Harmon Kardon CD491Low distorted Rt chan Record Audio, No PB Audio, HA12058 IC issue - UK Vintage Radio Repair and Restoration Discussion Forum

sirejohn · 27th Oct 2011, 7:06 pm

In Rec/Line monitor mode, Rt Chan HA12058-01 IC502 has approx 90 % of all DC voltages way off. Signal input OK, output loses exactly lower half of sine wave. Swapped same L & R ICs 501 & 502 - no help. Svc Manual has no desription of Dolby IC internal process. Comparing resisance checks from each IC 502 pins to ground is same as functional IC 501 Lt Chan - no help.
Does anyone have a datasheet of Hitachi HA12058-01 Dolby B/C IC? Or other ideas?? TIA

Mooly · 27th Oct 2011, 7:38 pm

I would guess something like a small passive that has gone leaky... ceramic cap etc. Maybe if you posted a pic of that section of the circuit.

sirejohn · 4th Nov 2011, 12:16 am

Made comparison measurements between Working L-Chan PB IC 501 & No R-Chan PB output on pin 24 & 25. Pin 4 input OK and pin 24 & 25 flatline zero amplitude. Pin 24 norm volts= 4.2. Defective IC502 pin 24 & 25 = 1.2 VDC.
Disconnect output coupling cap C528 = no change. Ordered repl IC502 - outcome TBD

Mooly · 4th Nov 2011, 8:20 am

Didn't you swap L and R HA12058's over ?

Would have to see the circuit really...

27th Oct 2011, 7:06 pm	#1
sirejohn Retired Dormant Member Join Date: Sep 2011 Location: Sherman Oaks, CA USA Posts: 12	Harmon Kardon CD491Low distorted Rt chan Record Audio, No PB Audio, HA12058 IC issue In Rec/Line monitor mode, Rt Chan HA12058-01 IC502 has approx 90 % of all DC voltages way off. Signal input OK, output loses exactly lower half of sine wave. Swapped same L & R ICs 501 & 502 - no help. Svc Manual has no desription of Dolby IC internal process. Comparing resisance checks from each IC 502 pins to ground is same as functional IC 501 Lt Chan - no help. Does anyone have a datasheet of Hitachi HA12058-01 Dolby B/C IC? Or other ideas?? TIA

27th Oct 2011, 7:38 pm	#2
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Harmon Kardon CD491Low distorted Rt chan Record Audio, No PB Audio, HA12058 IC is I would guess something like a small passive that has gone leaky... ceramic cap etc. Maybe if you posted a pic of that section of the circuit.

4th Nov 2011, 12:16 am	#3
sirejohn Retired Dormant Member Join Date: Sep 2011 Location: Sherman Oaks, CA USA Posts: 12	Re: Harmon Kardon CD491Low distorted Rt chan Record Audio, No PB Audio, HA12058 IC is Made comparison measurements between Working L-Chan PB IC 501 & No R-Chan PB output on pin 24 & 25. Pin 4 input OK and pin 24 & 25 flatline zero amplitude. Pin 24 norm volts= 4.2. Defective IC502 pin 24 & 25 = 1.2 VDC. Disconnect output coupling cap C528 = no change. Ordered repl IC502 - outcome TBD

4th Nov 2011, 8:20 am	#4
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Harmon Kardon CD491Low distorted Rt chan Record Audio, No PB Audio, HA12058 IC is Didn't you swap L and R HA12058's over ? Would have to see the circuit really...