I have this amp and I believe the relay is bad. Amp powers up, but no output to speaker terminals and headphone jack. I'm not sure which pins are the relay coil but checking with an ohmmeter I found no continuity between any pins. Does anyone have or know where I can get the datasheet or pin-out for an ASR-020 relay?
Also, the tuner flywheel is really stiff, I've pulled it out and used cleaner fluid, lighter fluid and WD-40 lithium spray on it which seems to help. Are there any other recommendations?
Any advice would be welcome.
Also, the tuner flywheel is really stiff, I've pulled it out and used cleaner fluid, lighter fluid and WD-40 lithium spray on it which seems to help. Are there any other recommendations?
Any advice would be welcome.
Last edited:
My SX-750 had the same symptoms. I found that tapping the relay gave intermittent output so I replaced it with a modern equivalent. It works fine now.
One other thing to check - do you hear a click from the relay a few seconds after power up? The click would be the relay engaging. If there's a click but still no sound then it's probably dirty/scorched relay contacts. If there is no click from the relay then there may be something amiss in the protection circuit.
Google "ASR-020 replacement" and you should get some good links.
I don't have any recommendations on the flywheel issue.
One other thing to check - do you hear a click from the relay a few seconds after power up? The click would be the relay engaging. If there's a click but still no sound then it's probably dirty/scorched relay contacts. If there is no click from the relay then there may be something amiss in the protection circuit.
Google "ASR-020 replacement" and you should get some good links.
I don't have any recommendations on the flywheel issue.
Last edited:
Hi "Art",
The protection circuit is probably working for a reason. Most commonly, DC voltage at an amplifier output.
Do you have any test instruments, and are you familiar with using them?
If not ... find a good audio technician. Other technical trades don't have the specific knowledge that will save you money with this repair.
This sounds like a receiver that you came across in the trash or stored somewhere. Getting it to work is normally more of a restoration than a repair as multiple things will need attention. So first, stop spraying stuff around it!!! There are parts that if you get anything in them, say goodbye to the tuner, or hello to an expensive fix. If you won't or can't take it to a tech, try giving it to someone who will or has the knowledge and equipment to restore it properly. Otherwise you are just completing the destruction of this poor thing.
-Chris
The protection circuit is probably working for a reason. Most commonly, DC voltage at an amplifier output.
Do you have any test instruments, and are you familiar with using them?
If not ... find a good audio technician. Other technical trades don't have the specific knowledge that will save you money with this repair.
This sounds like a receiver that you came across in the trash or stored somewhere. Getting it to work is normally more of a restoration than a repair as multiple things will need attention. So first, stop spraying stuff around it!!! There are parts that if you get anything in them, say goodbye to the tuner, or hello to an expensive fix. If you won't or can't take it to a tech, try giving it to someone who will or has the knowledge and equipment to restore it properly. Otherwise you are just completing the destruction of this poor thing.
-Chris
Relays generally do fail in old equipment like this, but not in the way you think. The contacts wear out, making intermittent contact.
When the relay fails to engage completely, though, it's usually an indicator of a fault elsewhere (though the relay is most likely bad, too).
This amp uses STK modules instead of output transistors, and these very commonly fail, due to overload, etc. If they do, the relay will not engage and you'll get no sound.
Problem with these STKs is that there are no parts available, since they've been discontinued a long, long time ago. Plenty of fakes about, however, and these are commonly bought by less informed people. They always fail very easily, if not right away. A real shame.
When the relay fails to engage completely, though, it's usually an indicator of a fault elsewhere (though the relay is most likely bad, too).
This amp uses STK modules instead of output transistors, and these very commonly fail, due to overload, etc. If they do, the relay will not engage and you'll get no sound.
Problem with these STKs is that there are no parts available, since they've been discontinued a long, long time ago. Plenty of fakes about, however, and these are commonly bought by less informed people. They always fail very easily, if not right away. A real shame.
Anatech,
I'm a CET and work for a car audio equipment manufacturer as an electronics technician. So I'm well acquainted with test equipment and know my way around electronics, both vintage and modern day. My bench at the house is well equipped for testing and repairing audio gear.
