I was just given an Adcom 555 MkII to see if I can repair it for a friend. The left channel is dead. I have searched thru all the 555 threads (and saw the 555 schematic) to see if anyone else has posted about a similar problem. I dont want to modify it (yet) just get it going. The B+ power supply is fine. No fuses are blown.
What are the common failures on these amps? There are also 2 IC's that I dont see on the posted schematic marked ADCOM 3A as well as 9039. I'm assuming the 555 II is similar to the 555 based on posts I have read here. Any comments or ideas appreciated.
Thanks
BL
What are the common failures on these amps? There are also 2 IC's that I dont see on the posted schematic marked ADCOM 3A as well as 9039. I'm assuming the 555 II is similar to the 555 based on posts I have read here. Any comments or ideas appreciated.
Thanks
BL
Further comments:
I have to admit I didnt search very well on this board before I posted my question. I used 555 without the II and came up with lost more information. I have now learned about the op-amps, what they do and what their replacement is. Also have the bias procedure for when I do get it fixed. The 555 does not have these IC's. I'm still poking around inside and the problem is
in/around/near the drivers. I still need a schematic for the 555II
or at least expected voltages at key points
Thanks
I have to admit I didnt search very well on this board before I posted my question. I used 555 without the II and came up with lost more information. I have now learned about the op-amps, what they do and what their replacement is. Also have the bias procedure for when I do get it fixed. The 555 does not have these IC's. I'm still poking around inside and the problem is
in/around/near the drivers. I still need a schematic for the 555II
or at least expected voltages at key points
Thanks
Need source or equivalents
I have found the bad device in the 555 II I am reparing - 2SA1210 PNP 200v 140ma
What I need is a source that will sell these in small numbers OR I need an equivalent. Having searched these forms and elsewhere they all advise to avoid NTE/ECG so the possible subs I am looking at are MJE350 2SA1540 2SA1209 2SA939S and 2SA1698.
Honestly I don't know enough to say which one is the better choice or if any of these are suitable. The failed device is Q105 on the schematic.
Adcom did e-mail me a schematic but it is almost unreadable.
I have found the bad device in the 555 II I am reparing - 2SA1210 PNP 200v 140ma
What I need is a source that will sell these in small numbers OR I need an equivalent. Having searched these forms and elsewhere they all advise to avoid NTE/ECG so the possible subs I am looking at are MJE350 2SA1540 2SA1209 2SA939S and 2SA1698.
Honestly I don't know enough to say which one is the better choice or if any of these are suitable. The failed device is Q105 on the schematic.
Adcom did e-mail me a schematic but it is almost unreadable.
If you replace ALL of the drivers with the same type of matched pairs (pnp+npn, don't replace only the pnps), you should choose the couple that has these characteristics: (in order of importance)
- max Ic
- max Vce
- DC hfe
- if you can, even the frequency response
(obvius, don't take RF or switching units)
And if you can, buy the same case style of the originals. That will help with the pinout and the appearance.
I have a Marantz 1060 that has the same problems, and the only matched pair I could get was a T0126, not the beautiful T05 metal can like the originals. Obviusly the pinout was different, and I had to stretch the pins in the right places. Obviusly a pin broked just out of the plastic box, and I tried to resolder it. It looked well, but when I plugged the unit and turned the power on it burned a bunch of components.
- max Ic
- max Vce
- DC hfe
- if you can, even the frequency response
(obvius, don't take RF or switching units)
And if you can, buy the same case style of the originals. That will help with the pinout and the appearance.
I have a Marantz 1060 that has the same problems, and the only matched pair I could get was a T0126, not the beautiful T05 metal can like the originals. Obviusly the pinout was different, and I had to stretch the pins in the right places. Obviusly a pin broked just out of the plastic box, and I tried to resolder it. It looked well, but when I plugged the unit and turned the power on it burned a bunch of components.
Getting back to look at this thing again after the holidays. Since this is not my amp and am repairing it for a friend, He contacted ADCOM and they mailed him 2SA1380/2SC3502 as subs for the
2SA1210/2SC2912. Sanyo datasheet shows these as "Ultrahigh Definition CTR Display,Video Output Applications". Max Ic is less than the originals..are these suitable? Thanks BL
2SA1210/2SC2912. Sanyo datasheet shows these as "Ultrahigh Definition CTR Display,Video Output Applications". Max Ic is less than the originals..are these suitable? Thanks BL
Bah, if Adcom says they're right....
