Hello,
I have here a Teac BX-500 amp that was pretty much mistreated by the previous owner before i picked it up from the scrap yard. Some components are missing, there are visible burn marks on the PCB, many tracks are torn off or have been repaired provisionally, there are small holes drilled into the PCB (wtf?!), and the heat sink is bent and drilled in various places. I don't think, it's economically viable to fix this device, but I really enjoy the Design and I want to learn more about power amplifiers and that would be a good way to do so I think. Meanwhile I have listed all missing parts, for most of them I have found a replacement, but with the transistors, especially in the power amplifier, some are defective or missing, here I would need advise, which transistors can be used as replacements, because the originals aren't available anymore and I've already fallen for Fakes ...
Q111: 2SC1815 (GR)
Q112: 2SA949 (Y)
Q116: 2SD718 (O)
Q117: 2SB688 (O)
Q211: 2SC1815 (GR)
Q214: 2SC2235 (Y)
Q215: 2SA965 (Y)
Q216: 2SD718 (O)
Q217: 2SB688 (O)
Q218: 2SC2240 (GR)
Is it possible to use 2SC5200 and 2SA1943 for Q116/117 and Q216/217? I've already got some of them, physically it would fit I think. I've also got some 2N5551, 2N5401, BD139 and BD140.
It would be great if the replacement transistors were available at lcsc.com, because I have to place an order there anyway, then I don't have to buy from two dealers ... The service manual with circuit diagram can be found here: TEAC BX-500 SERVICE MANUAL Pdf Download.
I thank you in advance for your help
Best regards from Germany
Lukas
I have here a Teac BX-500 amp that was pretty much mistreated by the previous owner before i picked it up from the scrap yard. Some components are missing, there are visible burn marks on the PCB, many tracks are torn off or have been repaired provisionally, there are small holes drilled into the PCB (wtf?!), and the heat sink is bent and drilled in various places. I don't think, it's economically viable to fix this device, but I really enjoy the Design and I want to learn more about power amplifiers and that would be a good way to do so I think. Meanwhile I have listed all missing parts, for most of them I have found a replacement, but with the transistors, especially in the power amplifier, some are defective or missing, here I would need advise, which transistors can be used as replacements, because the originals aren't available anymore and I've already fallen for Fakes ...
Q111: 2SC1815 (GR)
Q112: 2SA949 (Y)
Q116: 2SD718 (O)
Q117: 2SB688 (O)
Q211: 2SC1815 (GR)
Q214: 2SC2235 (Y)
Q215: 2SA965 (Y)
Q216: 2SD718 (O)
Q217: 2SB688 (O)
Q218: 2SC2240 (GR)
Is it possible to use 2SC5200 and 2SA1943 for Q116/117 and Q216/217? I've already got some of them, physically it would fit I think. I've also got some 2N5551, 2N5401, BD139 and BD140.
It would be great if the replacement transistors were available at lcsc.com, because I have to place an order there anyway, then I don't have to buy from two dealers ... The service manual with circuit diagram can be found here: TEAC BX-500 SERVICE MANUAL Pdf Download.
I thank you in advance for your help
Best regards from Germany
Lukas
Hi Lukas,
Yes, those will work. Look for modern transistors with a similar pin-out and case style that will handle similar currents, voltages and dissipation (case style) and you should be good.
Fixing this mess should teach you quite a lot about the amplifier. Go for it!
-Chris
Yes, those will work. Look for modern transistors with a similar pin-out and case style that will handle similar currents, voltages and dissipation (case style) and you should be good.
Fixing this mess should teach you quite a lot about the amplifier. Go for it!
-Chris
2N5551, 2N5401 can replace the small signal transistors, but pins are not compatible.
The power amp section power supply voltage are +44 and -44V, BD139 and BD140 can not use in power amp section.
The power amp section power supply voltage are +44 and -44V, BD139 and BD140 can not use in power amp section.
But first you better check the transformer is ok or not.
Please prepare a Dim bulb Tester circuit first for the testing job.
Please prepare a Dim bulb Tester circuit first for the testing job.
Alright, I'll have a look for transistor equivalents and verify here with you guys.
How important is the hfe classification? I have a few 2SC1815-Y, the Amplifier Service Manual says, I need the GR version with a higher hfe. Can I try it with the low hfe ones or do I risk damaging some other parts?
