amp protection mode ?

[chrissy14xsi]

hi all im looking for a little help on my car amp its a vibe slick a0 and the wires from my sub came of now my amp is in protection mode is there any way i can sort it

 

[jol50]

Does it protect with no sub hooked up?

 

[chrissy14xsi]

yeah even when i disconect the sub and rca cable s it still protects

 

[Perry Babin]

If it went into protect mode with the speaker wires disconnected from the amp, it likely has shorted output transistors. If you want help in repairing it, post a photo of the inside of the amp.

 

[chrissy14xsi]

ok got one here if you need any close ups or anything removed let me know thanks

An externally hosted image should be here but it was not working when we last tested it.

 

[jol50]

That looks familiar. The largest transistors clamped to the sink, the pair on each side (top/bottom in photo), are the outputs. First thing you can do is see if any two of the three legs are shorted together for each one. If not do the same for the smaller ones near the transformer, upper right on the sink in the photo.

 

[Perry Babin]

On the top and bottom of the photo, you can see two large transistors under the black clamps. Measure the resistance from leg 2 to leg 3 (see attached for numbering scheme). Do any read near 0 ohms?

 

[chrissy14xsi]

ok im a novice but im sure il get there they all look fine nice and new no burns etc.i have a ammere what do i set it to and where do i put the black and red probes on wich legs.they are lettered b c and e if thats any help

 

[chrissy14xsi]

ok think i sussed it i put the red probe on c and black on e for each of the four and set the meter to diode .[pic] top left= 490 top right =003 bottom left=1265 bottom right =523

 

[Perry Babin]

003 is shorted. Pull it out of the board and test it. If it still reads near 0, it is defective and will have to be replaced. What are the numbers on the transistor?

As a side note...
Do not power up the amp without having the transistors clamped down.

 

[chrissy14xsi]

K
D998
O 740

 

[Perry Babin]

KTD998 is the part number. You should also replace the KTB778 next to the shorted one.

If you can't find them in the UK, B&D has them.
http://www.bdent.com/search/search.jsp?contains=ktd998&category=ALL&submit.search=Search!

 

[chrissy14xsi]

ok thanks got another question is it just leg 2 and 3 as when i do it on legs 1 and 2 on the bottom right i get a 002 also i had the sub bridged between the 2 positive conections if that makes any diference

 

[chrissy14xsi]

hi i also tried getting one from my local electronic shop as i phoned him but dont think the guy had much of a clue he says i can use one similar spec

www.maplin.co.uk

 

[Perry Babin]

Pull it and check it. If it's still shorted, replace all 4 of them.

Sometimes, parts with similar specs will work. Other times, they require minor re-engineering of the circuit to get them to work.

 

[jol50]

Littlediode.com shows a 2SD998, IIRC they are in UK, if that is the same. I bought some STK and other stuff from them a while back that seemed ok.

Don't say what brand it is: http://www.littlediode.com/components/2SD998_Transistor.html

 

[Perry Babin]

The 2S parts appear to be the same part as the KT parts. In general, the 2S prefix and the KT prefix are interchangeable but not always.

 

[chrissy14xsi]

ok so its a 50 50 wether they work or not. why are they so hard to get? ive been looking all over since i got home

 

[Perry Babin]

Since you had one fail shorted from 1-2, you need to check the driver transistors. They will likely have their first leg directly connected to the first leg of the output transistors (the large ones clamped to the heatsink).

You'll have to remove them from the board to check them. If you're not sure how to check them, use the form on the following page.
http://www.bcae1.com/repairbasicsforbcae1/images/transistortestpage02.html

Post the screen caps of the readings you get for each of the 4 driver transistors.

There likely a resistor connected between the first leg of each of the outputs in each pair. You need to make sure it's not out of tolerance. With the outputs out of the board, measure the resistance between the solder pads for leg one of each output in each pair. It should be between 100 and 330 ohm. Do this for the top pair and the bottom pair of outputs. Is the resistance the same top and bottom?

 

[Perry Babin]

If you were in Korea or China (where this was likely produced), it would probably be easy to find them.

There's better than a 50/50 chance that the 2S parts will work. I'd say there's a 99% chance that they'll work perfectly.