Hi all,
Noobie here. I tried to establish if this is the correct sub forum is the right place to ask this question but I'm still unsure! So my apologies in advance.
I bought a Technics SU A700 mk3 amplifier along with some other separates over 20 years ago. I worked and saved really hard at the time to buy this setup. It's been really good to me. It's been sat in the same spot for the last 10 years and worked find until around 4 years ago when it just would not switch on. I was too nervous to actually open it up and see what the problem was with it being an electrical item - that shows how much I know!
So it's been sat for a length of time and I have been unable to enjoy it. The other week I tried googling why it might not work and found a video where I could see inside (wish I'd done this sooner!). So I opened it up and found a blown fuse where the power supply cable plugs in. Kicking myself thinking 'is that all that's wrong?' I googled the fuses and bought a pack of 10.
I installed the fuse and it blew straight away 😕 I tried another and the problem is consistent. So I thought I'd replace another and do some more googling and found this great place!
I've taken some pics. If anyone has experience of this error, or can point me in the right direction with simple talk of what could be wrong / what to try that would be brilliant. I would love to get it back up and running.
Many thanks
Noobie here. I tried to establish if this is the correct sub forum is the right place to ask this question but I'm still unsure! So my apologies in advance.
I bought a Technics SU A700 mk3 amplifier along with some other separates over 20 years ago. I worked and saved really hard at the time to buy this setup. It's been really good to me. It's been sat in the same spot for the last 10 years and worked find until around 4 years ago when it just would not switch on. I was too nervous to actually open it up and see what the problem was with it being an electrical item - that shows how much I know!
So it's been sat for a length of time and I have been unable to enjoy it. The other week I tried googling why it might not work and found a video where I could see inside (wish I'd done this sooner!). So I opened it up and found a blown fuse where the power supply cable plugs in. Kicking myself thinking 'is that all that's wrong?' I googled the fuses and bought a pack of 10.
I installed the fuse and it blew straight away 😕 I tried another and the problem is consistent. So I thought I'd replace another and do some more googling and found this great place!
I've taken some pics. If anyone has experience of this error, or can point me in the right direction with simple talk of what could be wrong / what to try that would be brilliant. I would love to get it back up and running.
Many thanks
If that is the only fuse in the unit and by the looks of it it is connected to the mains input and not the output devices I would suspect that the primary of the mains transformer is short circuit in the winding's .
That is the first port of call before I would start checking the power supply components.
Okay disconnect the secondary winding's from the rectifier then replace fuse and see if that blows .
That is the first port of call before I would start checking the power supply components.
Okay disconnect the secondary winding's from the rectifier then replace fuse and see if that blows .
Because the fuse blows right away, indicates a short somewhere. The most likely area is the power supply or possibly the output devices. This amplifier uses a pair of large scale integrated circuits (LSIC). These are the two black things connected to the heat sink. To eliminate the possibility of a shorted power transformer, unplug the white connector cable running from the transformer circuit board (green) to the main board (brown). There should be a disconnect at the brown board. Then replace the fuse and try turning it on. If the fuse stays ok your problem in on the main board. If it blows there are 4 rectifier diodes on the small green board that could also cause it. Otherwise it may be the transformer.
There are 4 larger power supply diodes on the main (brown) board near the two standing black capacitors that must be checked. You will need a decent multimeter to check these. Lacking that, there is little more you can do yourself.
Also, to save on fuses, a series light bulb tester is very handy. This means putting an incandescent lamp (60 to 100Ws) in series with the AC line. This is something you make yourself.
(Link to manual)
(dim-bulb-tester)
There are 4 larger power supply diodes on the main (brown) board near the two standing black capacitors that must be checked. You will need a decent multimeter to check these. Lacking that, there is little more you can do yourself.
Also, to save on fuses, a series light bulb tester is very handy. This means putting an incandescent lamp (60 to 100Ws) in series with the AC line. This is something you make yourself.
(Link to manual)
(dim-bulb-tester)
Attachments
Last edited:
rkuk,
You are welcome to the Tubes / Valves part of the diyAudio Forum.
It seems that this is the favorite site for all kinds of amplifier questions on the diyAudio Forum.
We have lots of answers here.
There also is the Solid State part of the diyAudio Forum.
You can ask your questions there too.
The Instruments & Amps people also post their questions here on the Tubes / Valves part of the diyAudio Forum.
But Instruments & Amps are for Guitar amps, not Hi Fi / Stereo amps.
At least your amplifier qualifies as a Hi Fi or Stereo amplifier, not a Guitar amp.
I would rather have your questions posted here, instead of having Guitar amp questions posted on this part of the Forum.
Hello, is anybody out there listening, is this microphone on?
I hope the persons on the Tubes / Valves can answer your questions, and get your amp fixed and up and running.
You are welcome to the Tubes / Valves part of the diyAudio Forum.
It seems that this is the favorite site for all kinds of amplifier questions on the diyAudio Forum.
We have lots of answers here.
There also is the Solid State part of the diyAudio Forum.
You can ask your questions there too.
The Instruments & Amps people also post their questions here on the Tubes / Valves part of the diyAudio Forum.
But Instruments & Amps are for Guitar amps, not Hi Fi / Stereo amps.
At least your amplifier qualifies as a Hi Fi or Stereo amplifier, not a Guitar amp.
I would rather have your questions posted here, instead of having Guitar amp questions posted on this part of the Forum.
Hello, is anybody out there listening, is this microphone on?
I hope the persons on the Tubes / Valves can answer your questions, and get your amp fixed and up and running.
Last edited:
Hi everyone,
Thank you for the warm welcome and the help. I really appreciate your reply HollowState, as those are the kind of instructions that help me most (highlighting the colours and shapes of things! 😱).
