Another Sansui 771 And Some Useful Recapping Tips etc

[@sethfarry2661]

This guy is awesome. Always appreciate and value the time of smart folks

[@andthepoetliftshispen5752]

Great video, thanks for the help! I'm beginning a re-cap on a 771. I have 15 years as a tech, repairing medical, aerospace, and other devices. One thing I never had contact with before is a conformal coating on any board. I was always trained to clean the work areas before and after with isopropyl alcohol and a parts brush. A few years back I was given a Harman Kardon amp in which the board was burned thru and a high current trace was destroyed by a resistor. I was attempting to use ample gage wire to replace the trace. I began the work by cleaning the area with isopropyl alcohol, but knew nothing of a conformal coating. The area turned to mush, and the more I realized something was wrong, it got worse until I decided it was a lost cause anyway. Now that I'm aware of these coatings, I'll test a safe area of the board first. Do you find these coatings on vintage equipment very much - like the 771? I don't want to encounter this again! Thanks!

[@retroelectrotech]

Glad the video is helpful, and good to hear you're working on your 771, it's a nice receiver / amp. In regard to board cleaning, when I'm removing flux, or some other miscellaneous crapola from a board surface (in most cases, and I've cleaned tons of boards), I've had no issues with 99% anhydrous alcohol and a brush. I do it all the time in this vintage gear (etc.) and haven't had any coatings breakdown and turn to mush etc. There's always the exception to the rule, so as you know / mentioned, it's a good idea to test your solvent on a small area. Again, you should be fine with this equipment. Thanks for chiming in, and my best to you and your re-cap project, enjoy the tunes 🙂

[@andthepoetliftshispen5752]

@@retroelectrotech Once I get going on my project, I plan re-flowing all solder joints on each board to compensate for thermal expansion and shock stress from years of use. I'm confident my soldering skills will not introduce unforeseen problems. I wonder if this step alone might even negate the need for a recap job - altho I still will. Do you have a favorite reasonably priced solder station? I always had great success with Weller stations 20 years ago, but reviews show their quality has suffered greatly since they began building them in China. I also love Metcals, but unless I can find a used one, they're out of my price range. Tried Hakko and a few Chinese models over the last 5 years on a company autonomous vehicle project, but they seem to lack acceptable tip heat control. No matter how I try, I can't flow a good joint. Would never attempt them with to trust on my Sansui boards without pad damage. Any thoughts? Thanks again!

[@retroelectrotech]

@@andthepoetliftshispen5752 That's definitely a good course of action going through and reflowing solder joints. I find a very high percentage of connection issues present in one form or another. I to appreciate the quality of the old soldering stations that held up to the demands of day in and day out heavy use, I've owned several. As you mentioned, if you want to stick with an old battle proven station, I'm sure you can find one on "the auction site" that is still in decent shape. At present, I use the Hakko FX-888D. I haven't had any issue with unacceptable performance maintaining tip temp, it's been a solid, stable unit with a nice smaller footprint. I can't speak for all Hakko stations, because I haven't owned anything other than the station mentioned and a Hakko de-soldering gun, the FR-301, which does a good job if properly maintained. Actually, if I'm not doing a ton of back to back de-soldering, I actually prefer to use a manual vacuum pump or wick, but I digress. Again, the Hakko soldering station mentioned has done well subjected to the volume of work I throw at it. There are situations when I need to tackle some large areas of circuit board and chassis soldering etc., that call on me to break out my old Weller 8200-N (Gun). Otherwise, I get by just fine with what I mentioned 🙂

[@andthepoetliftshispen5752]

​@@retroelectrotechThanks again, bud. I'll look into the Hakko, and if I can still find one, I'll buy my old reliable pre-China Weller CPT! Happy trails!

[@josephlalock8378]

11:50 i wish someone could do a video on which cap to use where. it would be extremely helpful to me. i'm fairly new to the hobby and some 'lytic cap locations are obvious to me and what to use, such as c01, which i know i could use a film or UKL,UFG,UKT because it's in the signal path. and power supplies are easy to identify but i do wonder if switching power supply caps (UPS,UPJ,UPW) are sufficient for non switching psu's. but more specifically, what would be a good cap for c05,c09,c13. i would personally throw a UKT in each location and be confident it would be fine. possibly a UPM or UVZ for c13 depending on what i have in stock. any input would be helpful.

