I have been reading this forum and I've found few posts of MTX 500D amps having design flaws. I got this burned amp for free and when I open it it has visibly burned components. I don't know how bad it is but it is not a problem sense I know how to solder and I have a nice electronics shop near by.
I got few questions also. I will post pictures explaining my problem and what I need to do to fix this amp.
this capacitor was ripped off and I don't know what value it is nor what is is called. If anybody knows please post it here.
this capacitor has numbers 22J100 on it, what value is it so I can replace it.
These resistors appear burned and will probably have to replace them, with what values?
now common problem in 500D the transistors q62, q3,q61 q2 appear burned or overheated.
I know that there is few people on this board who fixed these amps before and know what components are recommended to be replaced, I will replace them all just tell me which ones.
Thanks a lot
I got few questions also. I will post pictures explaining my problem and what I need to do to fix this amp.
An externally hosted image should be here but it was not working when we last tested it.
this capacitor was ripped off and I don't know what value it is nor what is is called. If anybody knows please post it here.
An externally hosted image should be here but it was not working when we last tested it.
this capacitor has numbers 22J100 on it, what value is it so I can replace it.
An externally hosted image should be here but it was not working when we last tested it.
These resistors appear burned and will probably have to replace them, with what values?
An externally hosted image should be here but it was not working when we last tested it.
now common problem in 500D the transistors q62, q3,q61 q2 appear burned or overheated.
An externally hosted image should be here but it was not working when we last tested it.
I know that there is few people on this board who fixed these amps before and know what components are recommended to be replaced, I will replace them all just tell me which ones.
Thanks a lot
An externally hosted image should be here but it was not working when we last tested it.
If you're doing this to learn, it may be worth it but if you're repairing this because you don't have the money to buy an amp, stop now. It's likely to cost more in parts and shipping than a used, working amp.
The cap near the green inductor is probably marked .22j100 which would be a 0.22uf 100v capacitor.
The 2 burned resistors are 47.5 ohms. These only burn when the power supply FETs fail.
I don't know the value of the cap under the terminal block. If it's across the B+ and ground terminals, a 0.1uf mylar should be close enough.
The regs fail often and usually destroy op-amps in the process. If you decide to repair it, be prepared to replace all of the op-amps and the VCA (2155?). You need to check the two Zener diodes connected to the center legs of the regulator transistors. You should also change the two electrolytic capacitors connected to the first leg of the regulator transistors. At least one of the 150 ohm resistors between the regulator transistors generally fails. Check both of them.
Did the output transistors fail?
The cap near the green inductor is probably marked .22j100 which would be a 0.22uf 100v capacitor.
The 2 burned resistors are 47.5 ohms. These only burn when the power supply FETs fail.
I don't know the value of the cap under the terminal block. If it's across the B+ and ground terminals, a 0.1uf mylar should be close enough.
The regs fail often and usually destroy op-amps in the process. If you decide to repair it, be prepared to replace all of the op-amps and the VCA (2155?). You need to check the two Zener diodes connected to the center legs of the regulator transistors. You should also change the two electrolytic capacitors connected to the first leg of the regulator transistors. At least one of the 150 ohm resistors between the regulator transistors generally fails. Check both of them.
Did the output transistors fail?
Am doing this for, for hobby. I do have money, I just bought Hifonics brutus 1206D for $200 brand new and bought two speaker boxes with phoenix gold dual 10" pro subwoofers. I do have a 300zx with about $2K invested in Alpine sound system. I worked in precision power here in Phoenix until they got sold to MTX in 1999. I used to build those flat speakers. I know everything when it comes to speakers but am not that good with amps.
I don't know what failed, I got basic knowledge in electronics and I don't have osciloscope. Am willing to replace everything nesesery to get it to work but I do not whant to exed $50 in parts. I don't know how much the op-amps cost but the rest of the stuff you mentioned should not be much.
