Hi, I’m trying to repair a Vitus RI-100 integrated amplifier. This amplifier has socketed input modules, one per channel, please see picture. One channel has high DC on the output. It starts low, when initially powered on and then quickly rises to over 1V DC as it warms up. If I swap these modules between channels, DC problem also swaps. So I have it narrowed down to the module.
The amplifier works and produces sound, but I’m assuming that one or more of the transistor is partially leaking DC. And over 1V DC is extremely high.
The little SMD transistors are labeled RS and TS. I cannot seem to find what these SMD codes correspond to as far as actual transistor part numbers.
Any help would be greatly appreciated.
The amplifier works and produces sound, but I’m assuming that one or more of the transistor is partially leaking DC. And over 1V DC is extremely high.
The little SMD transistors are labeled RS and TS. I cannot seem to find what these SMD codes correspond to as far as actual transistor part numbers.
Any help would be greatly appreciated.
As always, a stereo amplifier can be troubleshot and repaired by comparing the good channel with the bad one.
Resistance, transistor junctions, voltage readings, all easily determined, to find the failing part.
Resistance, transistor junctions, voltage readings, all easily determined, to find the failing part.
First thing I did was to resolder every single part. No change. All resistors show fine at least on a simple Fluke ohmmeter. I also replaced the 4 ceramic capacitors. Still no change. The way the amp is assembled and the location of the modules, checking and comparing voltages between channels is very difficult. It would be quicker for me to just replace the parts if I could identify the small transistors. The 4 larger transistors are SMD versions of MPSA92/42 and the 2 diodes are 4.7V Zener.
Next check all the transistors with the diode function of the DVM.
Then touch each during operation with an insulated tool, and watch for any change.
The problem is more DC drift than leakage.
Do you know for sure that the offset has recently happened, and is not a factory defect?
Then touch each during operation with an insulated tool, and watch for any change.
The problem is more DC drift than leakage.
Do you know for sure that the offset has recently happened, and is not a factory defect?
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Repairing this for a client, according to him, the amplifier when purchased worked fine. Initial complaint was that the amplifier goes into DC protection. It’s not going into DC protection in my possession, but I also have not kept it on for a long period of time. The voltage rises very fast when turned on and continues to rise. It got well over 1V DC after several minutes of on time. Not sure what exact voltage triggers DC protection.
If I swap the modules between channels, then the other channel shows rising DC. So the rest of the amplifier seems to be fine in my opinion. This amp is about 10 years old, or so.
At this point, I would just prefer to order all new parts from DigiKey and rebuild the entire module. Have everything figured out except for the RS/TS marked transistors. From what I found while Googling, it’s possible that these SMD codes correspond to 2SA1514K and 2SC3906K pairs.
Aside from DC, the amplifier works and produces clean sound in both channels. I also cleaned the PCB with acetone in hopes that something might be shorting, etc. But no change. I believe the PCB is a multi layer PCB, I hope it’s not a failing or cracked internal track somewhere.
If I swap the modules between channels, then the other channel shows rising DC. So the rest of the amplifier seems to be fine in my opinion. This amp is about 10 years old, or so.
At this point, I would just prefer to order all new parts from DigiKey and rebuild the entire module. Have everything figured out except for the RS/TS marked transistors. From what I found while Googling, it’s possible that these SMD codes correspond to 2SA1514K and 2SC3906K pairs.
Aside from DC, the amplifier works and produces clean sound in both channels. I also cleaned the PCB with acetone in hopes that something might be shorting, etc. But no change. I believe the PCB is a multi layer PCB, I hope it’s not a failing or cracked internal track somewhere.
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Oh, and I did check each transistor with the DVM function and they all look good and match the other channel.
Then how do you blame the transistors?
If you swap the modules, the other has a fault?
Check the power supply regulation, it is possible there is a regulator on the module also. See that first.
If you swap the modules, the other has a fault?
Check the power supply regulation, it is possible there is a regulator on the module also. See that first.
DC on the output follows the module. If I put the bad input module in the left channel, I get DC on the output of the left channel. If I put the bad module in the right channel, I get DC on the output of the right channel. Which means that the rest of the amplifier is working correctly and the fault lies somewhere in the bad module. This much is certain.
I resoldered all of the parts. As you can see in the picture, there’s really not much to it. Even though the transistors check okay on the DVM setting of the ohmmeter, it’s not a guarantee and one or more could be drifting or leaking DC while powered on. I suppose same is true for the resistors, it may test ok with the ohmmeter, but could be partially failing while powered on.
If anyone has any info on the SMD codes, I would greatly appreciate that information. Even if I go through all of the troubleshooting and find the exact transistor which is failing, I will still need to decipher the SMD code in order to purchase a replacement.
I resoldered all of the parts. As you can see in the picture, there’s really not much to it. Even though the transistors check okay on the DVM setting of the ohmmeter, it’s not a guarantee and one or more could be drifting or leaking DC while powered on. I suppose same is true for the resistors, it may test ok with the ohmmeter, but could be partially failing while powered on.
If anyone has any info on the SMD codes, I would greatly appreciate that information. Even if I go through all of the troubleshooting and find the exact transistor which is failing, I will still need to decipher the SMD code in order to purchase a replacement.
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Thank you! I’ve used that site to get the 2SA1514K and 2SC3906K pair as a possible match. But how can one be sure if that’s the transistors used without the schematic? There’s a handful of transistors that are labeled TS and RS and match in size.
You can't be sure, but i'd be 90% certain. Those Rohm transistors look like good high voltage and low noise transistors in a small package. They were probably guilding the lily a bit...
Indeed, I would think that this amplifier would have service info available and/or manufacturer support.
For an amplifier that originally cost $18,000 US.