I'm pretty sure the relay coil is open and I'm looking for the datasheet to verify the pin out.
I pulled the tuner flywheel and is no where near the receiver, so any cast off from the tuner cleaner, lighter fluid or lithium grease will not endanger the unit.
This was not found in the trash and is a friend who's had me work on several of his Pioneer receivers over the years. BTW, my name is Bill. "Art" is the name of a well respected Arthur of Science Fact and Fiction, you may have heard of him, Arthur C Clarke ring a bell? Maybe your wife is right!!!
I'm a CET and work for a car audio equipment manufacturer as an electronics technician. So I'm well acquainted with test equipment and know my way around electronics, both vintage and modern day. My bench at the house is well equipped for testing and repairing audio gear.
I'm pretty sure the relay coil is open and I'm looking for the datasheet to verify the pin out.
I pulled the tuner flywheel and is no where near the receiver, so any cast off from the tuner cleaner, lighter fluid or lithium grease will not endanger the unit.
This was not found in the trash and is a friend who's had me work on several of his Pioneer receivers over the years. BTW, my name is Bill. "Art" is the name of a well respected Arthur of Science Fact and Fiction, you may have heard of him, Arthur C Clarke ring a bell? Maybe your wife is right!!!
Hi Bill,
Cool, so you don't have a problem. I wasn't suggesting that you would. Either you have equipment and can use it, or you shouldn't be in there. Fair enough?
I know perfectly well who Arthur C. Clarke is. I used quotes since your name wasn't clear in the body of the text. It was supposed to be amusing.
Now, as for the condition of the set, you have to agree that if you didn't know where it came from, you would be wondering if it was a dumpster find. We get them often enough. You also didn't state that you removed the tuning flywheel to work on it. Most newbies don't, they just start spraying. Anyway, I hate dial cord. Better you than me!
Now, relay coils don't often go open unless they have been wet and are corroded. The coil wires are easy to trace if you pull the relay. On the PCB, there is almost always a diode across the coil. I hope that helps you out. Have you checked the amplifier stages for DC offset?
-Chris
Cool, so you don't have a problem. I wasn't suggesting that you would. Either you have equipment and can use it, or you shouldn't be in there. Fair enough?
I know perfectly well who Arthur C. Clarke is. I used quotes since your name wasn't clear in the body of the text. It was supposed to be amusing.
Now, as for the condition of the set, you have to agree that if you didn't know where it came from, you would be wondering if it was a dumpster find. We get them often enough. You also didn't state that you removed the tuning flywheel to work on it. Most newbies don't, they just start spraying. Anyway, I hate dial cord. Better you than me!
Now, relay coils don't often go open unless they have been wet and are corroded. The coil wires are easy to trace if you pull the relay. On the PCB, there is almost always a diode across the coil. I hope that helps you out. Have you checked the amplifier stages for DC offset?
-Chris
Fair enough Chris,I will get back on when I get chance.
Sent from my HTC Desire 626 using Tapatalk
Sent from my HTC Desire 626 using Tapatalk
Hey Bill,
Good luck with that set. It would be pretty neat if the relay coil was open and it had no other issues.
-Chris
Good luck with that set. It would be pretty neat if the relay coil was open and it had no other issues.
-Chris
On my amp designs I usually put a 100nf across the relay contacts to soak up any arcing. Makes them last longer.
Well, so much for an easy fix.
FYI, the initial turn on sequence is as follows:
The amp immediately powers up upon flipping the power switch, no soft start and no click from the relay. This should have clued me into a protection issue.
There is 53Vdc on either side of the relay coil referenced to chassis GND. I probed the PA3004(DC level detection IC) The following is my readings,referenced to chassis GND:
PA3004
Measured Vdc Schematic
1) 13.76 ~14v
2) N/C N/C
3) 0 .9
4) .72 0
5) 0 0
6) -7.04 -6.9
7) -.049 0
8) .47 7.4
Q26-2SC1384
E) 0 0
B) 0 .9Vdc
C) 53Vdc ~53Vdc
I measured the DC offset directly from the speaker terminals and all measured 0Vdc,also my ohmmeter measured no shorts across spkr terms or around the STK's.