I also found some 1S2473HJ and 1S2471HJ diodes in the amplifier which are broken. These look pretty standard, I found information on the internet that I can simply replace them with normal 1N4148, is that right? The transformer seems to be ok, I connected it to an isolation transformer and cut the connection to the mainboard. Then I slowly turned up the voltage, at 230V input voltage I get about 38V unloaded at both windings to ground.
I have a multimeter, an analog two channel oscilloscope (60 Mhz Hameg), a function generator and a laboratory power supply 30V/2.5A (unfortunately only one channel), so I can hopefully find and repair all errors.
I don't think that the amplifier will only work again after replacing the parts and repairing the tracks, I'm afraid there will be more broken ...
Regards
Lukas
How important is the hfe classification? I have a few 2SC1815-Y, the Amplifier Service Manual says, I need the GR version with a higher hfe. Can I try it with the low hfe ones or do I risk damaging some other parts?
I also found some 1S2473HJ and 1S2471HJ diodes in the amplifier which are broken. These look pretty standard, I found information on the internet that I can simply replace them with normal 1N4148, is that right? The transformer seems to be ok, I connected it to an isolation transformer and cut the connection to the mainboard. Then I slowly turned up the voltage, at 230V input voltage I get about 38V unloaded at both windings to ground.
I have a multimeter, an analog two channel oscilloscope (60 Mhz Hameg), a function generator and a laboratory power supply 30V/2.5A (unfortunately only one channel), so I can hopefully find and repair all errors.
I don't think that the amplifier will only work again after replacing the parts and repairing the tracks, I'm afraid there will be more broken ...
Regards
Lukas
you can use 2SC1815-Y first, a hfe range is wide, sometimes lower rank can replace higher rank. You can use 1N4148 to replace 1S2473 diode.
You repair and test the amp by each function block(like power supply, phono, pre-amp, tone control and the power amp) one by one, finally you can get your amp fixed.
Good luck!
Good luck!
That sounds like a good way to go, that's how I do it. I have now listed all the defective / missing semiconductors. With the transistors I have, as far as I could recognize it, also written down the function in the circuit and looked for a replacement type. For Q118 I am not quite sure about the function and for Q114, Q115 and Q118 I haven't found a suitable type yet, maybe one of you has an idea and can help. Here is my list:
D104 1S2473HJ 1N4148
D201 1S2473HJ 1N4148
D202 1S2473HJ 1N4148
D205 1S2471HJ 1N4148
D206 1S2471HJ 1N4148
D207 1S2471HJ 1N4148
D306 WZ150 Zener 15V 500mW 5mA
D307 WZ150 Zener 15V 500mW 5mA
Q111 2SC1815 (GR) KSC1815YTA Vbe Multiplier
Q112 2SA949 (Y) 2N5401 predriver
Q113 2SC2229 (Y) 2N5551 predriver
Q114 2SC2235 (Y) driver
Q115 2SA965 (Y) driver
Q116 2SD718 (O) 2SC5200 Output
Q117 2SB688 (O) 2SA1943 Output
Q118 2SC2240 (GR)
Thanks for the help
Lukas
PS: I took some pictures of the PCB, it looks really bad, I'll upload them right here!
D104 1S2473HJ 1N4148
D201 1S2473HJ 1N4148
D202 1S2473HJ 1N4148
D205 1S2471HJ 1N4148
D206 1S2471HJ 1N4148
D207 1S2471HJ 1N4148
D306 WZ150 Zener 15V 500mW 5mA
D307 WZ150 Zener 15V 500mW 5mA
Q111 2SC1815 (GR) KSC1815YTA Vbe Multiplier
Q112 2SA949 (Y) 2N5401 predriver
Q113 2SC2229 (Y) 2N5551 predriver
Q114 2SC2235 (Y) driver
Q115 2SA965 (Y) driver
Q116 2SD718 (O) 2SC5200 Output
Q117 2SB688 (O) 2SA1943 Output
Q118 2SC2240 (GR)
Thanks for the help
Lukas
PS: I took some pictures of the PCB, it looks really bad, I'll upload them right here!
Last edited:
Hi Lukas,
Yes, you should be alright. Once you get those things replaced (and take your time doing it), we'll see what state the amplifier is in.
I repaired one earlier in time and it turned out to be a very good performing amplifier. Better than what you might think. So it is worth repairing and too bad it was "struck by technician".
-Chris
Yes, you should be alright. Once you get those things replaced (and take your time doing it), we'll see what state the amplifier is in.
I repaired one earlier in time and it turned out to be a very good performing amplifier. Better than what you might think. So it is worth repairing and too bad it was "struck by technician".
