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Pioneer A-717 with no power

Branislav B

Branislav B

Active Member
Dear guys,

I would like to ask you if any idea what is the problem with my Pioneer amplifier A-717....

Simply, there is just 230V going in first half of the power board, but nothing more. No further voltage, totally dead.Led diode if off. Fuses and rectifiers are ok.

Any suggestion what is the issue please? Capacitors, transistors to check on power board?

Thanks a lot for your feedback.

Branislav
 
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With the unit unplugged:
On the Fuse board AEK-400 check for continuity ( 0Ω ) between pin 14 (purple wire) and pin 9 (yellow wire) to verify the internal power transformer thermal fuses are good.
 
merlynski said:
With the unit unplugged:
On the Fuse board AEK-400 check for continuity ( 0Ω ) between pin 14 (purple wire) and pin 9 (yellow wire) to verify the internal power transformer thermal fuses are good.
Click to expand...
Hi Merlynski,

I just checked both circuits and both are open, so the thermal fuses are are dead. Any way hot to replace them or just to purchase new transformers?
Thanks a lot,

Branislav
 
Branislav B said:
Hi Merlynski,

I just checked both circuits and both are open, so the thermal fuses are are dead. Any way hot to replace them or just to purchase new transformers?
Thanks a lot,

Branislav
Click to expand...
If you can find a donor machine somewhere you might find some used transformers. I have seen people talk about opening (disassembling) transformers up and replacing the thermal fuses. Sometimes they can get to them, sometimes they are too buried in the windings and are in-accessible. Is this a unit you have had for a while that was working and failed, or something you acquired hoping to repair it? Are there any signs of overheating? I suspect the main fuse was replaced with a larger one because the original fuse blew. So instead of troubleshooting the problem the fuse was wrongly replaced and the overload blew the internal transformer fuses.
You could have some custom transformers made, but that is probably more expensive than you can tolerate.
I have some other ideas but they risk causing a fire, so I don't recommend them.
 
Hi Merlynski,

It was aquired machine with electrical issue... hoping to repair such a beautiful amplifier . Not open/repaired by previous owner,he said.
The transformers are epoxied, so quite a lot of work to open...what about adding external 2A fuses between two purple (pins 7-14) and two white (pins 8-9) wires to bypass thermal fuses?
 
The internal thermal fuses are there to protect the unit from a fire caused by an overheated transformer, their electrical blow point was probably higher than the main fuse. External fuses would not provide thermal protection. Since they are in series with each other, and the main 4A fuse, they (2A) would pop before the main fuse,which would be very frustrating. What value fuse is installed in the main fuse holder FU1 at this time?

Can you post a picture of the transformers and the fuse PCB AEK-400, top and bottom if available and possibly useful, please?
 
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Hi Merlynski,

FU1 is as it should be = 4A. Photos attached.

Thank You,

Branislav
 

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Thanks for the pictures! and Welcome to Audiokarma!
I have some suggestions, if you understand the risk (fire) from bypassing the thermal fuses:
If your Country has laws restricting modifications of Mains wiring, consider carefully what you are choosing to do. upload_2020-8-7_13-46-52.gif
Post the AC voltage from your wall mains connection:
Unplug unit from wall, Measure resistance from the primary winding side to ground, It should be (much) greater than 2MegΩ.
Put 4A fuses, just like the main fuse, across the pins (bypass) for the thermal fuses.
Build or acquire a DBT: Dim Bulb Tester diagram pictorial... please feel free to copy and post.
Use the DBT the very first time you power up to test and troubleshoot this unit, and keep it on the DBT until it has been confirmed safe to go to full mains voltage.
Post when you have a DBT built if you want to continue. I believe this unit can play music again, unless the transformers are ruined from overheating.
It is up to you to continue or not :D
 
Thank You for your proposal. It seems that this test should check the load/quality of insulation of primary winding if ok? Am I right? I will keep you informed.
 
Branislav B said:
Thank You for your proposal. It seems that this test should check the load/quality of insulation of primary winding if ok? Am I right? I will keep you informed.
Click to expand...
Yes, if any of the windings have a leak or a connection (short) to the chassis they are bad and not usable. If the primary winding are good, the secondary windings need to be checked, but that may be a bit more difficult.
 
Hi Merlynski,

I have tested primary winding for one hour with 100W bulb and then checked secondary winding with ok result as well. So I have by-passed the thermal fuses and amplifier switched on and fully working.
Thank You so much for your help to identify the issue and test if transformers will be able to work even if no thermal fuses operational.
 
Merlynski; you know those thermal cutout switches used on Bathroom heater fans, or RV Furnaces (cutoff about 150-180*F). use a lower temp unit due to thermal propagation (the core will be hotter than the case) Attach one temporarily to the side of the transformers, to check operation and select temp that holds up under normal operation, but kicks out when cranked too hard? You'd probably get some thermal protection (maybe, maybe not), but just quick thinking, better than a fuse on the power supply with no temp overload. The only drawback to it is when temps go back down, it kicks in again. Are there thermal switches that can be manually reset? Or am I blowing smoke out my backsides, and everyone is staring at me with 3 heads and holding their noses?
 
@larryderouin You been reading my mind? There are a bunch of them on Amazon, $10 to $12, various temps, manual reset button. This one I found: https://www.amazon.com/Bradford-Whi...ds=thermal+reset+switch&qid=1598372888&sr=8-8 trips at 170 deg according to a review. The biggest downside I can see is they are rated at 36v for controlling the usual 24vac driven gas controllers on furnaces and water heaters, etc. It would require a circuit addition because it would not be safe to connect it to ac mains voltage.
It would be easy enough to attach with some thermal conductive adhesive.
 
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