one of my channels is blowing a 3amp speaker fuse soon as you put one in, for a split second there is sound then pop! it's the end channel as per pic, apart from this channel all the other channels function correctly including the sub channel, any ideas?
nothing appears to be blown although the speaker cable loks to have got a little warm where it touches some resistors..
nothing appears to be blown although the speaker cable loks to have got a little warm where it touches some resistors..
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is it unusual to have blown outputs in just one channel? i havn't stripped the amp down yet but they look a similar size to those found in m50's etc.. i bought the amp as a fully working unit.... yeah right!
i'm the same marko off pg forums unless you already didn't realise! picking up those 3 ref300's this weekend
gonna be a soundstream month i think
i'm the same marko off pg forums unless you already didn't realise! picking up those 3 ref300's this weekend
gonna be a soundstream month i think
marko said:is it unusual to have blown outputs in just one channel? i havn't stripped the amp down yet but they look a similar size to those found in m50's etc.. i bought the amp as a fully working unit.... yeah right!
i'm the same marko off pg forums unless you already didn't realise! picking up those 3 ref300's this weekend
gonna be a soundstream month i think
Marko who? lol lol lol and I still say blown outputs
We can talk SS over at the other place if you like The fuses are in the supply rails to the outputs, so they blow when your Darlington's are shot. I suggest replacing both for good measure. Then check your DC offset. It should be better on the repaired channel then the rest....LMK,,, C
took the board out today to investigate and could see no signs of blown outputs, i'm guessing they could still be blown, there's 2 for each output so will need at least 2? is there a simple test i can do to to comfirm blown outputs?
gee i've got a lot of stuff to do now, a mate has given me another zpa to have a look at with suspect blown outputs and i just got a eq215x with blown earth tracks for rca's
gee i've got a lot of stuff to do now, a mate has given me another zpa to have a look at with suspect blown outputs and i just got a eq215x with blown earth tracks for rca's
Hello,
Yes, indeed you have a blown output channel as Mr. C mentioned.
The fuses are in the Negative supply rail to each channel. I'm not exactly sure why they did this but that is where they are located. The output transistors are TIP101 and TIP105's according to my schematic. (Dated 1991) This was a very common failure. There is only one P-device and one N-device per channel. (Darlington Output Transistors) Replace BOTH devices with matching date codes.
Be VERY careful when removing and replacing the main PCB! The chassis DOSE NOT have threaded mounting holes! They used sheet metal screws that can strip-out very easily if you are not careful. We lost a ton of heat sinks over the years even mounting them in production. DO NOT OVER TIGHTEN THEM! Remeber, these old amps used Mica insulators too. After your PCB installation, measure the voltage from the chassis to the output rails. You should only see a few mili-volts. It is very common to find that there many be a small piece of metal that may have come lose that will short from the Collector of one the output devices to the chassis. (heat sink)
We went to threaded heat sinks after I complained for many years before the original Reference series was released. After that...it was a no-brianer! Go figure. LOL!
Good luck to you on your repair!
pugdogs
P.S. Thanks C!
Yes, indeed you have a blown output channel as Mr. C mentioned.
The fuses are in the Negative supply rail to each channel. I'm not exactly sure why they did this but that is where they are located. The output transistors are TIP101 and TIP105's according to my schematic. (Dated 1991) This was a very common failure. There is only one P-device and one N-device per channel. (Darlington Output Transistors) Replace BOTH devices with matching date codes.
Be VERY careful when removing and replacing the main PCB! The chassis DOSE NOT have threaded mounting holes! They used sheet metal screws that can strip-out very easily if you are not careful. We lost a ton of heat sinks over the years even mounting them in production. DO NOT OVER TIGHTEN THEM! Remeber, these old amps used Mica insulators too. After your PCB installation, measure the voltage from the chassis to the output rails. You should only see a few mili-volts. It is very common to find that there many be a small piece of metal that may have come lose that will short from the Collector of one the output devices to the chassis. (heat sink)
We went to threaded heat sinks after I complained for many years before the original Reference series was released. After that...it was a no-brianer! Go figure. LOL!
