| spooney |
| picked this amp up cheap from somebody online knowing it didn't work.I don't see any fried components and the fets and output transistors all appear ok.This amp will not turn on at all.this is the first time i've ever tried to troubleshoot an amp with a problem of this nature.I was hoping maybe Perry or someone else could maybe point me in some directions. |
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| Perry Babin |
If the amp won't power up, confirm that you have power to the FETs and the third leg of the FETs is grounded.
If those are OK, post the power supply IC number and the voltages on the pins. |
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| spooney |
| The FETS all appear to be ok but I'm getting no voltage on any of the pins of the c494 IC. |
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| Perry Babin |
What's the DC voltage on the 3 pins of Q101?
What's the DC voltage on the base of Q403?
Check these with power applied to the amp (including remote). Use the ground terminal as the reference (black meter lead connection). |
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| spooney |
| on pin 1 of Q101 i've got 12.7 volts , pin 2 has .4 volts but slowly drops , and pin 3 has 12.7 volts as well. As for Q 403 I'm unable to find it so far.Could it possibly be Q405? |
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| spooney |
| quick question for you Perry.This amplifier internally consist of three seperate boards.Theres the main board,the preamp board,and a small board near the fan.Do I need to have the fan board plugged in to get proper measurements from the amp or can I leave it unplugged as it makes it difficult to work on with all three boards plugged together |
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| Perry Babin |
Doesn't the fan board have the gain controls?
If so, the gain may be very low without it.
If you try it, make sure that you have a relatively small fuse or current limiter in line with the B+ source. Sometimes, when components are removed from a circuit, the circuit becomes unstable and oscillates (which could cause damage to the amp). I don't think it will happen here but you should be careful when you initially power it up. |
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| spooney |
| was the voltage on Q101 what I should be expecting?And what about that Q403?I don't see it on the board.I see a Q405 though. I've yet to get this amp to actually power up. |
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| Perry Babin |
Sorry I missed one of the posts. I only read the last one.
The center leg should have ~12v on it but the transistor (Q101) is not being driven on by Q403 (small surface mount transistor near Q101). When properly driven 'on', the voltage on the third leg will be ~0.6v less than the voltage on the first leg and the voltage on the first and second legs will be nearly identical. |
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| spooney |
| ok i think i see it now.I'll get some voltage measurements from it and check back.Thanks Perry |
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| spooney |
| which lead is the base on that transistor perry?I see two leads on one side and only one lead on the other.The side with one lead i'm getting 12.7 volts and two leads on the other side i'm getting nothing. |
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| Perry Babin |
| What is the voltage on the 3 terminals of Q103? |
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| spooney |
| is Q301 another surface mount transistor?None of the surface mounted parts are labeled on the circuit board of this amplifier.Is there a capacitor or some other part it is near that would help me find it? |
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| Perry Babin |
| Sorry about the typo. I originally wrote 301. It's Q103. |
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| spooney |
| alright leg one has .68 volts , leg two has 12.7 volts , and leg 3 has 1.1 volts |
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| Perry Babin |
What's the voltage on the 3 legs of Q404?
What's the voltage across D301?
So I don't forget to tell you later...
You don't need to remove D301 for the tests above but if it's defective and you remove it later, do NOT apply power to the amp with it out of the circuit. |
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| spooney |
| not seeing either one of those.Is it Q 405 possibly? |
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| spooney |
| okay i found d301.it was hidden under some silicone near a capacitor.am i measuring with the black lead on ground still? or one lead on each side of the diode? |
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| Perry Babin |
| One lead on each side of the diode. |
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| spooney |
| .93 volts across d301.Is Q404 a surface mount part near d301? |
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| Perry Babin |
Yes.
It's likley that the diode or C301 is leaking (electrically).
Get the readings off of the transistor. If the top terminal is at 12v and the emitter (right terminal on the bottom of the transistor) is ~1/2v below the voltage on the diode, pull the diode out and check it.
