Picking a victim for my first vintage re-cap, repair. Suggestions wanted!!

[Danzilla]

A little background first. I have some decent experience with soldering on a amateur / hobbyist level. I've done 'build your own radio!' and other kits back in the day, and repaired a few items here and there with obvious faults like devices with electrolytic capacitors from the 90s. I own my own DMM and 'scope, in addition to a soldering station. Plus, a wild find at my local Salvation Army. An unused Hakko 808 desoldering gun kit (in it's case with everything for $10!), that I mean to break in. (I have used wick or Soldapullt in the past.)

So I shop resale and garage sales sometimes and HAVE ALREADY picked up a number of partially working pieces for not too much. I'd like to make one of them my next project, so I was looking for opinions on the best choice to start with. Best is obviously relative, but with a few main points:

A) would like to gain a little more experience before tackling any particularly tricky or valuable piece. So not necessarily the most valuable one first (though yes, none of these are heavy hitters.)
B) at the same time I don't want to really waste my time putting work / parts into a model that isn't worth it, (ie. ROI.)
C) Big plus for any piece that might have particularly well discussed / described steps for refurbishing. So it'll be easier to follow for my first effort with detailed parts lists and replacement choices being a obviously help.
D) Anything else I'm overlooking??

Finally, here are the contenders I'm considering. Mostly just cosmetically inspected and tested for output with AUX input and tuning. (ie. didn't test phono, tape, etc)
Kenwood KR-3600. Fair condition with scratches and lightly dinged corner. Works with speakers A, but use B or A&B and no output. Tuning barely works, but does pickup a few stations faintly.
Yamaha CR-820. Very nice condition (NM?) and works. Lamps out. Tuning quite bad only really manages 1 FM station, even with external antenna.
Akai AA-1050. Just picked it up. In kinda rough condition. Scratches on front, small burn mark on top (cigarette?). Rusted hardware (screws & a couple other pieces in back.) Works on left channel but not right for all amplified outputs (speakers A, B, C, and even headphones.) Lamps out. Didn't test tuning yet.
Denon PMA-757 integrated and TU-747 tuner. Black metal finish (no wood (hehe)) in fairly good condition with no stand out damage. Have had the longest and don't remember exactly the working condition. Think the amplifier was at least partially working with few indicator lamps out. Don't think I even tested the tuner.

Thanks for looking.

D.

PS. Should this be in DIY instead? Was thinking DIY meant build your own, like speaker design and whatnot, but maybe I was mistaken (after taking a quick look.)

 

[jheu02]

SS is fine for the thread.

Thoughts...

KR-3600 looks to be a fairly simple receiver, but there's only a schematic on hifiengine.
CR-820 has full manuals, and seems uncrowded on the insides
AA-1050 - not working on one side might be harder to diagnose as a first project
PMA-757 - manual available and no tuner section to deal with. Most recent, so parts if needed might be more easily sourced.
TU-747 - only an owner's manual unless you can do an alignment, you may not want to mess with it

I'd say for your first recap, go with the Denon integrated due to SM, age, and no tuner. The boards may be easier to work on too since they're newer...some older gear has easily lifted traces.

If you're just wanting recap practice, go find a cheap thrift store unit and practice desoldering and resoldering even the old caps back in place before you work on gear you may want to keep.

 

[ickyfrog]

Good choice for your first recap is a vintage amp in the 20-30 watt range. It will have less total parts. Start with a fully working amp for your first project, learn troubleshooting later. A 20W amp realistic or whatever from eBay will not cost much, and no worries if the project fails. Just make sure before starting that you can find the schematic online (hifiengine or elsewhere). You can learn about selecting and replacing capacitors, discharging the main power cap, transistor substitution, adjusting bias and measuring DC offset. Get lots of solder wick. Replace any bulbs with LEDs. If you want to learn more, replace the transistors also. But stay away from replacing parts on am/fm tuners, that’s voodoo. Tip, only replace 2-3 parts at a time, then play your amp to test it. I keep a pair of used of old minimum 7 speakers on my workbench for this purpose. Don,t connect your best speakers until project is completed. Good luck !

 

[Harvestor]

Technics SA Receivers

 

[Danzilla]

Thanks for the suggestions, but with 4 units already on hand, I'd prefer to start with one of those rather than to buy one more just for the practice. I am familiar with electronics to some extent (be a bit odd to own a soldering station and an oscilloscope, or to even know what a desoldering gun is otherwise), but more with digital design (FPGAs, VHDL, etc) than analog, and do have enough soldering experience that I don't expect to have problems in that area (though with room for growth to be sure). When talking about gaining more experience I meant more with troubleshooting circuits and components and making any adjustment that might be needed.

I'm leaning towards the Kenwood as an inexpensive starter (BOTL?) or maybe the AKAI just because it's already cosmetically screwy (though possibly the best of the bunch build-wise.) Less likely to pick the Yammy because it's in really nice physical condition and would be a shame to screw it up, or the Denon because... well... because... there are two pieces and so twice the work!!

