Decca | D25N 440 | Service adjust proc | PSU Use pot PP1 to adj HT for 151V ± 0.5V for 16:9 tubes at TSP28 terms.
Activating service mode
1. Switch on the appliance whilst holding MENU on set until red LED lights.
2. Release MENU button & press standby on R/C. Defaults to prog l - (make sure test sig is on this chan)
Functsto be selected using P+ & P- keys on R/C.
Control & adjusts = Vol keys.note initial values before adj. In the event of replacing NVM memory or micro, it is nec to make all adjusts accessible in service mode, since replacement memory is supplied without any prior prog & new micro reqs initialization.
1. IF video setting (IFxx AFCxx) adjust reqs special equipment & needed only for ICC2 N1 version,
recognisable by presence of LC7 coil. If the coil is present, adj IF & AFC to values given on label left side of main PCB so that a suitable approx is achieved.
If the coil is not present, adjust as follows:
IF 50, AFC 3
2. Initialization (INIT CTV 831 x (VERSION)
The init proc, which also indicates software version for micro, is enabled with Vol+ key & must be carried out whenever NVM memory or micro replaced.
Initialization has effect of erasing all data from memory except bytes option.
3. Screen grid voltage (Vg2 Test)
Select funct, press Vol+ key. A luminous hor line appears in middle of screen. Adjt pot G2 so that line is just visible (in a dimly lit room). Press Vol- & wait for few secs until service mode is restored.
4. Control bytes (Cox)
These are control registers that must be set as follows:
Co4 00, Co3 27, Co2 96
5. Option bytes (Opx)
Correct values to set for each appliance are given on label on back cover alongside notations Op3,0p2 & Opl.
6. Audio/stereo A2 decoder (LA/SA)
The LA & SA functs allow adjustment of separation between right & left audio chans, & of file respective levels. A RF stereo generator is therefore reqd.
Dis modulation to LH chan & adj LA for 1.4Vp-p at pin 1 of SCART 1 connector.Adj SA for min residual signal at pin 3 of SCART 1. If a stereo generator is not
available/set LA to 01 and SA to OB to obtain a
fair approximation.
7. Setting the luminance/chrominance delay (Yx)
The delay must be adjusted to the following values:
Yp 18 (PAL) (UK VERSIONS)
Ys 30 (SECAM)
Yn 20 (NTSC)
Yo 22 (SCART)
The Yn function is only accessible if signal is NTSC coded (standard accepted only by SCART)
8. On screen display (OSD)
Load fixed value 3F. (AUDIO MENU APPEARS)
9. White control (WB/WG/WR)
Using black & white bar signal, adjust to obtain a correct grey scale.
10. Hor geometry (TC/CP/PW/EW/HSH)
2 groups of these functions, 1 for 4:3 format (suffix 4) & 1 for 16:9 format (suffix 16), both of which must be adjust because they are used in zoom functs (4:3
tubes included). The functs of single parameters -
TC Trapezium correction (4 adjusts appear in 4 X 3 & 16 X 9)
CP Corner parabola correction
PW Parabola correction
EW Horizontal amplitude
HSH Horizontal shift
For 4:3 format tubes, enter EW16 = 3F to ensure proper zooming.
11. Vertical geometry (SC/VSH/VA/VS)
Vertical geometry adj starting with VS (vertical slope), which is set so that central horiz line of test signal is exactly at boundary between the visible image & black part below & must not be changed again. Functions of single parameters -
SC Vertical S-coirection (linearity)
VSH Vertical shift
VA Vertical amplitude
VS Vertical slope
12. AGC tuner setting (AG)
With a signal of ImV applied to ae i/p on UHF chan, adjust to 4Vdc at pin 1 of tuner.
13. De-activating service mode
Once all nec adjusts have been made, press TV or MENU OFF on R/C to memorise and return to normal operating mode | 14-09-04 |