Good luck to you on your repair!
pugdogs
P.S. Thanks C!
marko, to confirm blown outputs, that is if they are blowing fuses, amp is protecting as soon as power is applied etc... a simple test is to get a multimeter at set to ohms, and test beween all 3 legs (left to right, middle to right and middle to left).
the reason blown outputs blow fuses is because they internaly short out. so if ANY of the legs read really low (less than 100ohm) between them, that transistor is a gonner.
transistors dont ALWAYS short when they blow, but from my experience, most do.
another thing to note, ALWAYS replace the pair, even if just the 1 is blown, and even better is to replace all outputs in the amp, because if 1 channel blew, generally the other channel(s) have seen the same abuse.
happy fixing
h3ad
the reason blown outputs blow fuses is because they internaly short out. so if ANY of the legs read really low (less than 100ohm) between them, that transistor is a gonner.
transistors dont ALWAYS short when they blow, but from my experience, most do.
another thing to note, ALWAYS replace the pair, even if just the 1 is blown, and even better is to replace all outputs in the amp, because if 1 channel blew, generally the other channel(s) have seen the same abuse.
happy fixing
h3ad
Wait a minute...
Replace ALL output devices? Not necessary. Only replace the ones on the bad channel unless you have lots of money and time to do it all.
It's up to you. Having professionally fixed countless amps for car/home/pro audio amps over the passed 25+ years, I tend to fix what is broken. A full restoration is up to you.
pugdogs
Replace ALL output devices? Not necessary. Only replace the ones on the bad channel unless you have lots of money and time to do it all.
It's up to you. Having professionally fixed countless amps for car/home/pro audio amps over the passed 25+ years, I tend to fix what is broken. A full restoration is up to you.
pugdogs
Hello h3ad,
Sorry if I did not read your last reply correctly. It may have been the beer, the girls or something like that! LOL!
Yes, replace ALL output devices on the failing channel if you have multiple devices on that channel. You can measure from collector to emitter to find the bad device. However, the best way to check them is to lift the emitter resistors (.1 Ohm or whatever) and measure each device. I totally agree with you to replace ALL devices on the bad channel. Once a channel goes down ALL devices are BAD!
This is what we did in the service department back in the old days. We had lots of parts and wanted to fix every amp like new.
That was a long time ago but you get the picture! LOL!
Bottom line is...Don't be cheap! If you are going to fix it...fix it right!
pugdogs
Sorry if I did not read your last reply correctly. It may have been the beer, the girls or something like that! LOL!
Yes, replace ALL output devices on the failing channel if you have multiple devices on that channel. You can measure from collector to emitter to find the bad device. However, the best way to check them is to lift the emitter resistors (.1 Ohm or whatever) and measure each device. I totally agree with you to replace ALL devices on the bad channel. Once a channel goes down ALL devices are BAD!
This is what we did in the service department back in the old days. We had lots of parts and wanted to fix every amp like new.
That was a long time ago but you get the picture! LOL!
Bottom line is...Don't be cheap! If you are going to fix it...fix it right!
pugdogs
lol might have been.
but yes it a good trent to go by as i have seen many amps repaired, and blow the other channel, because the way i see it, if 1 channel has blown up, especially in stereo setups, the other channel has seen similar abuse but just managed to hold up, but will die soon after if pressured.
so when i fix amplifiers i tend to replace the outputs from other channels, even if they are "good".
but yes ALWAYS replace the pair or all of the outputs if more than 2, in a channel, becasue, say a channel has 4 outputs and 1 dies, the others have seen the same abuse, so always replace them.
anyway glad to hear you fixed your amp anyway marko.
and dont worry pugdogs, maybe beer and girls do make it hard to read lol
h3aD
but yes it a good trent to go by as i have seen many amps repaired, and blow the other channel, because the way i see it, if 1 channel has blown up, especially in stereo setups, the other channel has seen similar abuse but just managed to hold up, but will die soon after if pressured.
so when i fix amplifiers i tend to replace the outputs from other channels, even if they are "good".
but yes ALWAYS replace the pair or all of the outputs if more than 2, in a channel, becasue, say a channel has 4 outputs and 1 dies, the others have seen the same abuse, so always replace them.
anyway glad to hear you fixed your amp anyway marko.
and dont worry pugdogs, maybe beer and girls do make it hard to read lol
h3aD
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