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May Have Found the Problem - Sanyo P55

K

KeithTr

AK Subscriber
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Working on a Sanyo P55 power amplifier that I got quite inexpensively as it was not working properly. It came out of protection but with a bad signal on one channel. It may still not work properly as I found quite a few cold solder joints and a couple of caps way out of spec and it's a real pain to disassemble and it's not reassembled yet. So I replaced all the capacitors trying to be really careful about orientation so I don't have to disassemble again. Plus, the power cord was stiff as a board. But I think these pics may have something to do with the issue on the right channel. Funny thing is there's no rust in the unit and the other relay showed no signs of oxidation.

Separately I do have two question about wiring polarity and testing. I'm installing an IEC inlet and planning on not using the ground. This unit had a non-polarized plug. Can I assume that it doesn't really matter which side of the switch receives the hot side from the wall? Thx in advance.

Secondly, this unit has nearly unobtainable Hitachi MOSFET outputs. All test good. When I hook this back up, can I run a dim bulb test with the output boards not connected and have it be meaningful? Is there anything else I should check before connecting the ouputs?

Thx again for your help...K
 
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Power up the relay coil and measure the contact resistance on the two different contacts. That will tell you if it's bad. Resistance should definitely be <50 milliohms. I prefer <20.
 
Namlook said:
Power up the relay coil and measure the contact resistance on the two different contacts. That will tell you if it's bad. Resistance should definitely be <50 milliohms. I prefer <20.
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Yeah, not going to even try to repair that. Will replace both relays. There's an Omron that apparently drops in when you clip the top row of contacts.
 
Yeah. That relay is junk, throw it in the trash. Since your unit is functioning, you have no need to DBT it.
It would be a very good idea to replace the bias trimmers and pull the outputs, clean them, and reinstall them with new micas and thermal paste as I'm sure the original paste has completely dried out by now.
 
tarior said:
Yeah. That relay is junk, throw it in the trash. Since your unit is functioning, you have no need to DBT it.
It would be a very good idea to replace the bias trimmers and pull the outputs, clean them, and reinstall them with new micas and thermal paste as I'm sure the original paste has completely dried out by now.
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This has been a relative pita to disassemble and I'm sure the reverse will be as well. But outputs already out, cleaned, and boards cleaned and touched up plenty of cold/cracked solder joints. Given pain to take apart, I also replaced most capacitors with 105 degrees given it also runs hot (main boards are vertical and get plenty of heat. Planning to replace bias trimmers and remount outputs with silpads (though I could go mica/compound also). I do want to dim bulb it again when back together as I did a lot of touch up soldering and while I was pretty careful and tried to inspect all, I could have introduced a problem.

Only remaining plan issue is that old cord (non-polarized) was shot so I am replacing with an IEC inlet and not using the ground. But even though I;ve read some threads here, not quite sure which side of the plug the hot should be wired to - I'm guessing left prong per diagram as that seems to go to switch first. But this unit has circuit breakers, not a fuse, and normally I think you'd wire to go to the fuse first. if you care to comment, I'm attaching that portion of the schematic...

Sanyo P55 power schematic.jpg
 
Hot should go to the power switch. The breakers will function just the same regardless. TBH, I think I'd rather see fuses rather than breakers.
 
I was also going to suggest instead of using an IEC C13/C14, look into IEC C9/C10 for your AC connection.
 
That's a good suggestion for the next one (already mounted the IEC) - but probably harder to find cords at a decent price. But it would preserve (presumably) the original non-polarized wiring scheme.

Seems to me from just mucking around with a multimeter on resistance that it really doesn't matter - both prongs coming in from the outside seem to end at different sides of the switch.
 
KeithTr said:
That's a good suggestion for the next one (already mounted the IEC) - but probably harder to find cords at a decent price. But it would preserve (presumably) the original non-polarized wiring scheme.