What are the Icmax ratings of the originals and the new ones?
What are the Icmax ratings of the originals and the new ones?
I cant find a datasheet for the 2SA1210. The 1209 is rated at 140ma and the 1208 at 70ma so I'm thinking the 1210 is higher than 140ma. The 2SA1380 is rated at 100ma.
BL
BL
Go ahead and try them, jus have a 100 watt bulb in series with the AC fuse so that there are no "KABOOMS" 😀
Also see if any of the outputs are shorted out. I have never repaired an Adcom whose outputs were fine....
Also check all diodes especially the zeners, those have a tendancy to fail.
I have original Adcom 555II drivers and outputs if you need them. Email me. I might even have the A1210. email me... too lazy to do to the basement and check.
Also see if any of the outputs are shorted out. I have never repaired an Adcom whose outputs were fine....
Also check all diodes especially the zeners, those have a tendancy to fail.
I have original Adcom 555II drivers and outputs if you need them. Email me. I might even have the A1210. email me... too lazy to do to the basement and check.
Thanks for the information. I do intend to use a lightbulb on power-up
(after reading about that on here) The diodes have been checked and are OK. Only Q5 was found to be bad and I dont know why it blew. The outputs are not shorted at the binding posts so I think the output trannies are OK. I'll let you know if I need your parts.
BL
(after reading about that on here) The diodes have been checked and are OK. Only Q5 was found to be bad and I dont know why it blew. The outputs are not shorted at the binding posts so I think the output trannies are OK. I'll let you know if I need your parts.
BL
Thanks to all who replied to my original posts. The amp was powered up with the lightbulb. The amp "sort-a" came up, just enough to know everything was OK. Then I brought it up on full AC. Biased it and ran it for a few days then biased it again. It has been back in service since January and used daily. I got a call last night, it has blown (same channel) and taken out the woofer with it this time. I dont have it back here yet to look at but have been told there is 90VDC on the output. Any ideas what could have happened and what to look at when I do get it back? In the original failure there was no DC on the outputs (and 90V is more then the B+). BL
computeruser said:
90v at output means it was run with a variac cranked up to: 130vac or he has bad voltages. 90v will take out the Adcom OP stage if operated below 8 ohms.... If fuses are intact, maybe the driver is blown again.... make sure the next level drivers are not shorted b to E... meaning they will be driving the OP stage and burn out....
Can't say but 90 v is 6-7% over spec....
Sorry maybe I was not clear...amp was not on Variac when it blew this time. Amp was repaired and returned to service in January and had run fine until this week. This time the left B- rail fuse blew and the owner (I'm not a shop - this person is a friend) replaced it with a new 7A fuse. Same thing and owner assumed it was the fuse again (and called me). I got down there today to look at it. The DC rails ARE around 80VDC. The second fuse (the one the owner put in to replace the blown one and is still in the amp) looked like it was starting to blow but this time his speakers must have taken the hit so the fuse didnt have to blow. There is 90VDC at the left output. When I repaired the amp back in January I removed and tested all the transistors. Only Q105 was bad. I replaced (on both channels):
C202/C302 C252/C352 C109/C159/C104/C154
R108/R158 / R110/R160
D101/D02 D151/D152
IC101/IC151 - (Adcom 3A replaced by AD820)
J101/J151 new terminal blocks & plugs on cables (the old ones were brittle and broken)
Semiconductors Replaced:
Q105/Q155 2SA1210 with 2SA1380
Q107/Q157 2SA1210 with 2SA1380
Q108/Q158 2SC2912 with 2SC3502
All on the input/driver board. I tested the transistors on the heatsinks (they were all OK) They may still be OK. When the amp is off, the left outputs at the binding posts are not shorted or open and measure the same as the good (right) channel.
I'm just wondering where to start looking this time (I still dont have the amp on the bench yet) as there are so many people on here who know these amps.