I will try disconnecting the cable between the two circuit boards tomorrow and report back.
Unfortunately I do not own a multimeter or the parts to make the bulb tester (well possibly if I scour around in old boxes for parts when renovating), but perhaps I can buy some equipment if necessary at the next steps. At least I have 8 attempts left with fuses for now! 😱😱
Thanks.
Oh and I had a little scroll through some of the pics on this forum - whilst I don't understand a lot of it, the beauty that has gone into making some homemade projects is just amazing!!! Pieces of art! (just thought I'd share the appreciation)
Thank you for the warm welcome and the help. I really appreciate your reply HollowState, as those are the kind of instructions that help me most (highlighting the colours and shapes of things! 😱).
I will try disconnecting the cable between the two circuit boards tomorrow and report back.
Unfortunately I do not own a multimeter or the parts to make the bulb tester (well possibly if I scour around in old boxes for parts when renovating), but perhaps I can buy some equipment if necessary at the next steps. At least I have 8 attempts left with fuses for now! 😱😱
Thanks.
Oh and I had a little scroll through some of the pics on this forum - whilst I don't understand a lot of it, the beauty that has gone into making some homemade projects is just amazing!!! Pieces of art! (just thought I'd share the appreciation)
Good morning 🙂
I'm back. Rather embarrassingly 😱 ....does anyone know how to remove these connections? I thought it would be like a PC component and just pull off the board, but after gently trying that doesn't seem to be the case. Then I wondered if the little white blocks somehow clamped the cables in but they don't seem to want to move either.
I definitely don't want to just yank it out in case I break it altogether. (Yes I am this level of new!)
I'm back. Rather embarrassingly 😱 ....does anyone know how to remove these connections? I thought it would be like a PC component and just pull off the board, but after gently trying that doesn't seem to be the case. Then I wondered if the little white blocks somehow clamped the cables in but they don't seem to want to move either.
I definitely don't want to just yank it out in case I break it altogether. (Yes I am this level of new!)
I am not familiar with that particular fastener. And it has been years since I have done servicing on home equipment. I wouldn't want to miss advise you. The white pieces do look like they hold the wires in, but I'm not exactly sure how to remove them. If they are removable. You might try contacting Technics directly and try speaking with someone in the service department or a service facility recommended by them. Assuming you could get through to anyone.
But for now leave it alone.
I have also noticed, by studying the manual, that the front panel power button does not control the AC mains voltage directly. Under normal operating conditions, when the AC plug is connected to the house power, the power transformer is always seeing voltage. The front panel button activates control circuity that operates relays (blue boxes) for applying DC to the unit. It does this by connecting the transformer's secondary voltage to the main bridge rectifiers. Those 4 diodes on the main board.
So what this means is if you can just plug it in with a good fuse (power button off) and not try turning it on via the front panel button, and it doesn't blow, the transformer and control voltage diodes on the green board are good. No need to disconnect the white (ribbon) cable. But if the fuse blows when pushing the button on, then there is a short somewhere on the main board. Most likely a rectifier, capacitor or even one of the output modules on the heat sink.
The rectifiers can be checked with an ohmmeter suitable for checking diodes. There should be high resistance in one direction, and very low resistance in the other direction. Low resistance in both directions would indicate a shorted diode.
But for now leave it alone.
I have also noticed, by studying the manual, that the front panel power button does not control the AC mains voltage directly. Under normal operating conditions, when the AC plug is connected to the house power, the power transformer is always seeing voltage. The front panel button activates control circuity that operates relays (blue boxes) for applying DC to the unit. It does this by connecting the transformer's secondary voltage to the main bridge rectifiers. Those 4 diodes on the main board.
So what this means is if you can just plug it in with a good fuse (power button off) and not try turning it on via the front panel button, and it doesn't blow, the transformer and control voltage diodes on the green board are good. No need to disconnect the white (ribbon) cable. But if the fuse blows when pushing the button on, then there is a short somewhere on the main board. Most likely a rectifier, capacitor or even one of the output modules on the heat sink.
The rectifiers can be checked with an ohmmeter suitable for checking diodes. There should be high resistance in one direction, and very low resistance in the other direction. Low resistance in both directions would indicate a shorted diode.
Hello
I have a Technics SU-A700mk2 amplifier. Does somebody know the sound or any other differences between the 700mk2 and 700mk3 version? Probably the mk3 version is better, because in a Hi-Fi world when we go up towards higher models it should be better. I always wanted to know it but I never got answer to it. Thanks.
I have a Technics SU-A700mk2 amplifier. Does somebody know the sound or any other differences between the 700mk2 and 700mk3 version? Probably the mk3 version is better, because in a Hi-Fi world when we go up towards higher models it should be better. I always wanted to know it but I never got answer to it. Thanks.
karoly7603,
This All Solid State Amplifier is on the Tubes / Valves section of diyAudio.
In order to get your question answered, it might be better to Post on the Solid State section of diyAudio.
This All Solid State Amplifier is on the Tubes / Valves section of diyAudio.
In order to get your question answered, it might be better to Post on the Solid State section of diyAudio.
Last edited:
They are nearly the same,mk3 has 3ceramic capacitor added on the main board
more capacitance in smal caps in right in left channels,and more capacitance in phono section small caps.
Sounds nearly the same,maybe mk3 sounds just a little more smoother and powerfull.But listened it with exchaned main big caps to nichicon LGK KM same value
Hi rkuk,
I've got the same problem. If you managed to disconnect that white cable, can you please describe how? Also how did you end with your mk3? Thanks,
I've got the same problem. If you managed to disconnect that white cable, can you please describe how? Also how did you end with your mk3? Thanks,