Still waiting for parts so am going thru the board capacitor by capacitor and I see few discrepancies. What is the correct value of C4? 4700 or 2200uf? What is the correct value of C52? 47 or 4.7uf? What is the correct value of C53? 47 or 4.7uf? There is a C701 and C16 marked on the board but I do not see it listed in the parts list. There is a C901 and C13 on the parts list but not on the board.
Harman Kardon CD491
- Thread starter vegas79
- Start date
genesmasher
Active Member
Make sure you are using the right service manual revision. It is called "supplement 1" on hifiengine.
C4 is 4700uF - value change in this revision. Only original revision is 2200.
C52 and C53 are next to each other - go by what's installed on the board, or check schematic corresponding to your revision. configuration change in this revision. I think they mislabeled the board here.
ignore caps that are not currently installed. C901 (0.47/50V) and C13 are an inch below C11, if installed.
C4 is 4700uF - value change in this revision. Only original revision is 2200.
C52 and C53 are next to each other - go by what's installed on the board, or check schematic corresponding to your revision. configuration change in this revision. I think they mislabeled the board here.
ignore caps that are not currently installed. C901 (0.47/50V) and C13 are an inch below C11, if installed.
The location C16 noted above could be C18 (hard to read) but either way their is no parts listing for C18 or C16 under PCB-2. Could this be C13 mismarked as I don't see a C13 location on the board even though the parts list says there is on with a 470uf capacitor? Could C701 marked n the board be mismarked and should be C901. There is currently a 47uf in C53 and a 4.7uf in C52. Should these not be switched based on parts list.
Parts did arrive. I have replaced the faulty IC1 and shorted R20 & R27 resistors. Also replaced the Fine Gold Caps for Nichicon 105 degree caps. I definitely have continuity between IC1 pin 2 and Q5 collector. I will reinstall the PS board tomorrow and see what we have. I have not had a chance to order a Q5 transistor so it may or may not be ok.
C16 (as well as C17) are located near the transformer secondary leads as shown below.
Been listening for a half hour or so and this deck sounds very dull and muffled. My two cheapy 3 head decks are 10x better. Wonder if there is something else wrong. Powers up (Comes out of wait mode within 5-7 seconds, all control buttons work but their is NO detail in the sound at all. Any thoughts?
Everything works as it should and have tried 10-15 tapes on it. The same tapes that sound bad on the 491 sounded great on the Yamaha and Technics deck.
I also noticed that along with the poor sound there is not much volume. Tried it with two very good amps and the same muffled sound and low low volume. The heat sink that the large transistors are attached to is very very hot. Not sure if the problem is still related to the power supply or another issue.
While playing a tape, see if you can visually check to make sure that the tape is riding perfectly flat on the playback tape head and not touching the tape guide. The problem could be that there is still an electrical issue or it might be a mechanical issue.
OK I will have a look. Not sure if you saw my remark that the heatsink for the voltage regulator and larger transistors is very warm almost hot.
Which transistors are you referring to? #1 or #2 on photo? Can you see which of the transistors is hot... careful!!?
Number 2 area. That heatsink is very warm but hard to tell which one(s) are the hottest. The voltage regulator IC1 seems to be be one of the hottest. Should it be that hot? Hard to tell if the tape is riding in the guide but I tried wiggling the tape and pushing lightly on all four corners. When I push the upper right section of the tape the music improves considerably. It comes to life If I push and hold it.