Hello Everyone!
Having a bit of an issue with my old faithful TEAC H500 AMp
The manual source selection on this old Amp has stopped working...it uses an ALPS encoder switch to increment 'Up or Down' signal.
Im confident the encoder switch is not it...checked with meter..and also had a spare ALPS Encoder which I swapped in/out and made no difference.
The thing with this is that using a Remote Control to change source input still works fine...source selection is highlighted by an LED and that works also.
Any thoughts from anyone appreciated..it would be nice to have this Amp completely working.
Seen a couple of people have had selector issues...but no luck...if anyone can help ..any thoughts would be most appreciated. Thankyou.
Having a bit of an issue with my old faithful TEAC H500 AMp
The manual source selection on this old Amp has stopped working...it uses an ALPS encoder switch to increment 'Up or Down' signal.
Im confident the encoder switch is not it...checked with meter..and also had a spare ALPS Encoder which I swapped in/out and made no difference.
The thing with this is that using a Remote Control to change source input still works fine...source selection is highlighted by an LED and that works also.
Any thoughts from anyone appreciated..it would be nice to have this Amp completely working.
Seen a couple of people have had selector issues...but no luck...if anyone can help ..any thoughts would be most appreciated. Thankyou.
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The function selector SW72 has 3 connection pins, 1 pin to the ground, the other 2 pins direct go to the MCU pin33 pin34 which have around 4.7V on these 2 pins.
Please check the PCB traces for these 2 connections to MCU pin33 pin34, if there is no broken trace and the switch is good then it will be the MCU internal problem and it can not be repaired except change the MCU.
Please check the PCB traces for these 2 connections to MCU pin33 pin34, if there is no broken trace and the switch is good then it will be the MCU internal problem and it can not be repaired except change the MCU.
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Hello Patrick101
Many thanks for your reply and helpful post!
Ive tested and found 4.7volts at both pin33 and pin34 at the same time....so I guess we can assume it must be the MCU that is at fault!?.
Resistance between Pin33 and Pin 34 on the MCU (without the encoder switch installed) is about 9megohm.
Unfortunately these MCU chips seem to be made by Anam Korea and impossible to find much info or find any to replace.
Im lucky input selection is still functional via remote control at the moment.
Perhaps I might get lucky and find a unit in time that I could use for spares.
Cheers
Just a final thought about this manual input selector issue...as it is it looks-like to be a fault on the MCU IC pins 33 and pin 35 (not 34 as I prev stated)
As the remote control input selection still works...so to add a manual selection option again (without finding and changing the current faulty MCU IC) then if I were bored perhaps could make up an Arduino with a rotary switch and IR transmitter..learning the remote codes for input selection and transmitting them with each selection of the rotary switch...mounting the circuit internally and rotary switch in place of the current encoder switch...just a thought to how to make it appear all working as such!
The reality is....thought is easier than doing...and its easy enough for now to hit the remote input select!
Cheers
As the remote control input selection still works...so to add a manual selection option again (without finding and changing the current faulty MCU IC) then if I were bored perhaps could make up an Arduino with a rotary switch and IR transmitter..learning the remote codes for input selection and transmitting them with each selection of the rotary switch...mounting the circuit internally and rotary switch in place of the current encoder switch...just a thought to how to make it appear all working as such!
The reality is....thought is easier than doing...and its easy enough for now to hit the remote input select!
Cheers
I guess replacing the ALPS encoder is an old school idea? I mean, these break down and are simple to replace. You can burn your time with an Arduino if you like but I would first use the simple solution 🙂
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Yes your right... I tried another ALPS encoder switch with same result...The Arduino idea...its just a thought and it would take a fair effort.
I still will look out for a unit for spares..and ultimately swap a board or IC if I get one.
You already did try a new encoder of the same type? Ha I see, I overread that.
C711 and C712 are both measured and found to be OK?
C711 and C712 are both measured and found to be OK?
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Hello Jean-Paul
Thanks for your reply
Ive got the amp apart still and will test the two caps fully tomorrow.
Will report back.
Cheers
Hello Jean Paul
I removed both C711 and C712 ..tested with an MTester LCR
..results 75000pF and 80000pF...so probably ok?!
Although the tester is showing them a little higher values than the expected 68000pF... Im guessing we are close enough though and it does make the MCU IC look more like the issue.
I might see if I can get a couple of new caps and change them anyway before reassembling the Amp.
Cheers
They seem OK, it was the last try I guess. The IC will be a hard one to find and also hard to replace...
Yes thanks Jean Paul your right.....Its a South Korean 'Anam' made unit with proprietary IC''s..not available..I think my best hope is to find another unit on ebay or such which is faulty for another reason!
Or if not and I get (very) bored I could have a go at the micro sized arduino Rotary Switch to IR transmitter as mentioned 🙂
For now I will replace the caps and reassemble...luckily its still sounds great !
Cheers
This kind of failure is frustrating as it is a one way direction to the landfill in many cases. Apparently this Anam IC is made with a built-in weakness.
Thanks Jean Paul...Yes agree it is frustrating.... we do our best to keep units out of landfill...luckily I can still use this unit for now...but guess the chip may fail completely..so will keep looking out for a spare unit.
Cheers and Thanks !
You don't happen to have a dual channel scope to take a look at what's going on at pins 33 and 35 when the encoder is rotated? I guess even a multimeter would be better than nothing if you take it s-l-o-w. I'd want to see the correct kind of pulses before condemning the microcontroller... it could still be a bad trace or lifted pad causing a bad ground at the encoder or something.
Thanks Sgrossklass for your reply
What I will do is get a couple of replacement (Encoder) Caps for C711 C712 and then look with the scope..I agree it would be interesting to see what is happening with the scope at pin33 and pin 35 for sure.
I did try a replacement ALPS encoder (same result) used this model :
EC12 Series - Basic information
The replacement encoder was not physically the same size but I believe it matches in operable specification.
Will report back with results!
Cheers
Oscilloscope testing on pins 33 and 34...tells me the original ALPS Encoder is fine...and tracks are fine up to the MCU Pins....it must be the therefore the MCU IC unfortunately...you could see with the Scope Switching of both Encoder Channels 'A and B' in sequence as you rotate the Encoder as expected... Reassembled Amp for now and will continue to use it ...all the while will keep an eye out for a spares unit.
Cheers
Cheers