If you can help me I can test and replace everything you suggest. I got good digital volt/resistance meter
I don't know what failed, I got basic knowledge in electronics and I don't have osciloscope. Am willing to replace everything nesesery to get it to work but I do not whant to exed $50 in parts. I don't know how much the op-amps cost but the rest of the stuff you mentioned should not be much.
If you can help me I can test and replace everything you suggest. I got good digital volt/resistance meter
The op-amps are relatively inexpensive. I doubt that the parts would cost more than $50 (including shipping).
You'll need to check the output transistors near the green inductor. If you read something near 0 ohms between any of the legs of any individual transistor, the transistor has probably failed. You'd need to remove it from the board and recheck them to confirm. If the outputs have failed, the damage may be extensive and the easiest way to repair it would be to replace ~10 inexpensive transistors instead of trying to troubleshoot it.
When you replace the regulator transistors, you're going to need to repair any broken traces. It looks like the board is in pretty bad shape there. Clean it with acetone and a toothbrush (use one NOT made of clear plastic) so you can see how bad it is. Remove all of the regulator transistors (3 remain) to make it easier to clean.
Remember to check the zener diodes and the 150 ohm resistors.
You'll need to check the output transistors near the green inductor. If you read something near 0 ohms between any of the legs of any individual transistor, the transistor has probably failed. You'd need to remove it from the board and recheck them to confirm. If the outputs have failed, the damage may be extensive and the easiest way to repair it would be to replace ~10 inexpensive transistors instead of trying to troubleshoot it.
When you replace the regulator transistors, you're going to need to repair any broken traces. It looks like the board is in pretty bad shape there. Clean it with acetone and a toothbrush (use one NOT made of clear plastic) so you can see how bad it is. Remove all of the regulator transistors (3 remain) to make it easier to clean.
Remember to check the zener diodes and the 150 ohm resistors.
It's not a critical component. The amp would work without it.
I think 2 of the regulator transistors are MPSW42 and the other 2 are MPSW92.
The op-amps vary depending on when it was produced. Some used five NE5532s. Other versions had two NE5532s near the RCA jacks but the other 3 were TL072s. The 072s draw less current and may have been used to take some of the load off of the regulators.
Mini-chip?
Replace the power supply transistors, the gate resistors (47.5 ohm), the regulator parts and anything else that you find that's defective. Power it up and see if it works.
If the op-amps survived, there's no point in changing them. If you have to change them, you'll need a good iron, good desoldering braid and/or a good desoldering pump... and a lot of patience. If you aren't patient and you destroy the vias in the board, it may be VERY difficult to troubleshoot/repair from that point.
If the op-amps survived, there's no point in changing them. If you have to change them, you'll need a good iron, good desoldering braid and/or a good desoldering pump... and a lot of patience. If you aren't patient and you destroy the vias in the board, it may be VERY difficult to troubleshoot/repair from that point.
I have a very good desoldering tools, I have been pulling epromms from automotive computers and these op amps are very easy for me.
What are the power transistors in this amp? Do you know the designations looking at the picture above?
Should I increase the resistance and wattage of the gate resistors to make them cope better with heat?
What are the power transistors in this amp? Do you know the designations looking at the picture above?
Should I increase the resistance and wattage of the gate resistors to make them cope better with heat?
If you can 'easily' change the op-amps and are sure you won't damage the board, change them. You may want to pull them before powering up the amp in case any are shorted or otherwise pulling excessive current. After getting the regulators working properly (not before), you can install the new op-amps.
The power transistors are FET101-FET104 and FET202-FET204. 201-204 are defective unless someone has replaced them. You need to check the audio output FETs (101-104).
Don't change the value of the gate resistors. They failed because the FETs failed. They are sacrificial. If they don't fail, it could cause the driver transformer (T201) to fail.
You may want to increase the value of the 150 ohm resistors between the regulators (use 390 ohm, 1/2 watt). It will help the regulators run slightly cooler. Mount them between the board and the sink instead of between the regulators.
