Hi:
One of 10,000uF 80V caps opened up and seems to have partially damaged my Dynaudio Sub500 amplifier.
Replaced the cap.
The amp seems to be ok at low level but if any noise, pops clicks or even a ground loop, the amp shuts down. Anyone have the schematic for the Sub500 ?
I think something has gone funny in the protection circuit.
I turn on the amp, all is quiet. I touch my finger to the center pin of the input RCA or XLR and I hear a the 60Hz hum.
I try to connect anything that is AC powered to the amp, it immediately shuts down. Something else failed and now it doesn't even amplify.
I checked all 4 output transistors ( 2SA1943 and 2SC5200, and their emitter degeneration resistors and all is good.) This amp has too many relays!
Peter
One of 10,000uF 80V caps opened up and seems to have partially damaged my Dynaudio Sub500 amplifier.
Replaced the cap.
The amp seems to be ok at low level but if any noise, pops clicks or even a ground loop, the amp shuts down. Anyone have the schematic for the Sub500 ?
I think something has gone funny in the protection circuit.
I turn on the amp, all is quiet. I touch my finger to the center pin of the input RCA or XLR and I hear a the 60Hz hum.
I try to connect anything that is AC powered to the amp, it immediately shuts down. Something else failed and now it doesn't even amplify.
I checked all 4 output transistors ( 2SA1943 and 2SC5200, and their emitter degeneration resistors and all is good.) This amp has too many relays!
Peter
Well, I was testing it, and mechanically it a PITA so I had unmounted the 4 output tr.
I wasn't paying attention and I cooked all four. Didn't realize they bias current was that high.
Anyways, in my depressed state I noticed that the amp uses a common upc1237 protection IC.
Further checking, I think the amp's power transistors are wired as common emitter. The tr's emitters go to the power rails and the collectors are tied together and go to the relay.
Most amps seem to have a common collector topology so I started to wonder why would this amp use the less common topology ?
I thought that the output impedance of the common emitter would be higher and have less damping.
IN a couple days I should have some replace tr's and the upc1237 should come in a few weeks.
I took a spare power amp, and using un processed sub ch signal from my avr to drive the woofer for now. Its a hack but I missed the bass.
P
I wasn't paying attention and I cooked all four. Didn't realize they bias current was that high.
Anyways, in my depressed state I noticed that the amp uses a common upc1237 protection IC.
Further checking, I think the amp's power transistors are wired as common emitter. The tr's emitters go to the power rails and the collectors are tied together and go to the relay.
Most amps seem to have a common collector topology so I started to wonder why would this amp use the less common topology ?
I thought that the output impedance of the common emitter would be higher and have less damping.
IN a couple days I should have some replace tr's and the upc1237 should come in a few weeks.
I took a spare power amp, and using un processed sub ch signal from my avr to drive the woofer for now. Its a hack but I missed the bass.
P
if you had any pictures, sometimes its easier to figure out who else may have made it for Dynaudio. This was a common thing back in the day.
Profiguy:
Good point. There aren't too many markings on the board. There is at least 1 model number reference. When I get home tonight I will try to take a few pictures and post them. Thank you for the good idea.
Got the replacement tr's last night.
P
Good point. There aren't too many markings on the board. There is at least 1 model number reference. When I get home tonight I will try to take a few pictures and post them. Thank you for the good idea.
Got the replacement tr's last night.
P
![DSC_3257[1].JPG](/community/data/attachments/1082/1082684-98a7bc964f12c5e4c3256b0a3fd9bcc9.jpg?hash=mKe8lk8Sxe)
![DSC_3256[1].JPG](/community/data/attachments/1082/1082685-3eadd1ee1110c5bb20c26216fa93ef08.jpg?hash=Pq3R7hEQxb)
I managed to find a schematic for a Dynaudio BX30 and it also uses a similar CE pushpull output topology.
I also checked the 4 heat sunk driver transistors and their junctions seem fine.
P
I also checked the 4 heat sunk driver transistors and their junctions seem fine.
P
errata: the 4 output transistors are unsoldered in the picture.
1 filter cap died( initiated the problem), didn't have a plug in replacement so 4 2200uF caps are wired temporarily out of view
upc1237 protector was removed and an inline socket soldered in, and then the upc1237 was plugged in.
p
1 filter cap died( initiated the problem), didn't have a plug in replacement so 4 2200uF caps are wired temporarily out of view
upc1237 protector was removed and an inline socket soldered in, and then the upc1237 was plugged in.
p
In the attached schematic of the BX30, if the 4 output transistors are removed( 2SA1302 and 2SC3281), can the amp be safely powered up and the driver stages checked ? Not really thinking it through, I think it might be safe? If yes, then it would make trouble shooting the Sub500 amp easier.
P
P
Update 230519: replaced the 4 output tr's 2SA1943 and 2SC5200 ( 2 parallel each)
Put a DC blocking cap on the output for safety, by-passed the speaker relay. Amp seems to work.
Haven't run it for more than 30 seconds. Seems ok. Nothing got warm nor smelly.
