Bert 1100
Super Member
I couldn't resist buying this not-so-little Technics integrated from 1976 - 1977. I knew there was no sound from one channel and the power switch had been bypassed...
If you've seen this already, it's because I posted a few pics in the"Show us your Technics stuff !" thread
This rebuild all happened about a month ago while I had a week off from work...
What decided me was the good looks, the build quality, the bypassable tone controls and the load-adustable phono pre.
It is really nicely built and is very easy to work on since it has plug-in power amp boards (one for each channel) and also plug in tone boards (also one for each channel)
The power supply is really well thought out and robust. The main rails are fed from 2 10'000uf 50V caps (a lot for a 2x40 watt amp !)
There are plenty of biggish local filter caps.
The secondary power supply comes from separate windings and is a regulated + / - 40VDC, adjustable.
The dc offset is adjustable, as well as the idle current of course. the pots are easily accessible on top of the amp cards.
The protection system is quite different from similar amps of other manufacturers :
The relay passes the main AC rails to the rectifier as long as all is well. The normal state of the relay is with closed contacts. So don't expect a click after power-up.
If you hear a click it means there is something wrong and power to the amp cards has been cut off (before even the rectifier...)
So, at first power-up, my relay clicks, but no sound at all. Ok....
I soon figured out the relay was NOT supposed to click.
So I start diagnosis.....and soon find out that with the left amp board out, I get good sound from the right channel.
Problem isolated to the left channel amp board....I started this thread to get some help.
I pulled ALL semiconductors to test them, they all were fine although the diff pair (two 2sa640) had an Hfe of 185 and 95.
But that was not my problem, I swapped them with matched ksa992 with no difference.
So I started checking trace continuity and found a broken trace ! Nothing visible at all, but zero continuity !
So, that was bridged with a wire and all was working well !
I also started a thread about the broken power switch, and thanks to Gort69 I found a switch that was close enough. On the left the new, in the middle the new modified, on the right the broken original.
So I started with the full rebuild :
the power boards got new diff pair transistors. The originals were 2sa640, changed for KSA992.
the pinout is the same, but the originals were facing away from each other and were not temperature coupled.
So the new transistors got some leg-bending and are now together in shrink-wrap.
I swapped the original electrolytic 0.68uf input coupling cap for a Mundorf film (the cheaper ones)
The phono pre got all new electrolytics, two tantalums and two small lytics were changed for Wima MKS2.
The main board : all new lytics (mostly Silmic II but a few Nichicons as well), new relay, new soft/fast recovery diodes for the secondary PS.
Also some small lytics replaced by Wima MKS2
The tone boards got all new lytics (one BP Muse in each board) and again some small lytics replaced by Wima MKS2.
To be followed in the next post...
If you've seen this already, it's because I posted a few pics in the"Show us your Technics stuff !" thread
This rebuild all happened about a month ago while I had a week off from work...
What decided me was the good looks, the build quality, the bypassable tone controls and the load-adustable phono pre.
It is really nicely built and is very easy to work on since it has plug-in power amp boards (one for each channel) and also plug in tone boards (also one for each channel)
The power supply is really well thought out and robust. The main rails are fed from 2 10'000uf 50V caps (a lot for a 2x40 watt amp !)
There are plenty of biggish local filter caps.
The secondary power supply comes from separate windings and is a regulated + / - 40VDC, adjustable.
The dc offset is adjustable, as well as the idle current of course. the pots are easily accessible on top of the amp cards.
The protection system is quite different from similar amps of other manufacturers :
The relay passes the main AC rails to the rectifier as long as all is well. The normal state of the relay is with closed contacts. So don't expect a click after power-up.
If you hear a click it means there is something wrong and power to the amp cards has been cut off (before even the rectifier...)
So, at first power-up, my relay clicks, but no sound at all. Ok....
I soon figured out the relay was NOT supposed to click.
So I start diagnosis.....and soon find out that with the left amp board out, I get good sound from the right channel.
Problem isolated to the left channel amp board....I started this thread to get some help.
I pulled ALL semiconductors to test them, they all were fine although the diff pair (two 2sa640) had an Hfe of 185 and 95.
But that was not my problem, I swapped them with matched ksa992 with no difference.
So I started checking trace continuity and found a broken trace ! Nothing visible at all, but zero continuity !
So, that was bridged with a wire and all was working well !
I also started a thread about the broken power switch, and thanks to Gort69 I found a switch that was close enough. On the left the new, in the middle the new modified, on the right the broken original.
So I started with the full rebuild :
the power boards got new diff pair transistors. The originals were 2sa640, changed for KSA992.
the pinout is the same, but the originals were facing away from each other and were not temperature coupled.
So the new transistors got some leg-bending and are now together in shrink-wrap.
I swapped the original electrolytic 0.68uf input coupling cap for a Mundorf film (the cheaper ones)
The phono pre got all new electrolytics, two tantalums and two small lytics were changed for Wima MKS2.
The main board : all new lytics (mostly Silmic II but a few Nichicons as well), new relay, new soft/fast recovery diodes for the secondary PS.
Also some small lytics replaced by Wima MKS2
The tone boards got all new lytics (one BP Muse in each board) and again some small lytics replaced by Wima MKS2.
To be followed in the next post...
Last edited:
