# Protection circuit on Lanzar Optidrive Plus 100



## Buickmike (Aug 10, 2012)

First post here. I am a big old school car audio fan. I try to collect what I can when I come across it. Anyway, I have an Optidrive Plus 100 that goes into protection mode without anything connected. If I connect power for the first time, it starts out in protection mode. If I power it off and back on, it will go green for about 3-4 seconds before going into protection mode. Here is the thing though. If I connect it to an audio source / speakers, it plays music just fine for those few seconds. I'm wondering if anyone here is familiar enough with these amps to help me narrow down where to look for a problem. The board looks good. I don't see anything glaring and all the big caps, diodes, transistors, resistors seem to test out fine. Any ideas?


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## Buickmike (Aug 10, 2012)

Well, I found the thermistor and it checks out fine. So at this point I know the amplifier section is ok and the thermal protection shouldn't be kicking in for any reason. That leaves me with the power supply. There was some prior surgery in that area, but I don't see any glaring issues. Right now I just can't figure out what the protection circuit is looking for. I know I could just send this off to get fixed, but I'm not ready to throw in the towel just yet.


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## Doc ProMos (Jul 1, 2012)

How are you checking the parts and with what..??.. Some stuff is better checked with power supplied and other stuff without power... also some parts need to be removed to be checked accurately (which can be a hassle) ... lastly the equipment used... are you using a multimeter with diode check capabilities and are you using an O-scope...??.. lastly posting some good pics of the inside helps tremendously.... Keith


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## Buickmike (Aug 10, 2012)

I'm using a multimeter that has diode check capability. Honestly, I am about as novice as you can get and am only trying to find issues such as completely open or shorted circuits. I will get pics later. A little hitory on this amp. I had this amp (this exact amp) in highschool (early 90's) running a pair of Lanzar Pro Plus 12's. One time it got hot and one of a pair of dioes on each side of the board fell out due to heat. I did a very poor job of soldering them back in and it worked. The guy who ended up with it just gave it back to me after all these years. I pulled the diodes and they seem to be ok. I replaced the big caps in that section to no avail. Not sure where to go from here.


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## Buickmike (Aug 10, 2012)

Here is a cellphone pic of the top of the board. Let me know if I should post a pic of the other side.


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## spooney (Nov 5, 2010)

I would think that you probably have a failed output transistor or output driver transistor. If the amp still powers on enough for the protect circuit to kick in then the power supply may be just fine. I had a Lanzar Opti 500 that had a similar issue as yours . It would power up,make a small click through the subs,maybe play a little low volume music , and then go into protect. I ended up rebuilding one channel of the 500 and she was fine after that. Made some loud and beautiful music


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## Buickmike (Aug 10, 2012)

spooney said:


> I would think that you probably have a failed output transistor or output driver transistor. If the amp still powers on enough for the protect circuit to kick in then the power supply may be just fine. I had a Lanzar Opti 500 that had a similar issue as yours . It would power up,make a small click through the subs,maybe play a little low volume music , and then go into protect. I ended up rebuilding one channel of the 500 and she was fine after that. Made some loud and beautiful music


All of my transistors ohm out identically. Not sure if that means they are good or not.


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## ATOMICTECH62 (Jan 24, 2009)

Its most likely an old leaky cap causing just enough DC offset to kick it into protection.
A PITA to find the bad one.Its usually a small one in the preamp section.


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## Buickmike (Aug 10, 2012)

Thanks. I was thinking it was a cap due to the fact that it will work just fine (music plays great) for a few seconds before going into protection mode once I power it up once and let them all charge. No signs of leakage, so they could be dried out. I was hoping it was one of the larger ones, but replacing them did not help. I had an issue with my HDMI board on my Onkyo receiver and it turned out to be all the small caps. I have 20 smaller electrolytic caps on this board. Luckily there are about 3 different types, so if I can test similar ones against each other and hopefully narrow down a bad one.


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## Buickmike (Aug 10, 2012)

I pulled the mosfets off of the power supply section and they all check out just fine. The reason I did that is because I followed some leads off of those that went back to a IC that connects to the IC for the protection circuit (as far as I can tell). I was able to properly check the diodes rest of the parts in that circuit with them off and they are ok. At this point I think it has to be one of the small caps on the board. My main worry at this point is that I will pull them all and think they are ok because they seem to drain when I check them with an ohm meter. If one is simply draining off too fast I'll never notice. Arrrrrr....


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## Buickmike (Aug 10, 2012)

I pulled all the output transistors and checked them with my multimeter. I didn't find any "how to test transistor" articles that matched what I was seeing with these when I checked them with the multimeter. I did have OL on all but 2 combos when testing them in diode mode. From what I've read, that is what should be expected on a bipolar transistor. What was odd is that the 2 that gave me a reading were around 550 ohms. Since they all tested out identically I'm assuming what I found was normal. If these were all bad I wouldn't be getting good music out of this thing for those few seconds. 

I tested all the small caps on the board and I didn't find any that were open or shorted. I don't know what to do at this point. I guess I could start replacing all the little caps incase one is just not holding its charge and is causing all this, but I really don't know if it is worth my time. I scored an Opti Drive 50 plus on Ebay, so now I have a nice pair to go together so I am more motivated to fix this thing. Thoughts?


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