Finished
Now finally, if and who ever might be planning to do some work on his (or her???) SX828 and is interested in what I did, here it is:
The following list refers to the SX-828 Model FVZW Service Manual here on AK.
All electrolytic caps are Nichicon types if not otherwise noted; almost all parts can be found by mouser via entering parts type, and all Panasonic electrolytics could as well also be Nichicons.
Where I used certain stacked polyester film caps, f. e. ‘MKS’ type, one can as well use any other stacked film cap, f. e. Panasonics ECQ-type or CD (Cornel-Dubiliers) DSF-types.
At certain places I used much higher voltage rated electrolytics ONLY because more suitable values I had not at hand.
I did power supply and protection first and proved that receiver is functional at LEAST soon after any board was finished (otherwise it will KILL YOU if you’re up to search for an error if you did all at once).
Common parts, pg. 20:
original: -> new
designation: type µF/V -> type µF/V of replacement
C5 CEA 220/6 -> Panasonic RAD FC 220/25
C6, C7 ACH 8000/50 -> BCComponents 10000/63 series 050/052 (main filter caps: new ones have less diameter than original, adaptation necessary); each paralleled with an MKS-4 4.7/250 stacked poly film cap
C8 ACH 1000/63 -> UPW 1000/200
C9 CEB 470/16 -> TVX 470/25
D1 SIB01-01 -> 1N4004
Head amp unit W21-002, pg. 35:
C1, C2 CEA 22/10 -> UKL 22/50 + paralleled 1,0/50 stacked poly film cap (preferably Panasonic ECQV (or Cornell-Dubilier DSF))
C3, C4 CEA 4.7/16 -> UKL 4.7/50
C5, C6 CEA 10/25 -> UKL 10/50 + paralleled MKS-2 0.47/63
C15 CEA 220/25 -> UPW 220/50
AF-Unit AWK-012, pg. 37:
C11, C12 CEA 47/6 -> UKL 47/35
C13, C14 CEA 47/50 -> UPW 47/200 (is overkill, but was at hand)
C15, C16 CSSA 1.5/25 -> MKS-4 1.5/50
C25, C26 CSSA 3.3/25 -> UKL 2.2/50 + paralleled 1.0/50 stacked poly film cap
C27, C28 CEA 100/6 -> UPW 100/63 (overkill)
C29, C30 CEA 47/50 -> UPW 47/200
C31, C32 CSSA 2.2/25 -> a bunch of paralleled poly film caps 1.0, 0.68 and 0.56 µF, all rated 100V
C37, C38 CSSA 1.0/25 -> ECQ 1.0/50
C43, C44 CEA 100/25 -> Panasonic RAD FC 100/35
C45, C46 CSSA 3.3/25 -> UKL 2.2/50 + paralleled 1.0/50 stacked poly film cap
Q3, Q4 SA725 -> KSA992FBU
Q5…Q8 SC1312 -> KSC1845UBU (UBU no longer available)
Main amp unit (AWH-010)
C1, C2 CSSA 1/50 -> ECQ 1/50
C5, C6 CEA 22/6 -> UKL 22/50
C9, C10 CEA 220/10 -> UKL 220/50
C11, C12 CEA 100/50 -> UPW 100/63
VR1, VR2 0…4.7 kOhm -> 0…5 kOhm 25-turn var. pot 64Y-5.0K, these are for OFFSET
VR3, VR4 0…100 Ohm -> 0…100 Ohm 25-turn var. pot 64Y-500, these are for BIAS
I measured resistance of desoldered originals and set replacements to these values before soldered them in (kept track of pin orientation).
Q1, Q3 SA572 -> KSA992FBU (two that have a close matching hFe-value, f. e. 740 and 741)
Q2, Q4 SA572 -> KSA992FBU (two that have a close matching hFe-value, may differ slightly from Q1, Q3)
Q5…Q8 SC1121 -> KSC2690AYS
Q9, Q10 SC484 -> KSC2073TU + heatsink V 5801B (heat resistance 27 K/W) + non-conductive thermalcote (nonetheless sink may be electrically alive but does not touch anywhere, enough room in vicinity)
Q11, Q12 SA484 -> KSA940TU + heatsink V 5801B (heat resistance 27 K/W)
Q13, Q14 SC1080 -> MJ15024G OnSemi + TO-3 Mica + non-conductive thermalcote, there MUST NOT BE conductivity to the heatsink
Q15, Q16 SA680 -> MJ15025G OnSemi + TO-3 Mica + non-conductive thermalcote, there MUST NOT BE conductivity to the heatsink
Power Supply AWR-010
C5 CEA 1000/10 -> UPW 1000/35
C6…C9 CEA 100/50 -> UPW 100/63
C10 CEA 220/16 -> Panasonic RAD FC 220/35
C12 CEA 220/35 -> UPW 220/50
C13 CEA 470/16 -> UPW 470/25
R12 MOX 330 Ohm/ 2 W -> metal oxide film 330 Ohm / 2 W
Q1 SD234 -> KSC2073TU
Q2 SC373 -> KSC2383YBU
Q3 SD313 -> KSC2073TU
Q1 and Q3 get a selfmade heatsink (as can easily be noticed...)
D7 WZ130 -> 1N5243
Protection circuit AWM-025-C
(Attention: The manual shows W28-008, but in my SX828 the AWM-025-C can be found. This is the protection board of later production SX838, which is completely different but can be found in the SX838’s manual pg. 48)
C1, C2 CSSA 0.22/10 -> MKS-4 0.22/100
C3, C4 CEA 330/6 -> UPW 330/25
C5 CEA 4.7/25 -> UPW 4.7/50
C6 CEA 100/16 -> UPW 100/25
Q6 SC945 -> KSD1616AGBU
Q7 SC1384 -> KSC2690YSTU
I added the diode ‘D9’ 1N4004 between pin 9 and 10, banded end on pin 10 (to kill shut-off generated voltage hitback on Q7), as always has been recommended by you-know-who
After all work is done:
First run is on DBT for live-of-the-unit-insurance reasons.
Without DBT then bias and offset is addressed:
The bias measuring points for the left channel are pins # 11 (pos lead) and pin # 17 (neg lead).
The bias measuring points for the right channel are pins # 12 (pos lead) and pin # 18 (neg lead).
The BIAS target voltage might be 20 millivolts (0.020 V) as the average guess of some qualified other AK-members here.
Offset voltages can be measured for the left channel on pin 7 to ground and for the right channel on pin 8 to ground.
The OFFSET target voltage is zero volts (0.000 V) with NO SIGNAL.
This is what I did, not necessarily the only or best solution. Errors must be credited to me, almost anything else to EW and/or MTF.
The pics show the finished main amp, the new outputs with the STV4's on the heatsink, the AF-Unit before and after modification.
Frank