dogwan
Dogwan
I have a pair of matching vintage Altec subs with built-in amps. No service manual or schematic anywhere to be found (I've looked for years). The amp section is using 2sa1302 and 2sc3281.
Even though I don't have a service manual I figured a straight re-cap should not be a problem. Pretty straight forward, but the subs are different revisions and I'm having a problem with one.
Did the full recap and the earlier one works great. The later one powered up fine but no sound. After about 60 seconds a 1Ω resistor flamed out and I shut it down really fast.
Here's the thing... on the latter one the silk screen for a cap in series with the flamed resistor is the opposite polarity of the silk screen on the earlier working amp?
As follows:
Working amp....
+(47uf cap)- ---> 1Ωr ---> Collector on PNP
-(47uf cap)+ ---> 1Ωr ---> Collector on NPN
Problem amp
-(47uf cap)+ ---> 1Ωr ---> Collector on PNP (this is the one that burned up)
-(47uf cap)+ ---> 1Ωr ---> Collector on NPN
Does this look right? I noticed when I had the caps out that the polarity marking was different, but there were a couple other subtle differences in the boards so I trusted the silk screening. As luck would have it this one the cap that literally fell out when I unsoldered before I could double check the polarity against the silk screen. The board is definitely lower quality than the earlier one. Also, on the daughter boards the caps didn't even have polarity markings. I'm guessing some penny pinching went on later in the run.
I've run a continuity and diode test on the associated transistors and output devices and they measure the same as the working amp (although I did this in circuit). Should I replace the burnt resistor and reverse the cap in question (with a replacement of course) and give it a try?
Also, if that cap was reversed could it have caused DC on the output and caused the output relay to prevent output to the driver?
Too late to get pictures up, but can tomorrow night if needed. Thanks in advance.
Even though I don't have a service manual I figured a straight re-cap should not be a problem. Pretty straight forward, but the subs are different revisions and I'm having a problem with one.
Did the full recap and the earlier one works great. The later one powered up fine but no sound. After about 60 seconds a 1Ω resistor flamed out and I shut it down really fast.
Here's the thing... on the latter one the silk screen for a cap in series with the flamed resistor is the opposite polarity of the silk screen on the earlier working amp?
As follows:
Working amp....
+(47uf cap)- ---> 1Ωr ---> Collector on PNP
-(47uf cap)+ ---> 1Ωr ---> Collector on NPN
Problem amp
-(47uf cap)+ ---> 1Ωr ---> Collector on PNP (this is the one that burned up)
-(47uf cap)+ ---> 1Ωr ---> Collector on NPN
Does this look right? I noticed when I had the caps out that the polarity marking was different, but there were a couple other subtle differences in the boards so I trusted the silk screening. As luck would have it this one the cap that literally fell out when I unsoldered before I could double check the polarity against the silk screen. The board is definitely lower quality than the earlier one. Also, on the daughter boards the caps didn't even have polarity markings. I'm guessing some penny pinching went on later in the run.
I've run a continuity and diode test on the associated transistors and output devices and they measure the same as the working amp (although I did this in circuit). Should I replace the burnt resistor and reverse the cap in question (with a replacement of course) and give it a try?
Also, if that cap was reversed could it have caused DC on the output and caused the output relay to prevent output to the driver?
Too late to get pictures up, but can tomorrow night if needed. Thanks in advance.
Also, when in doubt and you cannot find the (correct) answer, use a Bi-Polar (non-polarized) cap.