I did that yesterday after cooking the fuse.
It was well over the 31 v it should be. In the 70's I believe and I found both AC and DC in the path.
I must have a few hundred brand new caps sorted and stashed in bead boxes so I could replace every cap in this thing and not even notice them gone but...
It will be C004 and C005....possibly C008 I need to replace if I am not mistaken?
I know power caps are always tremendous values and unfortunately, the largest I have left after a few recent projects are 200v 1000 uF. Fortunately at those meager voltages, they are cheap to buy. I can Ebay them for 10 bucks a pair or airmail from China for about $4 and some change.
But just as importantly, does anyone know of a good cleaner I can use?
I'm willing to get in there with some toothbrushes and salvage this Rolls-Royce of solid state
In the 70s sounds like you put the probes of the DMM across both voltage rails, measure with respect to ground (hold black lead to casing or outside of RCA connector). In a normally working amp, you would get -31 V on the negative rail and + 31 V on the positive rail with respect to ground.
Please post the precise DC and AC voltage readings of both power rails.
That you may still do if the problems with the amp are small and fixed. Chances are other components like transistors have failed too.
Yes, these are the smoothing caps for the power amp stage. If readings indeed show excessive AC voltage, it's indeed likely that C004 and C005 have dried out.
Do yourself a favour and buy good stuff from reputable dealers. You don't want to get second grade stuff that makes you need to do this again in a couple of years. Quality brands should last for over another decade or two...
Jitter I appreciate all the help but please don't assume I'm ignorant and buy junk. I was very offended by that. I have plenty of experience with preamp designing and building. This is however my first knee deep experience in repairing a power amp.
Buying components through eBay is high risk when it comes to counterfeit or second grade components. The only way of being sure about good quality is through reputable vendors (good) or authorized resellers (better). The company I work for has fallen victim to counterfeit or bad quality components on more than one occasion. Since the decision was made to buy only from companies such as Avnet or Arrow have we been spared the enormous trouble that counterfeits gave us in the past.
Please accept my apologies, offense was not intended.
Please accept my apologies, offense was not intended.
Thanks for the apology.
I have a select few suppliers I trust on Ebay for my components. I'll order a few small parts a few times and if they prove reliable, continue purchasing from them. Generally, all my purchases go to Tayda so Jackc caps are about as cheap as I'll buy. I also make a lot of quantity purchases through Mouser. I'm also almost always doing preamp work though so a device definitely has to be pretty ratty to perform poorly or fail in preamp operating conditions.
On the other hand, I put plenty of caps under stress in the numerous crossovers I build and routinely experiment with. I've had easily a dozen caps explode as loud as firecrackers lol
On ebay for 11 bucks I found Nover audio grade caps from a Chinese seller. A decade ago on Ebay after getting burnt a few times, I believe I was the first person to actually rate the ITEM in feedback rather than that brainwashing trend of "AAAAA++ SELLER! Great transaction!" which many people still so foolishly do today.
I will dig through dozens of pages of feedback looking for product reviews and in fact, recently had a 14 day suspension because a few sellers complained that I told the truth about the garbage they sent me even though they refunded me lol.
If you sell me junk, paying me off won't turn me into a liar.
These reviewers are nowhere near as specific as I am and prefer to find but everyone seems happy with the quality from him/her.
2pcs x 6800uF 50V Nover Audio Grade Power 85°C Capacitor Negative Black | eBay
I am assuming these will be substantially higher quality that the Jakec. I have an appreciation for vintage equipment so $11 to repair this unit is a steal. I still need to find a suitable cleaner I can toothbrush all the PCB's with then something to spray it with as a protective. I was really unhappy when I saw the corrosion that occurred from no longer using it because it was pretty clean before I shelved it.
I checked the rail voltages in respect to ground and all are 29.1 volts.
