LF: Epson HX-20 service info

Dave Dunfield dave04a at dunfield.com
Sun Jul 3 18:26:32 CDT 2005


Fred, Sellam : Thanks for the info on "Uncle Roger", I'll keep it on file
as a reference.

Tony sez:

>             1000pF                                               VL
>    820k      C31                                                 ---
>     R78       ||                                                  |
> +--\/\/\---+--||----+         |\                 +----------------+
> |          |  ||    |      +--| >o-----+         |                | 
> |          /        |      |  |/ 2C/c  |         |           C12 ===
> |          \ R74    |      |           |         |          47uF ---
> |          / 390k   |      |  |\       |         V  D6            |
> |          \        |      +-=| >o-----+        --- 1S2075       --- 
> |          |        |      |  |/ 2C/b  |   10u   |               ///
> |  |\      | |\     |      |           |   C2    |
> +--| >o----+-| >o---+------+  |\       |  | []   |         +---VLD     
>    |/        |/            +--| >o-----+--| []---+--->|----+--------+
>  2C/d        2C/e          |  |/ 2C/a  |  | []       D7    |        |
>                            |           |           1S2075  |        |
>                            |  |\       |                   |        |
>                            +--| >o-----+               C1 ===   C6 ===
>                               |/ 2C/f  |             10uF --- 10uF ---
>                                        |                   |        |
>                                  D5   ---                 ---      ---
>                              1S2705    ^                  ///      ///  
>                                        |
>                                       ---
>                                       ///
>
>That's an ASCII-art version of the appropriate bit of the schematic. Section
>d )Input on 10, output on 10) and e (input on 11, output on 12) of IC 2C form
>the oscillator, the other 4 inverters are paralleled up as the driver.
>
>Hope that helps.

Thanks - it did. I followed the "AC" through, and could see a nice waveform
coming out of the 2C driver, however from there it degraded to what I described
before at the C1 cap - on a hunch I replaced C1, and the voltage rose to about
7v, and the display was readable, however it was also flickering, and I could
see the voltage rising and falling by a couple of volts - I replaced C6 and
now it's rock solid, and the display is perfect.

C1 and C6 were identical 10uf 16v caps, and that fact that both appeared to
have failed gives me concern for the other electrolitics in the machine, which
I will check out shortly... but notwithstanding that the machine is functioning
perfectly.

Next problem is that the microcassette drive appears to be "stuck" with the heads
and capstan forward - not really stuck, as you can push them back on their spring,
however they are not retained back as they should be - prevents inserting and
removing tapes - I haven't opened it yet, but will shortly ... is there any useful
info about the drive machanics in the service manual? I assume there must be some
kind of solinoid and latch to hold them back and release them?

Once again: THANKS! for taking the time to "ascii art" the LCD power supply
schematic ... VERY much appreciated!

Regards,
Dave
-- 
dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:
                http://www.parse.com/~ddunfield/museum/index.html





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