 

[Blue Shadow]

The CR-820 has one cap hidden behind the transformer which must be moved for access to the cap. see it on that finger of the circuit board that goes behind the transfo on the diagrams.

 

[avionic]

Akai AA-1050. Just picked up it, in kinda rough condition. Scratches on front, small burn mark on top (cigarette?). Rusted hardware (screws, a couple other pieces in back.) Works on left channel but not right for speakers A, B, C, and even headphones. Lamps out. Didn't test tuning yet.

 

[rickl]

My guess the kenwood would be the easiest to fix. typically if speaker A works, the amp is fine but the speaker switch is dirty. Clean it.

Avionic's suggesting the Akai mght provide a great one to learn how to replace outputs, drivers, ...

The Yamaha might be a good one since it is in very good condition. Go over to the yamaha manufacture forum for yamaha fanboys help. They are very helpful. Tuner calibration will require some advanced tools but might be good to learn on.

I noticed you didn't list a dim bulb tester (DBT). I'd suggest making one to help your troubleshooting.

 

[Tom B]

The Akai would be the best start for someone just starting. There is most of the service manual there on hi fi engine, so you will be able to set bias and DC balance pretty easy. My experience with Yamaha's are that they can have some tough problems in the FM bsection so a bit tougher than most others.

 

[avionic]

Go over to the yamaha manufacture forum for yamaha fanboys help

Why?

 

[llwhtt]

Get the one that has a Service Manual available and the LEAST amount of unobtainium parts.

Craig

 

[Danzilla]

Get the one that has a Service Manual available and the LEAST amount of unobtainium parts.

Craig

Only one I haven't found a service manual for is the Kenwood 3600. Only a system schematic.
Unless I can find where someone else mentions it, I wouldn't know where to start figuring which system's parts will be harder or impossible to replace.

 

[jheu02]

I'd still go for the integrated. SM available, more recent parts and boards. The tuner won’t really need much done to it if it's working already and can be used until you finish the other gear.

However, if you REALLY want to dig into something, the Akai will also require troubleshooting to get it working first and then recapped/rebuilt. If you don't currently have a stock of parts on hand for initial troubleshooting, you may end up making several orders along the way as you won't know for sure what's causing the issue at first

 

[llwhtt]

I would stay away from anything with an STK, TA, or any other output module. If you are not interested in AM or FM definitely go with an integrated amplifier.

 

[rickl]

Only one I haven't found a service manual for is the Kenwood 3600.

After you get one or two fixed, a schematic will be enough to get receivers like the kenwood working again. i checked the schematic and it doesn't look to complex. Might want to hold on to it for a future project.

Tuners always add more complexity. Which ever you choose, there will be people here to help. Plan to get it working using the AUX input then progress to the tuner and phono. Everything else should be working with a simple switch cleaning.

 

[Danzilla]

Seems I have more reasons to NOT start on the others, so looks like it'll be the AKAI AA-1050 first. It might have been owned by a smoker, for a little while at least, as wiping off the top (with the burn mark) showed a lot of brown residue. Will give it a more thorough test and look around to see if I can find anyone that has detailed the process. Some photos of my unit (hehe) for anyone interested...


Anyone know, is this vinyl on top of the wood case? Someone else insisted that was true of the AKAI systems (at least of this vintage). I ask because I tried to thin the burn mark with light sanding, but didn't want to take off much if it's really just vinyl.

 

[Oldsansui441]

Yes, it will be vinyl. Hope it all goes well for you on the Akai, it is likely the best sounding unit out of the ones you have.

 

[avionic]

Seems I have more reasons to NOT start on the others, so looks like it'll be the AKAI AA-1050 first. Seems like it might have been owned by a smoker, for a little while at least, as wiping off the top (with the burn mark) showed a lot of brown residue. Will give it a more through test and look around to see if I can find anyone that has detailed the process. Some photos of my unit (hehe) for anyone interested...
View attachment 1337250 View attachment 1337251 View attachment 1337252 View attachment 1337253 View attachment 1337254 View attachment 1337255 View attachment 1337257 View attachment 1337258

Anyone know, is this a vinyl veneer on top of the wood case? Someone else insisted that was trues of the AKAI systems. I ask because I tried to thin the burn mark with light sanding, but didn't want to take off much if it's really just vinyl.

Can you follow a schematic and own a multimeter?

 

[merlynski]

I don't know about the ones you listed, but:
Pioneer SX-780, basic, simple, one main PCB mostly accessible from both sides. It does have STK-0050 modules, the originals of which are technically "unobtainum" but there are upgrade/replacement kits discussed extensively here on AK. Those receivers are well documented here on AK. 45 WPC and can be had (partially- or non-working) under $200 if you are patient.

 

[avionic]

I don't know about the ones you listed, but:

Those listed are those he has on hand.