Do NOT apply power with the diode out of the circuit. |
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| spooney |
| okay well i found Q404 and it is fried.You can easily see its been burnt.The side that only has one leg i'm getting 12.6 volts. If i'm looking at the part with the two legs facing down the right leg is at 1.1 volts and the left leg is at 12.7 volts . I'm getting a short between the top leg and the bottom left leg. |
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| Perry Babin |
Something isn't right. One side of the diode should be grounded. If you have only 0.93 across the diode, the diode either isn't grounded or there is an error in the way the voltage was measured.
Check to make sure that the striped side of the diode is connected to the left leg of Q404.
Make sure that the unstriped side of the diode is connected to chassis ground.
If the top and left legs of Q404 are shorted together, The diode is VERY likely damaged. It's a 6.2v Zener. |
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| spooney |
| i checked and rechecked and i still get the .93 volts no matter what side of the diode the leads are on.One side of it is grounded and the other side (striped side)connects to what used to be the left lead of Q404.There is also another small surface mounted part tapped off of the trace that runs from the diode to the leg of Q404. I'm not sure if it is a resistor or what but one side of it is tapped off of the trace from the diode to the left leg of Q404 and the other side runs to the top leg of Q404.By the way do you happen to know a part number for what q404 was?Its completely destroyed? |
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| Perry Babin |
Q404: 2sc2412k
R403 is connected between the top terminal and the left terminal. It's a 10k resistor.
You should pull and check Q102 and Q103. Also check R404 and R405.
Order a new zener when you order the other parts. I'd suggest ordering a few extras of all of the parts. |
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| spooney |
| hey Perry do you happen to know the wattage rating on that zener diode? |
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| Perry Babin |
| I'd guess it's a 1/2 watt. There's no reason for it to be a 1 watt. |
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| spooney |
| Perry do you happen to know the value of c301?I'm putting together a parts order but i don't have the amplifier right here in front of me. |
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| spooney |
| okay well i replaced q404 and the diode so far and still no juice.I measured 6.15 volts across the diode ,6.15 volts on the bottom left leg of q 404, 12.75 volts on the top leg of q404, and 5.57 volts on the bottom right leg of q 404. Are these numbers in order? and if so where should i look from here? |
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| Perry Babin |
On Q102/103 you should have (approximately)...
Pin 1: 5v
Pin 2: 12v
Pin 3: 5.6v
You should also have 5v on the VDD pin of the processor. If you have a scope and a 10x probe, you should see oscillation on the Xin/Xout pins of the processor. |
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| spooney |
the voltages on q 102 and 103 are close on the outside pins but the middle pin on both of them is sitting at a little under 9 volts.
Which processor are you talking about Perry?Are you talking about the square one under the foam pad or are you referring to the 494? I do not own an oscilloscope but is there any other test i can do? |
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| Perry Babin |
As long as the voltage on the first pin is very near 5v, the center pin isn't too important.
The processor is IC8 (the one with 40+ leads).
You could also check the voltage on pin 30 of the processor.
Do any of the indicators light up? |
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| spooney |
| is 4.85 volts close enough to 5 or should it be higher? If i'm reading the leads correctly pin 30 has .015 volts on it but pin 28 has 4.85 volts on it. I see the board is labeled with a 1 which i assume is pin one of the processor.I just counted up to 30 and used that as pin 30, please tell me if this is correct. None of the indicators light up. |
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| Perry Babin |
4.85 should be OK.
What's the voltage on pins 5 and 6 of the processor?
You can confirm the pin numbering by using the ground pin (pin 17) as a reference (confirm continuity to ground). |
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| spooney |
| okay 17 is definitely the ground so i think i'm good on the numbering. Pins 5 and 6 have almost nothing. .002 and .001 respectively. |
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| Perry Babin |
| What's the voltage on pins 18-21? |
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| spooney |
pin 18 4.8 volts
pin 19 .116 volts
pin 20 .176 volts
pin 21 .002 volts.
when the amp is first powered on i'd see almost nothing on the pins.Then after about 15 seconds they would all jump up and stay up for about another 15 seconds and then drop right back down to nothing and stay there.I re-checked 5 and 6 and they do the same thing. 6 will be at 4.8 volts for about 15 seconds and then drop and 5 really never has much either way , about .015 and then .001 when it drops down. |
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| Perry Babin |
Everything is probably jumping up because you don't have a good ground reference point for your meter. If you use the ground pin of the processor, do you get the same readings?
