I have a soundstream reference 300 that is not functioning properly. I opened it up and see a pair of charred ceramic resistors. They are down at the edge right near the power/speaker connections. They are both identical. Unfortunately they are charred to the point where I cannot read the color bands. They are labelled as R121 and R122. First band is definitely orange There is also a Brown and a Gray (in that order) I cannot tell if there are bands between the orange and brown or the brown and gray. The last band is definitely gold. So if I assume there are no bands in the charred area that I cannot see that would mean this is a 380 ohm 5% tolerance. They both measure right at 400 ohm with my cheapo autorange radio shack dmm. Does that sound right?
I do not see any other burnt or charred components.
Here is a pic:
The amp would play normally then pretty much randomly it would give a slight pop and have no output, it would come back on in as little as a few minutes. It was not being driven hard, it was running a single 4 ohm 12, and it would cycle on and off even at low volumes, not a heat protection thing as the amp was still cool to the touch.
Thanks for the help!
I do not see any other burnt or charred components.
Here is a pic:
An externally hosted image should be here but it was not working when we last tested it.
The amp would play normally then pretty much randomly it would give a slight pop and have no output, it would come back on in as little as a few minutes. It was not being driven hard, it was running a single 4 ohm 12, and it would cycle on and off even at low volumes, not a heat protection thing as the amp was still cool to the touch.
Thanks for the help!
Can't see the pic but I'd say your right.
Being a 5% tells me it's a carbon film/core.
as such it may have cracked internally, so when it warms up it either goes high resistance or open.
That would explain the clicks etc.
Edit; ok can see pic, problem with connection my end.
They aren't ceramic, they are caron film resistors.
Orange-grey-brown is 380 ohm.
When you replace them i would space them of the board a touch (2mm) to help protect the board from damadge.
Being a 5% tells me it's a carbon film/core.
as such it may have cracked internally, so when it warms up it either goes high resistance or open.
That would explain the clicks etc.
Edit; ok can see pic, problem with connection my end.
They aren't ceramic, they are caron film resistors.
Orange-grey-brown is 380 ohm.
When you replace them i would space them of the board a touch (2mm) to help protect the board from damadge.
Finding resistors
You can try Parts Express.com, they carry two or three types of resistors in their catalog. Look under the heading Electronis parts. Good luck, I have an old Soundstream 3.0 amp sitting in the garage, nice amps. Rob
You can try Parts Express.com, they carry two or three types of resistors in their catalog. Look under the heading Electronis parts. Good luck, I have an old Soundstream 3.0 amp sitting in the garage, nice amps. Rob
I'd recommend digikey.com for parts.
I don't think that these are the problem. This type of resistor often looks just like the ones you have if they are run at or near rated power. The outer finish gets discolored but the resistors are typically fine. The type of problem that you described is not likely to have any physical signs (except for bad solder connections).
If you still want to replace them, measure the resistors and find some of comparable size. From the photo, I'd say that they are 1-2 watt resistors. On digikey's site search for 390w (closest to 380 ohms in most resistor lines). Select metal film or metal oxide film and find the resistor that is the best match for the physical size of your resistors.
I don't think that these are the problem. This type of resistor often looks just like the ones you have if they are run at or near rated power. The outer finish gets discolored but the resistors are typically fine. The type of problem that you described is not likely to have any physical signs (except for bad solder connections).
If you still want to replace them, measure the resistors and find some of comparable size. From the photo, I'd say that they are 1-2 watt resistors. On digikey's site search for 390w (closest to 380 ohms in most resistor lines). Select metal film or metal oxide film and find the resistor that is the best match for the physical size of your resistors.
I thought these were carbon film? Are metal oxide the same? Will changing type make a difference?
I am hoping to get the resistors at a place where I can also order a cheapo DMM (I will use the DMM as my payment for fixing the amp).
I am looking for the cheapest true RMS dmm I can find too, I have found some for $40-$60
I am hoping to get the resistors at a place where I can also order a cheapo DMM (I will use the DMM as my payment for fixing the amp).
I am looking for the cheapest true RMS dmm I can find too, I have found some for $40-$60
The type of resistor isn't really important as long as the value and power handling are correct.