I also noticed a power resistor that doesn't look completely cooked but it is fairly brown in the middle and it's not from corrosion. The other one has a slightly tanned center. I'll meter those and prepare to replace them in upcoming weeks along with the capacitors.
I am unfortunately the cliche poor college kid with $1.57 in my bank account for the next 2 weeks lol.
I hit the corrosion with a toothbrush and some elbow grease takes it off pretty well. I am assuming 90% alcohol is safe but I also have a reverse osmosis filtration system in the house so it should be safe to use as well since it contains no minerals of conductance. I've meter tested it a variety of ways and it is definitely inert.
I also noticed a power resistor that doesn't look completely cooked but it is fairly brown in the middle and it's not from corrosion. The other one has a slightly tanned center. I'll meter those and prepare to replace them in upcoming weeks along with the capacitors.
I am unfortunately the cliche poor college kid with $1.57 in my bank account for the next 2 weeks lol.
I hit the corrosion with a toothbrush and some elbow grease takes it off pretty well. I am assuming 90% alcohol is safe but I also have a reverse osmosis filtration system in the house so it should be safe to use as well since it contains no minerals of conductance. I've meter tested it a variety of ways and it is definitely inert.
I assume this is DC voltage. Two questions:
- is the negative rail voltage also positive?
- what are the AC values?
If you mean the emitter-resistors (R853..R856) of the output transistors:
If this is the result of overheating and blowing, then the power transistors might be blown too. These resistors should measure 0.47 Ohms (subtract the lead resistance from you DMM from the measured value). If they're way higher or open, they're blown.
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The Nover capacitors are decent enough if genuine. One thing to watch out for - they will likely be physically smaller than the originals - capacitor technology has improved substantially since 1973
Also good are Panasonic's TSHA and TSUP series. In fact Panasonic capacitors in general are a good brand, and available for very reasonable prices.
Also good are Panasonic's TSHA and TSUP series. In fact Panasonic capacitors in general are a good brand, and available for very reasonable prices.
I'll go with a major branding from the most affordable source.
I kinda had to laugh at your "if genuine".
They're capacitors, not designer watches. While counterfeiting does occur, nobody is going to counterfeit 20 general Nover audio grade capacitors then sell them on Ebay at $12 a set lol
They're going to counterfeit at the very least in the hundreds and it's going to be something rare and highly sought after in the A/V community. No offense but the concern that just because it's on Ebay there might be something wrong with it does not relate to my experience with thousands of purchases.
I again felt as though you were talking down to me without knowing me but, I think maybe you are a little arrogant and paranoid.
I kinda had to laugh at your "if genuine".
They're capacitors, not designer watches. While counterfeiting does occur, nobody is going to counterfeit 20 general Nover audio grade capacitors then sell them on Ebay at $12 a set lol
They're going to counterfeit at the very least in the hundreds and it's going to be something rare and highly sought after in the A/V community. No offense but the concern that just because it's on Ebay there might be something wrong with it does not relate to my experience with thousands of purchases.
I again felt as though you were talking down to me without knowing me but, I think maybe you are a little arrogant and paranoid.
Unfortunately I must admit I like most people outside these close knit internet communities do not do well on this sites forum when we come in from the outside. I have helped and continue to help many people but there is most definitely a general tone from the regs on this site where sooner or later, that help comes at the price of being talked down to as a child simply because you lack the knowledge someone else has.
It's just one aspect of our lives though and the attitude here is often that those asking for help are doing so out of incompetence rather than ignorance.
I admit, I am ignorant on the subject but, I'm neither a child nor an idiot that needs warnings of the ways of the world lol. It should go without saying that I'm not going to buy junk from brand X. It should also go without saying that counterfeit parts will be exclusive to very expensive brands or rare vintage parts, not a $12 set of capacitors a radio shop has 40 of for sale.
I think some people make these condescending statements intentionally and others are trying so hard to be helpful, they don't realize that some comments require the recipient to be a 14 year old kid for the statements to be sensible.
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