I have a Hafler TA-1600 with classic “no bass or midrange” syndrome apparently attributable to failed surface mounts capacitors. Both channels afflicted. I am not competent or set up with proper tools yo remove and replace the caps so I contacted a local shop specializing in audiophile and pro gear. They said complete recap will exceed $350.
I want to go forward with repair because I just hate seeing the chassis, heat sink, transformer and lateral MOSFETs go to waste. What advice does anyone have in terms of going forward or not?
I want to go forward with repair because I just hate seeing the chassis, heat sink, transformer and lateral MOSFETs go to waste. What advice does anyone have in terms of going forward or not?
When I run into an amp doing this, I look specifically for the DC block in the feedback network (which typically sets DC gain to 1). This cap normally has very little DC bias (just the offset voltage) and it can go bad just because of lack of DC bias. Input DC block may be in just as bad a shape for the same reason, especially if a crap brand was used, but in that position you may or may not even notice the capacitance reduction. From feedback input to ground you will, because the required impedance is lower and it turns the amp into an active high pass filter if the cap is “way too small”. If the amp uses a DC servo, it’s integrating cap can go bad and produce frequency response anomalies or even instability. Film caps are often used there (even though it’s big and expensive) just because of sensitivity to this failure mode.
If local decoupling caps are going bad, be on the lookout for oscillations. If there are stability issues, look there. When the main filter caps are bad (they may use better ones here, as they won’t be SMT - although they are often the ones that need changing) the amp will not put out full power. Usually it won’t outright hum, but may have audible hum and buzz as volume increases due to supply ripple increasing rapidly under load. They may be out of spec but still work “well enough”. Tough call without actual measurements. These are usually the lion’s share of the cost of a recap. I never change these unless an amp needs it. The only test I’ll perform for this is just measuring short term sine wave output power. If it’s within spitting distance of spec, they’re in good enough shape.
If local decoupling caps are going bad, be on the lookout for oscillations. If there are stability issues, look there. When the main filter caps are bad (they may use better ones here, as they won’t be SMT - although they are often the ones that need changing) the amp will not put out full power. Usually it won’t outright hum, but may have audible hum and buzz as volume increases due to supply ripple increasing rapidly under load. They may be out of spec but still work “well enough”. Tough call without actual measurements. These are usually the lion’s share of the cost of a recap. I never change these unless an amp needs it. The only test I’ll perform for this is just measuring short term sine wave output power. If it’s within spitting distance of spec, they’re in good enough shape.
That is why we diyaudio. You can instead buy a class D amp, sound suspicious and doomed to fail in 2000 hours or less, for $200-250. Then send this classic to the landfill. The tools to re-ecap are about $100, include safety glasses for solder splashes. Reading glasses if you are over a certain age. I peel off surface mount caps with a angle end pick. I use solder paste going back, wire solder is too messy. Parts including the expensive rail caps might be $100. Use digikey, newark, mouser, or alliedelec.com. Not ebay or alibaba. I buy electrolytic caps with service life >3000 hours so I do not have to do the job 4 times in my life like I did buying storefront caps on my ST70. Mark + with a sharpie on board or on the printout of the picture you took, e-caps put in backwards blow the seal and leak.
Just started looking at YouTube videos and removing smd caps. May be the excuse to buy a hot air rework station for removal. I have a Haako for resoldering and plan to buy paste solder and kiwi is flux and applicator bottle. Cost is approaching 1/2 cost of the repair, but I will at least have tools.
One thing important to first jobs & new skills. I would change 1 or 2 parts at a time, then re-apply the power input source and (trash) speakers. The question, did this part change make the sound better or worse? If worse, you can be pretty sure this one part you changed is the source of the problem. What is the problem? You can look carefully, you can perhaps rework the solder joint, you can ask questions here.
Some designs are easy to test. I have had some successes. Some designs, both sides of the boards are not available for inspection without a lot of work, and hooking the power, sound source, and speakers up is a big problem. I have had jobs that defeated me, like the color PC terminal I liked so much that was displaying weird and I changed about 40 e-caps. It was so hard to get the case on and off, that one defeated me.
I have recently started a re-e-cap of a 300 watt PA amp with a switcher supply. Works fine now, but something is doomed to fail at ~10000 hours life & 25 years. Was totally wrapped up in dust. Switcher supply is so dangerous to work on, I built a whole wood frame to hold the main board vertical with both sides available, and add and remove the input, speaker wires, and AC power, safely and quickly.
Some designs are easy to test. I have had some successes. Some designs, both sides of the boards are not available for inspection without a lot of work, and hooking the power, sound source, and speakers up is a big problem. I have had jobs that defeated me, like the color PC terminal I liked so much that was displaying weird and I changed about 40 e-caps. It was so hard to get the case on and off, that one defeated me.
I have recently started a re-e-cap of a 300 watt PA amp with a switcher supply. Works fine now, but something is doomed to fail at ~10000 hours life & 25 years. Was totally wrapped up in dust. Switcher supply is so dangerous to work on, I built a whole wood frame to hold the main board vertical with both sides available, and add and remove the input, speaker wires, and AC power, safely and quickly.