May be I should now double check the upc1237 to see if the output relay is being activated.
P
Put a DC blocking cap on the output for safety, by-passed the speaker relay. Amp seems to work.
Haven't run it for more than 30 seconds. Seems ok. Nothing got warm nor smelly.
May be I should now double check the upc1237 to see if the output relay is being activated.
P
I took out the jumper around the speaker relay, and it seems the the upc1237 was working now. I had changed several of the electrolytics around the IC. They were all down about 25% in capacity. I tried to install the amp back into the speaker cabinet and it worked for a few minutes and then stopped. I couldn't get it to work again, so I put the amp back on the work bench. It seems the amp is fine but the upc1237 won't close the relay. I guess that the upc1237 is flakey or temperamental. I will just have to wait until the upc1237 arrives in the mail in the next few weeks.
Fixed. Last night I was double checking the off and on states of the amplifier while monitoring voltages at pins 1~ 8 of the upc1237.
All seemed good. I then checked the voltage at pin 6 of the upc1237 and that at the speaker protection relay windings and its output contacts.
Since it is a 24V relay being operated at ~ +50V, I can't just look at the voltage at pin6 but also the voltage across the coil. ( there is also a series resistor in circuit)
Since there are 4 relays in the amp, its hard to confidently know which relay is switching. It now seems that the JQX-115F -24-1HS1 relay was bad.
Between last friday and today, i had replaced all the caps connected to the upc1237. 3 caps were about at half their marked value and one cap went down to 1200pF. Perhaps that fixed the previous lack of relay drive. Now that the relay drive was there, I had to remove the relay. Once removed I cut the relay case top off. The relay contacts were good but the relay even when energized with 24V would not consistently move the contacts. I found a different form factor relay and the amp now works.
I wish in retrospect that I had more carefully checked the protection circuit.
Bad caps and a bad relay.
So far cost is 800 yen in tr's(4), bought some upc1237 from Feebay( $3USD) and some replacement relays $4USD).
~ $14.00 in parts to fix it but actually should be $4.00
+ ~ 15 hours of tinkering over the past month ( potentially very expensive)
- learning experience.= happiness
So the net experience is that electrolytics go bad and so do anything mechanical, well in this case an electromechanical relay.
P
All seemed good. I then checked the voltage at pin 6 of the upc1237 and that at the speaker protection relay windings and its output contacts.
Since it is a 24V relay being operated at ~ +50V, I can't just look at the voltage at pin6 but also the voltage across the coil. ( there is also a series resistor in circuit)
Since there are 4 relays in the amp, its hard to confidently know which relay is switching. It now seems that the JQX-115F -24-1HS1 relay was bad.
Between last friday and today, i had replaced all the caps connected to the upc1237. 3 caps were about at half their marked value and one cap went down to 1200pF. Perhaps that fixed the previous lack of relay drive. Now that the relay drive was there, I had to remove the relay. Once removed I cut the relay case top off. The relay contacts were good but the relay even when energized with 24V would not consistently move the contacts. I found a different form factor relay and the amp now works.
I wish in retrospect that I had more carefully checked the protection circuit.
Bad caps and a bad relay.
So far cost is 800 yen in tr's(4), bought some upc1237 from Feebay( $3USD) and some replacement relays $4USD).
~ $14.00 in parts to fix it but actually should be $4.00
+ ~ 15 hours of tinkering over the past month ( potentially very expensive)
- learning experience.= happiness
So the net experience is that electrolytics go bad and so do anything mechanical, well in this case an electromechanical relay.
P
errata:
ordered a replacement 10,000uF @ 100V 105C cap( it may have been the originator of the cascade of failures)
Original PS cap was a 80V part
P
ordered a replacement 10,000uF @ 100V 105C cap( it may have been the originator of the cascade of failures)
Original PS cap was a 80V part
P
replacement cap had the wrong lead pitch but it fit with some 12gauge jumpers. The replacement output protection relay arrived yesterday. The amp is bolted back into the sub and all seems good. For those with one of these amps: trouble shooting hints, check the main caps, caps around the protection IC(upc1237), and the speaker output relay.
P
P
The Dynaudio sub died again. No power to the power amp. I thought it was the upc1237 issue or a relay again. Since I had previously put a socket in for the upc1237, I spent last night making an extension jig, see pic ..6906 I checked all the pins for the correct levels. No issue when I forced the power relay on.
It turns out that there are two tiny slide switches next to the flexible cable connector. The lower switch was not slid far enough to make contact. I guess at one time there was nail polish on it to prevent it from sliding but its flaked off. So if you suddenly find that the unit doesn't power on, check the two yellow switches.
I reassembled, and then realized I didn't put nail polish on the switches!
Ugh
P
It turns out that there are two tiny slide switches next to the flexible cable connector. The lower switch was not slid far enough to make contact. I guess at one time there was nail polish on it to prevent it from sliding but its flaked off. So if you suddenly find that the unit doesn't power on, check the two yellow switches.
I reassembled, and then realized I didn't put nail polish on the switches!
Ugh
P