I will check the Vdc on the STK's and post. I found a service manual and data on the exclusive pioneer IC's. Maybe theres still hope. Thanks or all your help so far
FYI, the initial turn on sequence is as follows:
The amp immediately powers up upon flipping the power switch, no soft start and no click from the relay. This should have clued me into a protection issue.
There is 53Vdc on either side of the relay coil referenced to chassis GND. I probed the PA3004(DC level detection IC) The following is my readings,referenced to chassis GND:
PA3004
Measured Vdc Schematic
1) 13.76 ~14v
2) N/C N/C
3) 0 .9
4) .72 0
5) 0 0
6) -7.04 -6.9
7) -.049 0
8) .47 7.4
Q26-2SC1384
E) 0 0
B) 0 .9Vdc
C) 53Vdc ~53Vdc
I measured the DC offset directly from the speaker terminals and all measured 0Vdc,also my ohmmeter measured no shorts across spkr terms or around the STK's.
I will check the Vdc on the STK's and post. I found a service manual and data on the exclusive pioneer IC's. Maybe theres still hope. Thanks or all your help so far
Well,looks like the output pins on one of the STK0050 has 28Vdc on them! I will pull the chip and see if I get output on the other channel.
I looked for a source for the STK and of course could only find them on ebay.I know it's a crap shoot, but may not have a choice. Can anyone recommend what markings or other ways to determine old/new stock? I found some that are marked STK0050II.Would they be upgraded or second generation device and would they be preferable. Again I realize there is no quarantees when dealing with eBay,but I just won't a fighting chance for this amp.
Sent from my HTC Desire 626 using Tapatalk
I looked for a source for the STK and of course could only find them on ebay.I know it's a crap shoot, but may not have a choice. Can anyone recommend what markings or other ways to determine old/new stock? I found some that are marked STK0050II.Would they be upgraded or second generation device and would they be preferable. Again I realize there is no quarantees when dealing with eBay,but I just won't a fighting chance for this amp.
Sent from my HTC Desire 626 using Tapatalk
I pulled one STK module and the amp powers up and I get audio on the other channel.I've checked around and the driver stage, and emitter resistors etc all look good. So, changing the STK should be the fix. I'm considering changing both. The good STK is an ECG replacement.
Okay, back to a reliable source for this module. Most of what I've read on other forums and diyaudio including Welcome's post are not very encouraging, and my best bet would be to find ones pulled from a parted receiver. Of course they will be few and far between.
Also, the STK0050II seems to be a good replacement judging from the spec sheet and schematic and claims to have a lower THD spec. But, again the same problem exists with vetting the source. There are some recommendations for using the STK0060 and one or two others, in the STK family.There is a knockoff a few ebay sellers are suppling branded Liberty. Is anybody familiar with this brand?
Any recommendations are welcome including a seller on ebay that you personally trust. I know ebay can be a minefield, but if you can avoid the mines there are some golden nuggets!
Thanks, Bill
Okay, back to a reliable source for this module. Most of what I've read on other forums and diyaudio including Welcome's post are not very encouraging, and my best bet would be to find ones pulled from a parted receiver. Of course they will be few and far between.
Also, the STK0050II seems to be a good replacement judging from the spec sheet and schematic and claims to have a lower THD spec. But, again the same problem exists with vetting the source. There are some recommendations for using the STK0060 and one or two others, in the STK family.There is a knockoff a few ebay sellers are suppling branded Liberty. Is anybody familiar with this brand?
Any recommendations are welcome including a seller on ebay that you personally trust. I know ebay can be a minefield, but if you can avoid the mines there are some golden nuggets!
Thanks, Bill
Have a look at this thread:
http://www.diyaudio.com/forums/solid-state/215676-diy-stk-0050-module-2.html
I have a functioning SX780 here right now on my bench if you need any voltage readings.