Thanks
BL
C202/C302 C252/C352 C109/C159/C104/C154
R108/R158 / R110/R160
D101/D02 D151/D152
IC101/IC151 - (Adcom 3A replaced by AD820)
J101/J151 new terminal blocks & plugs on cables (the old ones were brittle and broken)
Semiconductors Replaced:
Q105/Q155 2SA1210 with 2SA1380
Q107/Q157 2SA1210 with 2SA1380
Q108/Q158 2SC2912 with 2SC3502
All on the input/driver board. I tested the transistors on the heatsinks (they were all OK) They may still be OK. When the amp is off, the left outputs at the binding posts are not shorted or open and measure the same as the good (right) channel.
I'm just wondering where to start looking this time (I still dont have the amp on the bench yet) as there are so many people on here who know these amps.
Thanks
BL
Hi computeruser,
Start by testing the outputs and drivers for leakage and gain. Remount with fresh heatsink grease (after cleaning the old off) and new mica insulators. Take your time and work carefully. Replace transistors to one stage back of any failed transistor. Do not even dream of using ECG or NTE devices.
Changing the Adcom 3A op amps was not necessary. THey are not in the signal path, just a DC servo.
Check the resistance from the input jack to ground. If this blows it may cause problems for you.
I know this is a fair amount of work, but speakers are expensive.
-Chris
Start by testing the outputs and drivers for leakage and gain. Remount with fresh heatsink grease (after cleaning the old off) and new mica insulators. Take your time and work carefully. Replace transistors to one stage back of any failed transistor. Do not even dream of using ECG or NTE devices.
Changing the Adcom 3A op amps was not necessary. THey are not in the signal path, just a DC servo.
Check the resistance from the input jack to ground. If this blows it may cause problems for you.
I know this is a fair amount of work, but speakers are expensive.
-Chris
He keeps bringing up the 90v and that is worrisome!
Take out all DC fuses and powered up measure voltages on EACH power cap. PLease report back.
Take out all DC fuses and powered up measure voltages on EACH power cap. PLease report back.
Hi K-amps,
I don't find a reference to supply voltages but 80V seems right. An open ground will give asymetric supplies. So ... good point.
computeruser,
Where are you grounding your meter for readings? Are both supply voltages the same but opposite in polarity? Please let us know when you have the amp back on your bench.
-Chris
I don't find a reference to supply voltages but 80V seems right. An open ground will give asymetric supplies. So ... good point.
computeruser,
Where are you grounding your meter for readings? Are both supply voltages the same but opposite in polarity? Please let us know when you have the amp back on your bench.
-Chris
Chris... I have worked with 555ii's a lot. The normal rails are 83-84vdc. 90v it way too high, Even the GFA5802 is only 87v.
I haven't worked on THAT many of them, but even on the half-dozen I've seen, two had the output of the stock opamp stuck at a rail. I got a few AD820's to use as a replacment at the suggestion of someone, and offset never creeps above 0.2mV with them in place, wheras before, IIRC, a millivolt or two was not uncommon. So...audible or not, the 820 makes a nice substitute.
I only have the schematic for the 555II, but the voltage rails are not given. Bummer. But 90V sounds pretty excessive.
K-amps,
Yup, I am agreeing with you. I work on so many amps I don't trust my memory unless the voltage is marked or I have one to measure in front of me. Don't forget I did warranty on them for years so they kind of blend together for details like supply voltages.
EchoWars,
2mV, 0.2mV. Not enough to worry about changing the op amps for. No complaint with the type, I'm just questioning the motive or advice to replace them. One of those "if they ain't broke, don't fix them" things. Now, if they were defective you may as well use the better part.
I'm just waiting to find out if there is a broken ground reference that might cause a DC offset at the output or some other weird fault.
-Chris
Yup, I am agreeing with you. I work on so many amps I don't trust my memory unless the voltage is marked or I have one to measure in front of me. Don't forget I did warranty on them for years so they kind of blend together for details like supply voltages.
EchoWars,
2mV, 0.2mV. Not enough to worry about changing the op amps for. No complaint with the type, I'm just questioning the motive or advice to replace them. One of those "if they ain't broke, don't fix them" things. Now, if they were defective you may as well use the better part.
I'm just waiting to find out if there is a broken ground reference that might cause a DC offset at the output or some other weird fault.
-Chris
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