New to posting, long time lurker.
I got a new Pioneer C-91 preamplifier from eBay recently at a good price for repair and it was described as having a low level hum.
Quick review and verification that the unit works properly with a hum in the background. Initial inspection shows the quite complex power supply has sign of heat and that the caps around them are out of spec. I removed a few and measured them with an trusted Sencore LC-102 to show less than half it's nominal values and shows as bad.
This pre is considered to be very good for the era. It has a lot of Nichicon Muse caps in the audio portion, rare in this type of mass produced equipment.
At the moment I am concentrated in the power supply in the main AF board. If need be will address further after this first round of repairs.
Here are the questions.
The power supply uses 2 different type of electrolytic and I am having a hard time matching them to the very extensive line of Nichicon caps.
I posted pictures of the difficult caps.
Any help would be appreciated.
Pictures show a cap of 470/50V with an extra lead at the top. Seen them many times but not common. Any ideas why this is needed?
The brown 330/50V cap is significantly bigger than same values in the green line. This one is described as a CEXA type by Pioneer. What family would this one correspond to?
Thanks
I got a new Pioneer C-91 preamplifier from eBay recently at a good price for repair and it was described as having a low level hum.
Quick review and verification that the unit works properly with a hum in the background. Initial inspection shows the quite complex power supply has sign of heat and that the caps around them are out of spec. I removed a few and measured them with an trusted Sencore LC-102 to show less than half it's nominal values and shows as bad.
This pre is considered to be very good for the era. It has a lot of Nichicon Muse caps in the audio portion, rare in this type of mass produced equipment.
At the moment I am concentrated in the power supply in the main AF board. If need be will address further after this first round of repairs.
Here are the questions.
The power supply uses 2 different type of electrolytic and I am having a hard time matching them to the very extensive line of Nichicon caps.
I posted pictures of the difficult caps.
Any help would be appreciated.
Pictures show a cap of 470/50V with an extra lead at the top. Seen them many times but not common. Any ideas why this is needed?
The brown 330/50V cap is significantly bigger than same values in the green line. This one is described as a CEXA type by Pioneer. What family would this one correspond to?
Thanks
Attachments
![IMG_4089[1].jpg](/community/data/attachments/556/556128-eab2ef28ca2aecbe9ed6fd14dbfcaf25.jpg?hash=6rLvKMoq7L)
![IMG_4090[1].jpg](/community/data/attachments/556/556145-7a5e5e8f457bca72c049294238d8bcda.jpg?hash=el5ej0V7yn)
![IMG_4091[1].jpg](/community/data/attachments/556/556161-d691468dbf4e40e0cfd04c7659a64c0a.jpg?hash=1pFGjb9OQO)
Is the lead coming from the top isolated from the the others?
if they are i can only assume that it provides some sort of shielding.
if the top lead is not isolated then is it a dual ecap? in other words you measure capacitance from each lead to the lead coming from the top.
I have not seen these in a ecap's in mfg's catalogues before, so I assume that they are specially made for Pioneer.
Do you have a schematic of this model so i can see where they are used in the circuit?
if they are i can only assume that it provides some sort of shielding.
if the top lead is not isolated then is it a dual ecap? in other words you measure capacitance from each lead to the lead coming from the top.
I have not seen these in a ecap's in mfg's catalogues before, so I assume that they are specially made for Pioneer.
Do you have a schematic of this model so i can see where they are used in the circuit?
A-91D.pdf
They don't seem to be drawn different but I think the top lead is connected to the capacitors negative terminal on the pcb see caps C401~4?
c-90a.html used the same caps
heres a translation
"I connected an aluminum case to the cathode of the aluminum electrolysis condenser more surely, and parts of the sound quality priority including the new development seal dead capacitor which controlled the bursting in of the noise from the outside, the jumping out of the noise from the condenser by a powerful shield were used."
regards
james
They don't seem to be drawn different but I think the top lead is connected to the capacitors negative terminal on the pcb see caps C401~4?
c-90a.html used the same caps
heres a translation
"I connected an aluminum case to the cathode of the aluminum electrolysis condenser more surely, and parts of the sound quality priority including the new development seal dead capacitor which controlled the bursting in of the noise from the outside, the jumping out of the noise from the condenser by a powerful shield were used."
regards
james
Hello James,
Thanks for both links. In effect the extra lead is connected to the negative side or isolated. Have seen both cases. All my extra research has found that they added it for physical support. Apparently they did not want to repeat the glue fiasco with the M-90 amps and the glue that becomes somewhat conductive and corrosive. On the other hand they are not big at all and wonder why the need to secure them extra.
The curios part is that all these capacitors are used in a power supply setting, with the copper oxygen free lead unit (brown case AVF) used as filter. Three levels of filtering with 3 different kind of electrolytic capacitors is interesting at this level.
I was able to find some more info at the Nippon Chemi-Con Japanese site, but nobody carries some of these in the USA.
And finally, the 3rd legged cap I have never seen in in any catalog. I am replacing them with the best quality Nichicon caps I found at Mouser.
I got some KA Audio grade for the final ones. I will post results.
Thanks for both links. In effect the extra lead is connected to the negative side or isolated. Have seen both cases. All my extra research has found that they added it for physical support. Apparently they did not want to repeat the glue fiasco with the M-90 amps and the glue that becomes somewhat conductive and corrosive. On the other hand they are not big at all and wonder why the need to secure them extra.
The curios part is that all these capacitors are used in a power supply setting, with the copper oxygen free lead unit (brown case AVF) used as filter. Three levels of filtering with 3 different kind of electrolytic capacitors is interesting at this level.
I was able to find some more info at the Nippon Chemi-Con Japanese site, but nobody carries some of these in the USA.
And finally, the 3rd legged cap I have never seen in in any catalog. I am replacing them with the best quality Nichicon caps I found at Mouser.
I got some KA Audio grade for the final ones. I will post results.
After some long research and looking at cost and availability I placed an order with Mouser for the four sets of capacitors used in the regulated power supply of the C-91. I ended up using a combination of Nichicon power supply caps, some Panasonic FM and a Muse Nichicon also.
The goal was to be as consistent with a restoration vs a repair. The results are that the pre-amp is very quiet and the hum disappeared. Most other caps looked OK and measured correctly. Only some in the PS were grossly out of spec.
It is always a challenge to choose the right cap. Too many options and too many good brands.
The goal was to be as consistent with a restoration vs a repair. The results are that the pre-amp is very quiet and the hum disappeared. Most other caps looked OK and measured correctly. Only some in the PS were grossly out of spec.
It is always a challenge to choose the right cap. Too many options and too many good brands.
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