Hi everyone, I'm Roberto from northern Italy. I'm interested in electronics and sometimes I have fun repairing vintage amplifiers and turntables.
I'm in a very deep black hole with a Goldmund PL-7 speed controller that doesn't work yet.
Someone knows where I can find a service manual for this board? It belongs to a Goldmund Reference 1 equipped with a T3F tonearms.
I started with the missing cable connecting the PL-7 and the tonearm.....making a new cable and changing the connectors on the two sides because it's very difficult to find the originals connectors. The tone arm is working, the motor of the TT is working and applying the correct power supply directly to the synchronous 24V AC motor I can play a 33 turns LP.
After some months spent try to understand the mother board of the PL-7 (I've reversed engineered quite all the board) I'm quite sure that the problem is in the logic that control the power section of the board.
I can't understand if there is a problem in the Eprom (lost the program?) or in the microprocessor (Motorola M6800P) or in the I/O module of the 6800 (6840).
It seems that the board isn't yet able to understand the inputs from the buttons (only the POWER button is still working but it's involved in the electromechanics).
The logic don't feed the third grade Butterworth filter with the square wave and nothing come out from this IC.
The electronics feed the M6800P with the two correct clocks, by the way one of these two is not so good.
Thank you for any suggestions
I
I'm in a very deep black hole with a Goldmund PL-7 speed controller that doesn't work yet.
Someone knows where I can find a service manual for this board? It belongs to a Goldmund Reference 1 equipped with a T3F tonearms.
I started with the missing cable connecting the PL-7 and the tonearm.....making a new cable and changing the connectors on the two sides because it's very difficult to find the originals connectors. The tone arm is working, the motor of the TT is working and applying the correct power supply directly to the synchronous 24V AC motor I can play a 33 turns LP.
After some months spent try to understand the mother board of the PL-7 (I've reversed engineered quite all the board) I'm quite sure that the problem is in the logic that control the power section of the board.
I can't understand if there is a problem in the Eprom (lost the program?) or in the microprocessor (Motorola M6800P) or in the I/O module of the 6800 (6840).
It seems that the board isn't yet able to understand the inputs from the buttons (only the POWER button is still working but it's involved in the electromechanics).
The logic don't feed the third grade Butterworth filter with the square wave and nothing come out from this IC.
The electronics feed the M6800P with the two correct clocks, by the way one of these two is not so good.
Thank you for any suggestions
I
Hi Ganther, many thanks. Here, I hope, you can see the board of the motor controller:
It seems I have downsized too many, sorry....
All you can see at the right of the big relay down it's the power section. I have replaced all the electrolitic caps and all the ceramic caps all over the board (apparently some of them was bad)
Same for the linear power supply for the logic (7805), the power opamp (dual supply), the TIP111 and 112 power transistor you can see at the right down corner
I can't read the eprom I haven't the right reader and a new one it's really too expensive for a one shoot use
It seems I have downsized too many, sorry....
All you can see at the right of the big relay down it's the power section. I have replaced all the electrolitic caps and all the ceramic caps all over the board (apparently some of them was bad)
Same for the linear power supply for the logic (7805), the power opamp (dual supply), the TIP111 and 112 power transistor you can see at the right down corner
I can't read the eprom I haven't the right reader and a new one it's really too expensive for a one shoot use
I haven't the schematics and I'm searching for it, but I checked the signals coming out from the MC6875:
phi1 and phi2 are the same I can find on the MC6800P. The MCU is also generating the E (enable) signal for the EF6821 that's the peripheral interface adapter for the MC6800P. It seems that Reset Ouput and Power On Reset aren't used and connected to ground
phi1 and phi2 are the same I can find on the MC6800P. The MCU is also generating the E (enable) signal for the EF6821 that's the peripheral interface adapter for the MC6800P. It seems that Reset Ouput and Power On Reset aren't used and connected to ground
Here I checked the inputs to the EF6821: the E (enable) is clocking right, when I press the 33 button after some bouncing the signal (tasto 33) goes low but I don't understand why it doesn't return high. There's only a kind of pull up resistor between the contact of the button 33 and the input of the EF6821.
When you don't press the button the input is set to high when you push goes low but after that it would be high. Moreover I'm seeing a very dirty signal on the input tasto 45 and it goes low but I never press the button 45
MC6875 is the clock generator for the MC6800. Clock is two non overlappin phases : Ph1 by Ph2.
E : Is Enable pin of the PIA (6821) this has to be Ph2 which is the main clock used by the 68xx and 65xx peripherals.
Whats matters is reset pin of the CPU. Could you check cpu pin40 with analyser. If low there's something wrong with reset and fact that Power On Reset (p12) on 6875 is low it not a good sign.
E : Is Enable pin of the PIA (6821) this has to be Ph2 which is the main clock used by the 68xx and 65xx peripherals.
Whats matters is reset pin of the CPU. Could you check cpu pin40 with analyser. If low there's something wrong with reset and fact that Power On Reset (p12) on 6875 is low it not a good sign.
Just saw you last post and the strange E waveform between 50 and 50us. E (Ph2) should never stop except if cpu is suspended to allow access for slow devices, wihich is usually managed by 6875...
Could you ensure that CPU is correctly running (Reset high, activity on adress bus, on data bus, etc...) ?
Could you ensure that CPU is correctly running (Reset high, activity on adress bus, on data bus, etc...) ?
Hi. OK so, Reset is not always low as stated before. Regular reset is not always a fault, this could be a feature generated by a watchdog, but if so signal is likely to be inverted (short reset time and long running time).
Check the 5V supply. We have a periodic pattern with 20ms repetition rate : 50Hz ! this could be main power related.
Do you have a scope? in order to check reset input pin of 6875 in an analog way (analyser is digital)
Circuit diagram are now required!, could you draw the circuit connected to reset input of 6875 ?. For such a simple board we expect a RC to ground, but with such a waveform this may be more complex! ie : a main frequency sync mechanism.
Check the 5V supply. We have a periodic pattern with 20ms repetition rate : 50Hz ! this could be main power related.
Do you have a scope? in order to check reset input pin of 6875 in an analog way (analyser is digital)
Circuit diagram are now required!, could you draw the circuit connected to reset input of 6875 ?. For such a simple board we expect a RC to ground, but with such a waveform this may be more complex! ie : a main frequency sync mechanism.
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