-Chris
Are the Transistors I chose fitting replacements?
Which Transistors would be possible to use as a replacement for Q114,Q115 and Q118? For Q114 and Q115 the 2N5551 and 2N5401 would fit, but their power rating is just 0.3 instead of 0.9 Watts.
Has anyone an idea, which modern Transistor I can use? I found a few 2SB649A and 2SD669A, I guess, they would be a working replacement, but they're TO-126 instead of TO-92 so I would need to make them fit somehow ...
-Lukas
Which Transistors would be possible to use as a replacement for Q114,Q115 and Q118? For Q114 and Q115 the 2N5551 and 2N5401 would fit, but their power rating is just 0.3 instead of 0.9 Watts.
Has anyone an idea, which modern Transistor I can use? I found a few 2SB649A and 2SD669A, I guess, they would be a working replacement, but they're TO-126 instead of TO-92 so I would need to make them fit somehow ...
-Lukas
I will use the original 2SC2240 for Q118, I found some at lcsc.com.
2SB649 and 2SD669 seem to be fine for Q114 / Q115, I think I can make them fit onto the PCB ... I'll order some parts now and when they arrive, replace some components.
Regards
Lukas
2SB649 and 2SD669 seem to be fine for Q114 / Q115, I think I can make them fit onto the PCB ... I'll order some parts now and when they arrive, replace some components.
Regards
Lukas
My Spare Parts arrived today, I'll start fixing the burnt and missing traces and start to put in new components. I'll leave the Power Transistors out, so they won't burn out right away if something goes wrong. When I fixed the obvious screw-ups, I'll crank up the voltage slowly and pray, nothing explodes 😀
Regards
Lukas
Regards
Lukas
I'm back again! I put in all new components, fixed traces, made a new heatsink and slowly cranked the voltage up.
All supply voltages are present (+-44V, +-15V) and are looking god. I noticed, the protection relay won't activate, so I took a measure of the Output: on both channels there is a huge DC offset of ~ -40V, so there are obviously some things still very wrong. Atleast I know, the protection IC is fine 😀. There is a voltage drop of 6mV above the Emitter Resistors - service manual says, it should be about 25-100mV. Turning the Pots doesnt change anything. At the Test Points for Mid-Point-Potential adjustment I see the full negative supply rail, -43V. Turning the Pots here doesn't change anything either.
I find it irritating that it is exactly the same error pattern on both channels, so I suspect that it is a problem that is not found directly in the power amplifiers, but elsewhere. However, I do not know where I would have to probe. I don't really know, where to continue probing or swapping components. Maybe someone could help me a bit here?
The Service Manual can be found here: TEAC BX-500 SERVICE MANUAL Pdf Download | ManualsLib
Thank you all very much
Lukas
All supply voltages are present (+-44V, +-15V) and are looking god. I noticed, the protection relay won't activate, so I took a measure of the Output: on both channels there is a huge DC offset of ~ -40V, so there are obviously some things still very wrong. Atleast I know, the protection IC is fine 😀. There is a voltage drop of 6mV above the Emitter Resistors - service manual says, it should be about 25-100mV. Turning the Pots doesnt change anything. At the Test Points for Mid-Point-Potential adjustment I see the full negative supply rail, -43V. Turning the Pots here doesn't change anything either.
I find it irritating that it is exactly the same error pattern on both channels, so I suspect that it is a problem that is not found directly in the power amplifiers, but elsewhere. However, I do not know where I would have to probe. I don't really know, where to continue probing or swapping components. Maybe someone could help me a bit here?
The Service Manual can be found here: TEAC BX-500 SERVICE MANUAL Pdf Download | ManualsLib
Thank you all very much
Lukas
Now I'm really at my wit's end. I desoldered all transistors and tested them with the multimeter, the transistors are ok. I also checked the J-FETs, which are also fine. I also removed the protection IC for testing purposes, the DC offset does not come from a defective protection IC. Both channels still show the same error pattern. Tomorrow I will measure all voltages drawn in the service manual and write them into the schematic, and upload this here, so that you can see the nominal and actual values at all measuring points.
In the meantime, maybe someone has an idea what I could test? After I was so annoyed by my technics receiver, but now it is working, it must be possible to breathe life into the old Teac again ... 🙂
Thanks for all your help!
LG
Lukas
In the meantime, maybe someone has an idea what I could test? After I was so annoyed by my technics receiver, but now it is working, it must be possible to breathe life into the old Teac again ... 🙂
Thanks for all your help!
LG
Lukas