Hi, I am trying to fix the amp board on REL q201e subwoofer. The transistor BF469 and zener diode got completely burned off. The transistor BF469 and BF470 are no longer available. What other equipment part can be substituted for this??
-Max
-Max
Now EOL ksa1381 or ksc3503 if you can find them.
Or kta1381, ktc3503 from profusion in the UK that are authorized to sell KEC. Ive tried them in my designs and they work fine
Or kta1381, ktc3503 from profusion in the UK that are authorized to sell KEC. Ive tried them in my designs and they work fine
Farnell (the UK division of Newark) list the BF469 and BF470 in stock from Multicomp Pro which I believe is their in house low cost brand. But if I change the Country/Region to USA the Newark web site search doesn't find them. I don't know if they can be bought in the USA and also don't know if they are OK or not.
Any modern driver type of sufficient voltage, even flipping a TO-220 around. A subwoofer application isn’t some place where you have to worry if Cob is larger, either.
Multicomp literally could be anything similar. Usually they are second source from one of the Taiwan makers. Most of that stuff is actually pretty good. Ones I’ve used in the past have always worked. But worked and being a perfect replica are not necessarily the same. If you were expecting a 12 pF Cob, you might get the usual 20-30.
Multicomp literally could be anything similar. Usually they are second source from one of the Taiwan makers. Most of that stuff is actually pretty good. Ones I’ve used in the past have always worked. But worked and being a perfect replica are not necessarily the same. If you were expecting a 12 pF Cob, you might get the usual 20-30.
It looks like I have a lot to learn. I am going to order TTA004/TTC004 and MJE340/350 pairs and see how it goes, they are readily available from DigiKey. If it blows up, it's no big deal as it's already blown up in smoke 🙂. You are right, BF469/470 are available in other countries - also in Japan so I can order next time I visit my folks.
I'm guessing smaller Cob is better? I see BF469/470 are 1.8pF.
Thank you so much for suggestions!
-Max
I'm guessing smaller Cob is better? I see BF469/470 are 1.8pF.
Thank you so much for suggestions!
-Max
Well... it smoked again! I ended up sourcing BF469 (whopping $13 on eBay!), from the looks of it, it seems like a legit Philips part. However, when I put everything back together, the same part started to heat up and smoke. I can see that solder joint is melting. I think it's back to the original problem.
What do you think the problem is? Do you think one of the output device mosfets are bad?? I checked all the leads on all the mosfets but there is no obvious shorts. So far I've replaced all the electrolytic capacitors, burned zener diode and some resistors that looked like burned. I also checked all the parts on the board for obvious shorts but there were none.
I have no idea where to go from here, please help!
-Max
What do you think the problem is? Do you think one of the output device mosfets are bad?? I checked all the leads on all the mosfets but there is no obvious shorts. So far I've replaced all the electrolytic capacitors, burned zener diode and some resistors that looked like burned. I also checked all the parts on the board for obvious shorts but there were none.
I have no idea where to go from here, please help!
-Max
You have to desolder and test the output transistors. You can do it using a multimeter, but I highly recommend getting one of those little Chinese component tester. Incredible value for $21!
https://www.amazon.com/Multi-Functi...ransistor/dp/B081K4CM1F/ref=asc_df_B081K4CM1F
https://www.amazon.com/Multi-Functi...ransistor/dp/B081K4CM1F/ref=asc_df_B081K4CM1F
I removed all 4 output transistors and they all seem to be okay. One of them behaves a bit different, the resistance between drain/source is slightly higher when I apply a voltage on the gate. (~100 ohms instead of 10 ohms). Is this the issue?? It is IRFP240.
Is it okay to power on the amp board without the output transistors?
-Max
Is it okay to power on the amp board without the output transistors?
-Max
How much voltage do you apply to the gate? Even 10ohm is way too much if it’s fully on. Should be 0.18ohm according to the data sheet. There’s a simple way to test MOSFETs using the diode setting on the multimeter. This is how:
MOSFETs usually fail short, so they might be OK. But you should check them anyway.
MOSFETs usually fail short, so they might be OK. But you should check them anyway.
Hard to find components from eBay are almost certainly fake. Get some TTA004B/TTC004B instead. Very easy to find from reputable vendors like Mouser. I just used them in a build with 55V rails and they work great.