The power transistors are FET101-FET104 and FET202-FET204. 201-204 are defective unless someone has replaced them. You need to check the audio output FETs (101-104).
Don't change the value of the gate resistors. They failed because the FETs failed. They are sacrificial. If they don't fail, it could cause the driver transformer (T201) to fail.
You may want to increase the value of the 150 ohm resistors between the regulators (use 390 ohm, 1/2 watt). It will help the regulators run slightly cooler. Mount them between the board and the sink instead of between the regulators.
I pulled the two board resistors R228 and R229 and they both have failed (no resistance readings, open) so that means the driver transformer is safe T201.
What is the cheapest and common FET that will work in my aplication? When I got to electronic store I have to tell them exacly the FET I need or they don't know what to tell me.
What is the cheapest and common FET that will work in my aplication? When I got to electronic store I have to tell them exacly the FET I need or they don't know what to tell me.
It's not a 'guarantee' that the driver transformer didn't fail but it's more than likely that it survived.
Unless you have a really well stocked local electronics outlet, they won't have what you need. Whatever you do, do NOT buy NTE or similar generic replacements.
For the power supply, if the exact replacements are not available, use IRF3205s or IRFZ48s.
Mouser.com should have everything that you'll need.
Did you ever determine if the outputs (FET101-104) survived. If they did, you do not want to use replacements. Even if they have the same exact part number, there's no guarantee that they'll work properly. These amps are very sensitive to changes in the audio section (especially the output transistors).
Unless you have a really well stocked local electronics outlet, they won't have what you need. Whatever you do, do NOT buy NTE or similar generic replacements.
For the power supply, if the exact replacements are not available, use IRF3205s or IRFZ48s.
Mouser.com should have everything that you'll need.
Did you ever determine if the outputs (FET101-104) survived. If they did, you do not want to use replacements. Even if they have the same exact part number, there's no guarantee that they'll work properly. These amps are very sensitive to changes in the audio section (especially the output transistors).
Generally, the the FETs fail, they short between legs.
For output and power supply FETs, if you ever read anything other than an open connection between the first leg and the other two legs, the FET is defective.
If you read 0 ohms between legs 2 and 3, the FET is defective.
For a more extensive test, read the section labeled 'Checking Field Effect Transistors' on the following page. You must remove the FET from the board for testing.
http://www.bcae1.com/ampfail.htm
For output and power supply FETs, if you ever read anything other than an open connection between the first leg and the other two legs, the FET is defective.
If you read 0 ohms between legs 2 and 3, the FET is defective.
For a more extensive test, read the section labeled 'Checking Field Effect Transistors' on the following page. You must remove the FET from the board for testing.
http://www.bcae1.com/ampfail.htm
Perry Babin said:
According to their website the IRF3205 is absolete, and IRFZ48 is available. I will go down to the electronic store and see if they have them. If the electronic store only have NTE then I shall buy the 75339Ps from mouser.com,
Did you say when power regs FETs 201 ~ 204 fail the op amps go out too?
am reading this thread:
http://www.diyaudio.com/forums/showthread.php?threadid=111837
The IRF3205ZPBF is still active and available. Digikey has 11,000+ of them. The Z48 will do the job if you want to buy everything from mouser.
201-204 are power transistors that drive the transformer. They have nothing to do with the regulators (MPSW42/92) near the 150 ohm resistors.
The op-amps fail when the regulator transistors fail and short. This applies rail voltage to the preamp ICs. Instead of getting 36v (±18, the max they're rated for), they get 50-60v (possibly more if both positive and negative regs fail).
201-204 are power transistors that drive the transformer. They have nothing to do with the regulators (MPSW42/92) near the 150 ohm resistors.
The op-amps fail when the regulator transistors fail and short. This applies rail voltage to the preamp ICs. Instead of getting 36v (±18, the max they're rated for), they get 50-60v (possibly more if both positive and negative regs fail).
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