6 may be going up because the voltage on your supply is dropping when you try to power up the amp.
When you try to power the amp up, does pin 30 go to ~5v for a few seconds (using the ground pin of the processor for the reference)?
What's the voltage on pins 35-37?
By the way, I'm not just having you check random points. I'm working my way through the various inputs. It would be nice if you had a scope and could check for oscillation on the xtal pins. You didn't happen to buy one in the last few days did you? :) |
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| spooney |
| no unfortunately i didn't get a scope. I really need to just bite the bullet and drop the money on a decent scope. It would help me repair a few amps i'm sitting on at the moment,including my orion 2150gx. |
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| spooney |
pin 35 4.83 volts
pin 36 4.83 volts
pin 37 .017 volts
These all stayed constant. I rechecked the other pins using the ground of the processor and the results did not change for those pins.they would still start out low jump up and then go back down. |
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| Perry Babin |
37 needs to be high.
Post the voltages on Q406, Q407 and Q408. |
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| spooney |
| can you give me an approximate location on those devices Perry? I think I've found them but none of the SMD parts have any designations next to them to let me know what is what and i have no schematic.Does the remote turn on signal run into this trio of transistors through a resistor and two diodes? |
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| Perry Babin |
| See attached. |
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| spooney |
cool turns out I found the right ones.The voltages are listed as follows assuming the single lead is the top of the transistor:
bottom left,top middle,bottom right
Q406 1.908,.019,.002
Q407 .002, 1.908, .002
Q408 .002 on all legs |
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| Perry Babin |
Q408 may be shorted. Check it with your meter set to ohms.
If it's not shorted, post the voltage across D303 and R73 (on the other board near the remote/p.con terminal). |
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| spooney |
| if q 408 is shorted its not completely shorted.Reading about 3 k ohms from top lead to either bottom lead with it in circuit. D 303 with meter leads on either side of it is at 12.6 volts and R73 with leads on either side of it reads nothing. |
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| Perry Babin |
D303 is a 7.5v Zener. If it has 12+ volts across it, it's open. If you jump the zener out (solder a wire across it), the amp may power up.
There is a 3.3k resistor from the top terminal to the right terminal (collector to emitter) of Q408 so 3.3k is normal. Check to make sure the bottom two terminals are not shorted together. If they are, remove the transistor from the circuit. |
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| spooney |
| d 302 is seeing 12 plus volts so should i replace that as well or is that diode a different voltage rating?Is it safe to try to power it up with wire soldered in place of those diodes as long as i make sure nothing gets shorted(like a power wire or something).I have some 6 volt zeners lying around will those work or do i need the 7.2? |
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| Perry Babin |
D302 is a 15v zener and is used to shut the amp down when the voltage goes above ~16v.
D303 prevents the amp from turning on when the remote voltage is less than ~8v.
A 6vZ will work but you should replace it with the correct part before the amp is put back into service. |
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| spooney |
| i'm ordering a few things from mouser anyways so i might as well stop being cheap and get the right parts. |
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| Perry Babin |
| Use the 6v to see if you can get it to power up. If you find you need other parts, you can order them when you order the correct zeners. |
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| spooney |
| well i soldered in the 6.2 volt zener in today and i'm happy to say that the amp finally works.This is by far the most troubleshooting I've ever had to do or I should say that Perry had to do for me :) I'd given up on this thing so many times.It feels good to finally get it going.All i need is that 7.5 volt zener and some terminal screws and i'll be able to finally put this thing to bed. |
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| spooney |
| The 7.5 volt zener is in and so far all seems well.I've got this amps bigger brother on the way and with any luck i'll get that one going as well and have a nice pair of amps for my car. |
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