Question arround the Power Supply of Linn's Preamp LK-1
I don't understand, how works exactly the section arround U9 (LM324).
The only thing, that's clear for me is the fact, that the neg. voltage exceeds exact the same value as the pos. voltage.
But what about the zener D4 so as the upgrade Zener diode between PIN 5 from RA11 and PIN13, U9?
Also very interesting for me is the purpose of Q95 so as the connection from its emitter to the "NMI" PIN 4 from Hitachi's MCU HD6303 - please note the missprint in my own schema at this PIN - please refer the genuine schema, last two pages about
In the datasheet from HD6303 I read follow:
When the falling edge of the input signal of this pin 4 is recognized, NMI seqence starts. The current instruction is continued to complete, even if NMI signal is detected.
Interrupt mask bit in Condition Code Register has no effect on NMI detection.
In response to NMI interrupt, the Information of Program Counter, Index Register, Accumulators and Condition Code Register are stored on the stack. On completion of this sequence, vectoring address $FFFC and $FFFD are generated to load the contents to the program counter.
Then the CPU branch to a none maskable interrupt service routine.
But I don't understand the consequence concerning LK-1 operating, when PIN 4 (NMI) isn't connect to the Emitter of Q95.
In cases, where I provide for the control board (front-PCB) an independend power supply include independend transformer I must cut this connection, otherwise there are no commands accepted after pressing the bottons.
Thank you for advices.
various LK-1 devices are very sensitive against personal computers in the vicinity (frozen display after switch on the personal computer, no command acceptance possible).
Other LK-1 devices are not sensitive against that.
I assume, the cause is related to the NMI PIN of the HD6303
nobody here who is familiar with the LK-1 MCU section?
I am still hoping for informations.
ANGIELSKI HI END LINN LK1 LK280 ko?cówka +preamp (922265572) - Archiwum Allegro
I read follow (probably quotation from Service Manual) :
EPROM software uprated, power supply improved;
anti glitch "piggy-back" modification fitted.
(Upgrade year 1987)
The mentioned piggyback was soldered by several LK1 devices on top of the dual inline case from U9 (LM324). C54 was not used in case of used piggyback.
At genuine schematic is hard to find, what elements are new and which modifications are additional performed.
On my own schematic drawing this is a bit more easy (look to part without number for new parts - Zener 7V5, 2x1N4148, 220R in place of the previous present short wire, cutting a PCB conductor to PIN 2+3 from RA11 and C55 and 6,8uF Tantal to PIN14 from U9 - go to attachments).
Is it important to note, that an introducing of this change also requires the here mentioned software update ??
That is an important question for me.
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