Don't buy a cheap meter. I'd much rather see someone buy a used Fluke than a new anything else. I know lots of techs and none of them use anything other than Fluke handheld/portable meters. They get used daily and VERY rarely have problems. I have a Fluke 27 that I purchased new in 1986 or 1987 and it's still accurate and works perfectly. You can ask for feedback from others here for meters but I'd recommend Fluke.
For repair work, if you don't have to have true RMS capability, I'd recommend trying to find a used Fluke 11. It's the best handheld meter I've ever used for repair work. When switched on, it defaults to diode check or DC volts (precisely what you need for repairing DC powered equipment). When testing semiconductors or continuity on diode check, it beeps instantly. Most other meters have an annoying short (1/2 second) delay. It doesn't sound like much but it makes a difference. If you have it on diode check and you need to check voltage, you don't need to change settings. The only time you need to change to voltage is when measuring voltage on sensitive circuits (the DC biasing of the diode check function will shift the voltage of sensitive circuits).
Don't buy a cheap meter. I'd much rather see someone buy a used Fluke than a new anything else. I know lots of techs and none of them use anything other than Fluke handheld/portable meters. They get used daily and VERY rarely have problems. I have a Fluke 27 that I purchased new in 1986 or 1987 and it's still accurate and works perfectly. You can ask for feedback from others here for meters but I'd recommend Fluke.
For repair work, if you don't have to have true RMS capability, I'd recommend trying to find a used Fluke 11. It's the best handheld meter I've ever used for repair work. When switched on, it defaults to diode check or DC volts (precisely what you need for repairing DC powered equipment). When testing semiconductors or continuity on diode check, it beeps instantly. Most other meters have an annoying short (1/2 second) delay. It doesn't sound like much but it makes a difference. If you have it on diode check and you need to check voltage, you don't need to change settings. The only time you need to change to voltage is when measuring voltage on sensitive circuits (the DC biasing of the diode check function will shift the voltage of sensitive circuits).
My usage will be pretty simple, continuity checks, finding switched power, and possibly setting gains (where the true rms comes into play).
not sure how much repair I will be doing, this is my first foray into that field.
Also might use it for minor projects as I find interest (minor HT speaker building, etc)
not sure how much repair I will be doing, this is my first foray into that field.
Also might use it for minor projects as I find interest (minor HT speaker building, etc)
Some True RMS meters are only accurate for a narrow range of frequencies. Many have a range of only ~500Hz. If you need it for audio and want it to be accurate for the entire audible spectrum, find the spec sheet on it to be sure that it responds accurately up to ~20kHz before buying it.
A reference 300 came into the shop today. It had several problems. Your amp may have similar problems.
The resistors are 390 ohms. The second band is white.
The solder connections on the resistors were badly oxidized. If yours are also oxidized, simply desoldering then resoldering them may solve your problem.
The amp also had several intermittant connections on the vertical driver boards. Desolder and then resolder those also if yours shows signs of cracked solder joints (where the driver board connects to the main board).
The resistors are 390 ohms. The second band is white.
The solder connections on the resistors were badly oxidized. If yours are also oxidized, simply desoldering then resoldering them may solve your problem.
The amp also had several intermittant connections on the vertical driver boards. Desolder and then resolder those also if yours shows signs of cracked solder joints (where the driver board connects to the main board).
Thank you so much! Do you know if 1 watt is enough for the resistors or should I go 2 watt (I did find a 2 watt 390 ohm)
If you need a replacement (possible but unlikely), I'd suggest a CWC-390 (from digikey). It's the same size as the resistors in the amp I have here but they are rated at 3.75 watts.
The resistors are dropping 22 volts. That's 1.25 watts so a 2 watt should be fine (that's what soundstream used). A 1 watt would not survive. The resistor I recommended is overkill but it will fit and it doesn't cost much more than a standard 2 watt.
The 390W-2 looks like an exact replacement for the OEM part.
The resistors are dropping 22 volts. That's 1.25 watts so a 2 watt should be fine (that's what soundstream used). A 1 watt would not survive. The resistor I recommended is overkill but it will fit and it doesn't cost much more than a standard 2 watt.
The 390W-2 looks like an exact replacement for the OEM part.
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