[@retroelectrotech]

Hello Mr. Lalock, as I go through various circuits in future videos, I'll try to mention why a particular capacitor is better suited in a particular application etc. (when performing a recap and or just replacing a bad cap). Nonetheless, You sound like You have a good handle on the fundamentals obviously. Otherwise, I wouldn't be too concerned (within reason) about the caps in the positions You mentioned. I assume You're referring to the driver board, as there are identically numbered caps on the other boards as well (although not necessarily "lytics"). The areas of circuitry You're referring to are not overly critical in regard to the original electrolytics and what You install as replacements. Just use good quality, (obviously) reasonably low leakage caps with a reasonably low ESR and all will be well. As You know with caps in the audio path (for example), it really comes down to preference once You understand what constitutes "audio grade caps". Of course that subject is HUGE and could go on and on throughout eternity. However, for the most part, and as You probably already know, an "audio grade cap" is optimized to minimize distortion or other unwanted sonic characteristics within the audio spectrum, kinda obvious right? However, what is considered the optimal audio grade cap for one person in a particular application, may not be for the next guy, which is where all the "hair splitting" comes in. Again, there are a lot of good caps out there well suited for the audio path (among other applications), and You have some in Your inventory. I use a variety, Panasonic FC's, Nichicon Fine Golds etc., depending on what I have in stock and what I can find that's not on "back order" nowadays. So, I really try not to pitch a particular brand and or series of cap, because it's subjective once all of the "audio grade" specs / characteristics are understood. Once again, You'll do well with the quality caps You have on hand, especially in the application You inquired about. If You were dealing with higher frequency stuff, sensitive tuned circuitry and otherwise precise "regulatory functions" etc., then You'd have to pay much more attention to the effects of ESR, ESL (among other things) and how such characteristics / parasitic effects could impact functionality. As far as Your low ESR caps used in non-SMPS applications, in most cases it shouldn't matter much, other than more expense, since them low ESR caps tend to be a bit pricier. Of course, there are some circuits / applications where too low an ESR could cause issues, such as with LDO regulators for example (stability issues), but again, the subject of cap type (based on specs / characteristics) and in what application vs. all the possible effects is impossible to cover in one swoop of course. Otherwise, my best, You're on the right track and it looks like You have the bases covered. 🙂

[@josephlalock8378]

@@retroelectrotech thank you for the reply, it helps! . . . and yeah, the whole "caps on backorder" is pretty frustrating. it's pretty annoying having to pay 2 shipping charges because one place just does not have what i want/need. i do have some panny fc/fm on hand too and some elnas but i mostly stick to nichicon for 'lytics. mainly wima and kemet for signal path films and i do have some panny films in stock too for bypass caps in power supplies. i don't fall prey to capacitor snake oil, quality caps and figuring out the right cap for the right job is my goal.

[@retroelectrotech]

@@josephlalock8378 My pleasure, glad to be of help when I can. Yes, the supply chain / production issues, which in turn are causing shortages (all across the board) are definitely frustrating and are a big concern at many levels. The thing I enjoy the least about running this full time "brick and mortar" shop, is parts shopping online, especially in this day and age. It burns up a lot of time I need to devote to "the bench". All the above caps You've mentioned are good choices for the audio circuits we restore in this vintage gear, and in turn, bring back to an acceptable level of reliability. Thanks again for chiming in, I'll have some cool gear hitting the bench soon🙂

[@davidbernier5782]

Hello sir! I am writing because I just picked up a cheap 771, and it has a few bulbs out in the display. (Additionally, the plastic plate that the lights shine *through* has fallen a bit.) My goal is to replace the lights. At first I thought it would be a simple job, a good introduction to working on a receiver for my first time. However, I'm having lots of trouble even figuring out how to access the lights! I know that the off-white plastic housing needs to come off, but I'm not sure how to get it off. I have experience working on cars, so I'm confident that I will be able to do the work once I know what to do. How do I go about this? Is it the two screws on the top of the plastic piece? Any guidance that you would be willing to provide would be most welcome. Thank you for your time, David in Virginia

[@retroelectrotech]

Good afternoon David, provided is a link to a video that might help You out, my best to You 🙂 kzbin.info/www/bejne/aom3nY2gmZ15aMU

[@rickkestner7886]

Too bad he could not figure out how to focus the camera!