Seems to me from just mucking around with a multimeter on resistance that it really doesn't matter - both prongs coming in from the outside seem to end at different sides of the switch.
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I recently purchased a sanyo p55 and have been having issues with the speaker selector. I cleaned the switch but it didnt seem to help. I believe the issue is with the relays as they dont always click, but am not sure where they are located? I didnt see them when I had the cover off. Also were you able to find replacements? Thanks
 
Yes, the relays are on one of the two amplifier boards (I believe its the left one looking at the amp from the front). In order to access them, you have loosen and remove the heat sink assembly, which attaches to the amplifier boards. I ended up removing both the heat sink assembly and the circuit board that holds the output transistors (one on each side). But you can flip over the amp boards with the heat sinks attached to get access to the other side of the amp board. Sounds a little complicated, but once the heat sink screws are out, you'll see what I mean. And you will have to remove the bracket that holds the filter caps. There is a drop in Omron replacement for the relays - I'm trying to remember if I had to clip off one row of the relay contacts that is not needed (I've done that with Omron's in the past) but if you search this site for threads on the P55, you will find someone that mentioned the exact drop in replacement - still available at Mouser or Digikey. I'll try to take a look to see if I can dope out which one I used.
 
evilstue said:
Thanks this helps a ton. I think i will take a look at it over the weekend. I appreciate the help!
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NP. Also, be sure to check the amp boards for solder joint quality - I've seen examples where they were absolutely fine and others where lots of touch up was needed. While it doesn't show everything, try searching YouTube for PrimeHiFi - a guy who put up some great restoration videos a few years ago and one of them was the C55/P55 combo. You will be able to see what I mean by flipping up the board. It is even easier if once you free the heat sink, you separate the heat sink from the amp boards but be careful to take lots of pictures and maybe write down the order in which you deconstructed the device in order to reassemble. It's not that hard, but there are quite a few steps. I also left off the cardboard strip that i think is there to protect the output transistor boards from getting dust or debris, but these amps tend to run hot (lots have lost their freon in the sealed heatsink) and it probably improves airflow to leave it out. Also, consider putting a computer below or on top when done - a decent low speed quiet single or dual fan will greatly reduce the heat and make everything last much longer.

PS - these are great "under the radar" MOSFET amps - good power, very clean output, relatively low profile.
 
Ill def check out primehifi, having a good visual idea of what I need to do before hand is very helpful. Also, I like the idea of using a pc fan to keep things cool and I have several of them laying around. Might as well use them. I also got the c55 pre and t55 tuner with the amp and was able to listen to them for a while before the relays started acting up. Im very impressed with the sound quality and build quality. I never expected that Sanyo gear could be this good. Im looking forward to have this thing working again!
 
evilstue said:
Ill def check out primehifi, having a good visual idea of what I need to do before hand is very helpful. Also, I like the idea of using a pc fan to keep things cool and I have several of them laying around. Might as well use them. I also got the c55 pre and t55 tuner with the amp and was able to listen to them for a while before the relays started acting up. Im very impressed with the sound quality and build quality. I never expected that Sanyo gear could be this good. Im looking forward to have this thing working again!
Click to expand...

For a very brief time (I think less than 3 years), Sanyo created a "skunk works" to try to challenge the top of the line of their competition. Result was C55, T55, and P55. I think all are sleepers with respect to quality and price. Some don't care for the looks of the P55, but I actually sort of like it - there are a couple of Accuphase units with a similar meter system. They did use plastic side panels, but the C55 and t55 side panels are aluminum, like the fronts. The biggest issue seems to be the P55 freon heat sink, which can run quite hot if it loses its freon, which is not surprising after so many years (and with the output transistors mounted on the bottom of the unit.) But I've found that a quiet fan assist is enough to keep it running quite cool - and that prevents a lot of issues, such as stressing certain solder joints etc. On my scope, these units check out very favorably with almost everything else I've looked at once they are properly adjusted and cared for.
 
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