-65 | TOSHIBA | Distributed By MCM
B688- -120V -8A 80W Bce Kec Transistor Sc-65 | TOSHIBA | Distributed By MCM
Those are exact replacements, listed above. The NTE36 & NTE37 are different case (TO-66), while the ones you need are SC-65. Am not using any cross reference webs, I simply look at the datasheets and quickly realize their different packages/case. While some webs will give you a different case package (as they think you have a new design and can switch package style before making/manufacturing) so they give you the NTE subs, which are NOT suitable replacements at all for your amplifier.
S-Merlington just gave you some good subs, if he says he's used them before with no issues...then I believe him and I suggest using his recommended subs. Thanks Merlington for your input.
B688- -120V -8A 80W Bce Kec Transistor Sc-65 | TOSHIBA | Distributed By MCM
Those are exact replacements, listed above. The NTE36 & NTE37 are different case (TO-66), while the ones you need are SC-65. Am not using any cross reference webs, I simply look at the datasheets and quickly realize their different packages/case. While some webs will give you a different case package (as they think you have a new design and can switch package style before making/manufacturing) so they give you the NTE subs, which are NOT suitable replacements at all for your amplifier.
S-Merlington just gave you some good subs, if he says he's used them before with no issues...then I believe him and I suggest using his recommended subs. Thanks Merlington for your input.
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So I replaced the output transistors using NTC36 & 37. I could not see any physical difference and the spec sheets for both sets was relatively the same. Jeanious if you know something, it would be nice to share. I also replaced the 220 ohm resistors which got a little warm. The unit is up and running and seems to be very strong. I have limited experience with amplifier repair. Anything I should be looking for or measuring before I kick it out the door. Thanks in advance for your help.
Sorry I got them confuse for some reason, I was getting a TO3 (metal) package instead of the TO247 (TO3P).
The ones you choose seem to be better spec than the originals, good job. How much did they cost and where did you purchase them?
Check the DC offset for both channels, should be below 30mv (the lower the better).
The ones you choose seem to be better spec than the originals, good job. How much did they cost and where did you purchase them?
Check the DC offset for both channels, should be below 30mv (the lower the better).
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I got them from a company called SAYAL. They are in Cambridge, Ontario, Canada. They were $53.00(for a set of four -two PNP, two NPN) taxes in. I could have bought them from Allied Electronics as well but by the time I add shipping etc, same price or better. Our electronics stores are dwindling over here so I have to take what I can get. By DC offset, I am guessing you mean the voltage output on each channel. Like I said, a lot of this is new to me. Fumbling my way through right now so really appreciate the help. If you could shed some more light on this, I would really appreciate it. Thanks in advance
Woah I told you those NTE devices where expensive as hell. I would of never paid that much for them....espeacially when someone else (merlington) gave you replacements that where 2.00 (Mouser). Mouser is a few minutes away from me, I could of picked up a few and shipped them to you for 5.00 (total would of been 13.00).
Measuring the dc offset is easy, set your dmm to "DC" and measure the dc on each channel (on the speaker terminals)....keep in mind when doing this measurement make sure you keep speakers and signal OUT (not connected). You'll quickly notice the measurement is within mV (so if your dmm goes to mv you should see 30mv or less otherwise you'll see 0.003v).
You should purchase Perry's Repair Amplifier Tutorial, its under 60.00 (almost what you paid in 4 transistors) and is worth every single penny. I use it all the time, very nice information...not to mention I get help from a friend (1moreamp) when I get lost.
Measuring the dc offset is easy, set your dmm to "DC" and measure the dc on each channel (on the speaker terminals)....keep in mind when doing this measurement make sure you keep speakers and signal OUT (not connected). You'll quickly notice the measurement is within mV (so if your dmm goes to mv you should see 30mv or less otherwise you'll see 0.003v).
You should purchase Perry's Repair Amplifier Tutorial, its under 60.00 (almost what you paid in 4 transistors) and is worth every single penny. I use it all the time, very nice information...not to mention I get help from a friend (1moreamp) when I get lost.
Jeanious, you're hurting me. I know I overpaid, but like I said, electronics stores around here are few and far between. Even Allied here in Canada wanted large $$$$ for them. Anyways, they are in and they work and the customer will pay. I was going to ask, is there a going rate for this work? What would most guys charge to diagnose and repair as I did? Is amplifier repair a dying thing and if so, what is taking it's place. I've only done a few but I enjoy it.
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