-john
This is also interesting, used on later STK designs:
http://www.petervis.com/electronics/stk465/imst-hybrid-ic.html
We always referred to the early STKs as "thick film hybrids" because they used conventional components AND a ceramic/phenolic pcb with a mixture of through hole and 'printed' resistors (laser trimmed often) all sealed up in a hybrid pack. Sanken/Toshiba did a lot of these for Pioneer- eg SA-7300 etc.
Then Sanyo did the next evolution, and then the IMST styles came along at the end, IIRC.
http://www.diyaudio.com/forums/solid-state/215676-diy-stk-0050-module-2.html
I have a functioning SX780 here right now on my bench if you need any voltage readings.
-john
This is also interesting, used on later STK designs:
http://www.petervis.com/electronics/stk465/imst-hybrid-ic.html
We always referred to the early STKs as "thick film hybrids" because they used conventional components AND a ceramic/phenolic pcb with a mixture of through hole and 'printed' resistors (laser trimmed often) all sealed up in a hybrid pack. Sanken/Toshiba did a lot of these for Pioneer- eg SA-7300 etc.
Then Sanyo did the next evolution, and then the IMST styles came along at the end, IIRC.
Last edited:
Hi Bill,
Look for a dead receiver. They may have one or two of those ICs. They were very popular in all kinds of sets of that era. Similar powered receivers would tend to use the same chip set. Philips-Marantz used them as well.
If you go with the a higher revision chip, make certain the pinout is the same. You can use higher rated chips in that family as well. Whatever you do, use your oscilloscope to make certain the chip isn't oscillating! You may have to change the compensation capacitors, or add supply decoupling caps. If there are unpopulated places in the PCB for capacitors, try those positions.
I have replaced more of these than I can count through the years. You should almost expect the new chip to oscillate.
-Chris
Look for a dead receiver. They may have one or two of those ICs. They were very popular in all kinds of sets of that era. Similar powered receivers would tend to use the same chip set. Philips-Marantz used them as well.
If you go with the a higher revision chip, make certain the pinout is the same. You can use higher rated chips in that family as well. Whatever you do, use your oscilloscope to make certain the chip isn't oscillating! You may have to change the compensation capacitors, or add supply decoupling caps. If there are unpopulated places in the PCB for capacitors, try those positions.
I have replaced more of these than I can count through the years. You should almost expect the new chip to oscillate.
-Chris
Here is where I'm at with this receiver. I found R259-200 ohm open. This resistor is in the emitter circuit of Q13-2SC1885 which forms a Darlington pair with Q11-2SC1775. The result is approximately 39.5 volts on the input pin to the output module.Q13,Q11 and Q15-2SA912 check good with an ohmmeter and diode check in circuit. I will replace all the three transistors including the 200 om resistor in any event. Having said that can anyone recommend suitable replacements and a reputable source and should I then replace the opposite channels three transistors?
The STK0050 hasn't been in production since the 70's or maybe early 80's, so naturally no replacements are available anymore. I mean it's been 40 years, what would you expect? 😉 I've tried some fake Ebay STKs before but it wasn't worth the effort, because in the end I always ended up with a blown up amp and the peanuts I spent on those parts down the drain.
Hi Welcome,
-Chris
Mid eighties. I was buying them from a distributor that buys from Japan. They dried up through him, then the distributors about the mid eighties. The only real chips will be from inside another amplifier / receiver.
-Chris
Just to follow up, although it's been awhile since I finished repair. I found a source for STK2060's that were pulled from another Pioneer. I think I paid $15 dollars a pop. This module has two pins for hooking up internal emitter resistors, which I didn't connect. After replacing both modules I stilled had a protection issue. I traced the problem back to an open emitter resistor in the push-pull pre driver stage. I don't recall the locator or value and will post more specific info when I get a chance to review the schematic. Also, this amp had a very stiff tuning knob, which I pulled and soaked in lighter fluid and lithium grease, after several weeks the flywheel was spin freely and worked nicely once installed. Of course the tuning string was a major ordeal!! But I managed to get everything back together, minus a couple of cover screws, Where do screws run off to, anyway?!?!?! Anyhow, it sounds great and my friend is happy to reclaim it!! Thanks for all your advice, Anatech, Welcome and Resistor-John and Nigelwright!!
- Status
- Not open for further replies.