On this side of the universe it’s easier to get the Toshiba parts. Are there any authorized CDIL distributors over here? I’ve never heard of one. The only CDIL parts I’ve uncovered over here are from surplus houses - and you know what most people think of that practice.
It still smokes! I have replaced the burning BF469 and non-burning BF470 with MJE340/MJE350 pairs and also all the output MOSFETs but collector and base of MJE340 (NPN) smokes once I turn on the amp board. I managed to measure some voltages: emitter and base is 3V and collector is 60V on MJE340 but -16V/-60V respectively for the MJE350. I think the 3V applied on the base of MJE340 is not enough?? What would cause the NPN transistor to smoke?
Originally, there are total of 3 BF469/BF470 pairs on the board. 2 pairs by the output MOSFETs - all the leads on 2 pairs are 60V/-60V (is this okay?) and 1 pair near the volume pots (both have 10uF capacitor, 2kohm resistor and zener diode near them.) One by the volume pot is the one smoking. What is the function of the pair by the volume pots? I can provide pictures later on once the capacitors are discharged.
Thanks all for your inputs.
-Max
Originally, there are total of 3 BF469/BF470 pairs on the board. 2 pairs by the output MOSFETs - all the leads on 2 pairs are 60V/-60V (is this okay?) and 1 pair near the volume pots (both have 10uF capacitor, 2kohm resistor and zener diode near them.) One by the volume pot is the one smoking. What is the function of the pair by the volume pots? I can provide pictures later on once the capacitors are discharged.
Thanks all for your inputs.
-Max
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Hello
The maximum base current (IC) of MJE340 is 0.5A vs 1A for BF469, this may be the reason for the current issue.
Best regards.
The maximum base current (IC) of MJE340 is 0.5A vs 1A for BF469, this may be the reason for the current issue.
Best regards.
I think the current is supposed to flow through the NPN transistor from collector to emitter when it is on but for some reason it is not flowing through the emitter hence all the current is going to the base - this heats up the transistor as only a small current is allowed to the base. I now have to figure out why current is not flowing through the emitter. I’ll have to draw a schematic from reverse-engineering.
-Max
-Max
Seems like another fault is not being found. So it will keep eating transistors.
After output faults the flyback voltages might have taking out any VI limter transistors/diodes
in that circuit, or any previous gain stage. Diode test any semiconductor for open/short transistors
an any excessive high resistor values/shorts
After output faults the flyback voltages might have taking out any VI limter transistors/diodes
in that circuit, or any previous gain stage. Diode test any semiconductor for open/short transistors
an any excessive high resistor values/shorts
Correct, I suspect another issue.
There are 3x LM324N chips on the board. I believe there is 4 opamps in one chip. Do you know how they will fail? And how to check them? I couldn’t find obvious shorts
There are 3x LM324N chips on the board. I believe there is 4 opamps in one chip. Do you know how they will fail? And how to check them? I couldn’t find obvious shorts
LM324s are pretty bomb proof as long as you don’t expose them to voltages above the stated maximum.
They’re not as straightforward to test as transistors. To test them out of circuit, you need to put them on a breadboard and wire them up as voltage amplifiers. You can test them in circuit by comparing the inputs to the outputs and doing some math. How are they wired up? You have a schematic?
They’re not as straightforward to test as transistors. To test them out of circuit, you need to put them on a breadboard and wire them up as voltage amplifiers. You can test them in circuit by comparing the inputs to the outputs and doing some math. How are they wired up? You have a schematic?
Okay. I measured Vcc voltages on LM324Ns which are supplied by the emitters from MJE340/350 pairs and Vcc+=3V and Vcc-=-16V. I think this is wrong. Now I know the functions of those devices! They are used to regulate the supply voltages to LM324Ns.
But I don’t know which one is wrong. Emitter having +3V is the one which is heating up. By looking at the datasheet of LM324N, allowed supply voltages are +-3 to +-16. The voltage regulator diode that I replaced is 3.9V because the negative one had y55 marked on it but perhaps it is y5, in which case it is 16v zener diode. What do you guys think?
I do not have the schematic, I don’t think REL released them.
-Max
But I don’t know which one is wrong. Emitter having +3V is the one which is heating up. By looking at the datasheet of LM324N, allowed supply voltages are +-3 to +-16. The voltage regulator diode that I replaced is 3.9V because the negative one had y55 marked on it but perhaps it is y5, in which case it is 16v zener diode. What do you guys think?
I do not have the schematic, I don’t think REL released them.
-Max