At this point I am just going to do as instructed because quite frankly, I don't know what to do next.
Remove the gate resistors for the power supply FETs and confirm that you read infinite resistance from leg 1 to the other two legs.
Did you buy any extra 3205s?
Did you buy any extra 3205s?
Unfortunately I did not buy any extra 3205s. I will fire up the weller and remove R19 and R20.
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Have you ever replaced the transistors like the driver transistors before?
Did you have an IRF540 that was still good?
Did you have an IRF540 that was still good?
If I'm correct and the driver transistors are Q4 and Q5, I haven't ever changed them.
I changed the IRF540s. I don't know if they are defective now or not? They are in circuit but, not shorted. Is the 540 a power supply transistor? I've been reading your tutorial today but, I'm still not clear on which are output transistors, driver transistors, etc.
The IRF540s and 9540s are the output transistors.
Q1, 2, 4 and 5 are the driver transistors.
I was asking about the small surface mount transistors to see if you had any experience replacing that type of transistor.
The 540 is not typically used as a power supply transistor but is an FET and could be used temporarily in place of the blown 3205 to allow further testing/troubleshooting.
If you want to order the parts that are likely to get the amp working and risk having to order again, you can do that. It may be possible to use a remaining 540 in the supply and shuffle one or two SMD transistors to repair the PS drive circuit to get the amp running to a point to determine what else is wrong.
Q1, 2, 4 and 5 are the driver transistors.
I was asking about the small surface mount transistors to see if you had any experience replacing that type of transistor.
The 540 is not typically used as a power supply transistor but is an FET and could be used temporarily in place of the blown 3205 to allow further testing/troubleshooting.
If you want to order the parts that are likely to get the amp working and risk having to order again, you can do that. It may be possible to use a remaining 540 in the supply and shuffle one or two SMD transistors to repair the PS drive circuit to get the amp running to a point to determine what else is wrong.
I don't have experience replacing the small ones. I take it that it's not all that simple?
Is it possible I could order enough extra stuff to replace anything that might be wrong or, would that be too expensive?
I guess I would ask what you recommend here?
IF you don't have any good 3205s, see if you have a good 540 that you removed.
If you do, remove the driver transistor that was defective.
Add new solder to the legs of the transistor. Heat the two legs on the bottom for a couple of seconds then quickly move the iron to the top terminal and slide the transistor off of its pads.
Check Q2 if Q4 was defective. If it's OK, continue below.
You can move one of the protection circuit transistors like Q107 or Q117 to the driver position.
Then connect only ground and remote and confirm that you have approximately 4-5v on the emitters of all of the driver transistor.
If you do, remove the driver transistor that was defective.
Add new solder to the legs of the transistor. Heat the two legs on the bottom for a couple of seconds then quickly move the iron to the top terminal and slide the transistor off of its pads.
Check Q2 if Q4 was defective. If it's OK, continue below.
You can move one of the protection circuit transistors like Q107 or Q117 to the driver position.
Then connect only ground and remote and confirm that you have approximately 4-5v on the emitters of all of the driver transistor.
I do not have a good 540. Would an IRFZ44 work? I ordered one for that Optimus amp that I have had sitting around for a few years.
Ok, so far I have removed Q6. I removed Q4. I removed Q117.
You say check Q2. Do I need to have it powered to do that? Can I check Q117 now that I have it off the board?
In diode check mode. Black lead on the collector. Red lead on base. It reads 754. Don't know if that means a darn thing. Red on collector, black on base read 1 or open.
You say check Q2. Do I need to have it powered to do that? Can I check Q117 now that I have it off the board?
In diode check mode. Black lead on the collector. Red lead on base. It reads 754. Don't know if that means a darn thing. Red on collector, black on base read 1 or open.
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On the repair tutorial page, there is a section labeled 'checking bipolar transistors'. You should read approximately the same for your transistors. The ones marked 1A are NPN transistors. The ones marked 2A are PNP transistors.
I did find that. It said between .5 and .7V so, .754V seems ok.
Will the Z44 survive for testing with just the legs soldered into the holes or, will they heat up like they do when B+ is applied? I ask because it would be much easier to attach it temporarily.
Will the Z44 survive for testing with just the legs soldered into the holes or, will they heat up like they do when B+ is applied? I ask because it would be much easier to attach it temporarily.
0.75 is high. Did you read approximately the same base to emitter and base to collector?
You can test various other transistors with the same markings to see what they read.
The Z44, especially with no B+ connected will not get hot. If you don't solder it down, you'll need to monitor its temperature closely when B+ is connected.
If you don't have a current limiter, you'll need a small fuse (~5 amp) when you connect B+ (at a later time).
You'll also need to set the bias pots fully counter-clockwise (important later when the amp is powered up with B+).
You can test various other transistors with the same markings to see what they read.
The Z44, especially with no B+ connected will not get hot. If you don't solder it down, you'll need to monitor its temperature closely when B+ is connected.
If you don't have a current limiter, you'll need a small fuse (~5 amp) when you connect B+ (at a later time).
You'll also need to set the bias pots fully counter-clockwise (important later when the amp is powered up with B+).
Yes, I tested the same from base to emitter and base to collector. Supposedly that was a good one that came from position Q117.
I can solder down the Z44 or if we decide to order 3205s, I can change it back to that. I was just hoping for testing purposes I could get by with temporary install on it.
Aren't the bias pots the ones your tutorial says not to mess with unless you know what you're doing?
Q2 is .823V That's too high. The top of it looks a little bulged too.
Q118 is .697 collector to base and .753 base to emitter.
Q118 is .697 collector to base and .753 base to emitter.
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If you replaced the output transistors, the old bias settings are not reliable and could cause the new outputs to overheat and fail. Setting them full CCW sets the bias as low as possible so it isn't a problem during testing.
By 'tutorial', are you referring to the online material?
When you tested the PNP driver, what did you get B-C and B-E?
By 'tutorial', are you referring to the online material?
When you tested the PNP driver, what did you get B-C and B-E?
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