I checked all 3 legs.
Top single leg: .4 m ohms
Bottom left leg: .618 m ohms
Bottom right leg 18.03 m ohms
I checked it with the one in the other channel and both have identical readings.
Did I provide what you need?
Top single leg: .4 m ohms
Bottom left leg: .618 m ohms
Bottom right leg 18.03 m ohms
I checked it with the one in the other channel and both have identical readings.
Did I provide what you need?
Q223 is a BJT, not an FET. Look up the datasheet if you're unsure what a particular transistor is.
Ok did some quick research:
FET= Field effect transistor which is a voltage controlled valve where the gate-sorce voltage controls the drain current.
BJT= Bipolar junction transistor which is a current controlled valve where the base cuurent controls the collector current. The bas is always the same but the emitter and collector change from NPN to PNP.
They do seem to correspond roughly.
So the base on Q223 would be the top single leg which had the reading of 0.4 ohms.
I now know the difference but without a schematic would not have known that, as to why a schematic is very important when repairing amps. So if a FET was put in place of a BJT could this cause the problem I am seeing?
I replaced the Q223 awhile back but used a MMBT 3904 which I believe is a FET and not a BJT.
Is there any way other than a schematic to identify a FET vs BJT when the markings on the case both say 1AM?
I had a birthsheet from a Power 360a2 years ago that showed 580 watts rms bridged.
The SMD Code Book
You have to measure the cases in some instances to know which case style you have. For that, you'll need a dial or digital caliper. It's also possible to have confusing markings which make it difficult to know with 100% certainty what the part is so there's a bit of guesswork sometimes.
You have to measure the cases in some instances to know which case style you have. For that, you'll need a dial or digital caliper. It's also possible to have confusing markings which make it difficult to know with 100% certainty what the part is so there's a bit of guesswork sometimes.
So my question remains if I replaced a BJT with a FET would it or could it cause the problems I am seeing? Valves controlled by current and voltage would operate very differently would they not??
Do you think that you installed the wrong part somewhere?
Where?
What part number (original and sub)?
Where?
What part number (original and sub)?
I have had some of these amps for years from when I first started repairing and lacked ALOT of knowledge. Back then I would steal parts from other amps that had the same markings and replace stuff.
Q223 which is marked 2 A and you said is a BJT
I replaced it with a 2 A from mouser part # MMBT 3906 which I would assume is a FET.
In the other channel it would be the same part as Q123 which is marked 2 A.
So thats why I was wondering how to identify them. Some are marked 1AM and some are marked 1A.
For instance like the 4 driver transistors by the PWM chip. Sometimes they are marked 1A, sometimes 1AM, sometimes 1G.
Datasheet for 3906:
http://datasheet.octopart.com/MMBT3906-Fairchild-datasheet-23394.pdf
It states that it's a PNP transistor. PNP and NPN transistors are BJTs. N-channel and P-channel transistors are FETs.
In general, all SMD transistors commonly used in car amps are BJTs. There are a few JFETs that are SMDs but they're relatively rare (Xtant and MTX class D amps, mainly).
The markings are sometimes confusing. In general, the SOT-23 transistors (used in Rockford amps) with a 1 prefix are NPN transistors. Those with a 2 prefix are PNP transistors. That doesn't mean that all 1x transistors or all 2x transistors are interchangeable but it gives you an idea of what the transistor is and how it's being used when troubleshooting.
http://datasheet.octopart.com/MMBT3906-Fairchild-datasheet-23394.pdf
It states that it's a PNP transistor. PNP and NPN transistors are BJTs. N-channel and P-channel transistors are FETs.
In general, all SMD transistors commonly used in car amps are BJTs. There are a few JFETs that are SMDs but they're relatively rare (Xtant and MTX class D amps, mainly).
The markings are sometimes confusing. In general, the SOT-23 transistors (used in Rockford amps) with a 1 prefix are NPN transistors. Those with a 2 prefix are PNP transistors. That doesn't mean that all 1x transistors or all 2x transistors are interchangeable but it gives you an idea of what the transistor is and how it's being used when troubleshooting.
Ok that is good info to know. Thanks for your time and research in that matter, I appreciate all your help.
I just wish I could figure out where that dc is coming from on that channel. Sometimes these little amps are harder than the bigger amps to repair. I guess a good start would be to download the schematic first thing on every amp you work on. I have a few laying around that are still kicking my butt. 9/10 rockford amps are quick repairs. Usually its a shorted channel or power supply. This little stuff can be very tedious work. Now I know why people charge so much (flat-rate) to repair amps.
I just wish I could figure out where that dc is coming from on that channel. Sometimes these little amps are harder than the bigger amps to repair. I guess a good start would be to download the schematic first thing on every amp you work on. I have a few laying around that are still kicking my butt. 9/10 rockford amps are quick repairs. Usually its a shorted channel or power supply. This little stuff can be very tedious work. Now I know why people charge so much (flat-rate) to repair amps.
Look at the datasheet for the 3904 I posted so that you can see which terminals are the base, collector and emitter. Then measure the DC voltage from the source of one of the IRF540s to the base and emitter of Q223.
In the future, if you're not 100% sure of something, ask.
In the future, if you're not 100% sure of something, ask.
Black probe on source of IRF540 red probe on base and emitter of Q223
Base: 2.142 vdc
Emitter: 2.778 vdc
If I reverse the probe configuration the numbers read the same they just change to - vdc.
Any thoughts?
Ok thank you for the info I see your just 40 min south of me as well. What is your e-mail?
Last edited:
- Status
- Not open for further replies.