After investigating further, I found that: 1. there are cassettes on which FWD vs REV play ok in terms of high frequencies 2. there are cassettes on which FWD (always) gives way more HF than on REV mode (both cassette side A and side B) 3. there are cassettes on which REV (always) gives way more HF than on FWD mode (both cassette side A and side B) Why? WHY?????? The HF loss is consistent.
HF loss and imbalance are both caused by that tape curling which essentially messes up the azimuth. Head sitting at an angle (when engaged) or uneven head wear can also create similar symptoms. In such situations some tapes may work fine, giving the false impression tape path alignment is fine. What you mention at points 2 and 3 suggests you have problems on both FWD and REV and they manifest depending on the tape used. If there's really no visible misalignment of the pinch rollers and capstans (but you really want to thoroughly check that's not the case), I would start to do the following items: - lubricate both capstans bearings with watch oil (note you will need to clean the capstans after that); - roughen both capstans with ferric chloride just to make sure their surface is rough and has no non-uniformities that tend to pull the tape up or down; - replace the pinch roller rubber tires, even though they look mint they might still have a problem;
1. Yes, at this point there is absolutely no visible misalignent of the capstans. However regarding the pinch rollers it is hard to say, as the entire head-set plus pinch rollers (everything which is inside the door compartment) seems at an angle even when PLAY engaged. Although there doesn't seem to be any kind of "bent" part... 2. I've already lubricated everything 3. Regarding the DD9 rubber kit - ok, I'll bear that in mind. Could you please elaborate on roughening the capstans? Maybe a step-by-step on how to do that? How liquid should be FeCl3? How concentrated? Do I apply it with a cotton swab while capstan is rotating?
Head sits on a foil spring, so note it's normal to sit at an angle in stop, especially when door is not closed or remvoed. However if it sits at an angle when engaged, the lever pushing it is bent or something is restricting the movement. To be noted foil spring has some adjustment in it and it's best to adjust it to the loose position for easy engagement and to avoid stressing the camgears. Rollers sitting at an angle indicate either a carriage problem or both roller bracket holding pins are either bent or have play (they need to be glued in this case). As for the FeCl3, the one I use is 40% concentration and it's the dark brown liquid type. Think it's the most common type available on the market but don't quote me on that. You use a cotton swab, immerse it in the substance and rub it against the capstan while it is rotating. Do that just on the area where the tape rides. You will need to put the unit in REW (so pinch roller doesn't sit on the capstan) and rub the swab against the capstan for a couple of seconds (in FF unit will stop automatically after a few seconds) until it becomes matte. After this you need to clean the capstan with IPA and then put unit in play and clean both capstan an pinch rollers just to be sure there's no trace of substance left before inserting a cassette.
Tonight I will provide some photos with head/rollers/everything in both open/closed and engaged state.
Here, I've made a small photoset for my DD9. Please pardon me the dust, it isn't the point I believe https://drive.google.com/drive/folders/1JXTbSTf0YjEvUUublVZ6OIkw-0aDGKCn?usp=sharing
Here, check this: Seems that when engaging, the head set is not lifted up evenly: back part (closer to the case) is lifted higher than the front part. What can be the reason for this? I tried with my nail and there is nothing which would block the head from lifting further. I checked thoroughly and can't see any option here...
Even though there is nothing to report, I will report anyways: I've disassembled the head carriage and found 2 tiny thin rectangular plastic sheets behind the head (between the head and the carriage itself). They look like something off factory, however there is no such thing in the service manual. When I removed them, finally the head and tape guides were inline. However the entire head carriage was still at a serious angle (as seen in the video). After thorough inspection, I wasn't able to find anything suspicious. Also I wasn't able to reason what could possibly lead to head being lifted unevenly (in theory eveyrthing should have been working fine...). So I did some bending job. As a result - the head carriage is now completely inline with pinch rollers/capstans and perpendicular to their axis. However not a single thing that I've done made any change to the HF loss effect. At this moment, if I gently lift the front (outward facing) part of the head just a tiny bit, the HF are back. However if I do that gentle lifting, the opposite playing direction starts losing HF a bit... Also I wasn't able to make up any option on how to preserve that gentle lift. Right now all of this makes little sense to me. Maybe my 1989 copy is somehow faulty... Maybe it lacks something... Sad
I just like to see tech questions posted in this area and not introductions. A lot more people read through here then up above and you'll get a better response to your questions. It also helps when searching for solutions to issues other users might be having. Good luck with your repair!
Reading this thread I summise that you're just shooting blind into a haystack without really effectively diagnosing what the issue could be. No offence to Valentin for his helpful suggestions but I would respectfully suggest either investing in the correct tools that could help you pinpoint and diagnose the issue; service manual (first and foremost, if there is one) ... calibration tapes, mirror tape, M300 gauge, oscilloscope, etc. or send it to someone who knows what they're doing. Deb64 has refurbed my D6C. I'm not sure if she is au fait with the DD9 but you could always ask!
@Chris_D Thank you for your reply! Actually I do have several calibration tapes, four oscilloscopes, DD9 service manual and some experience in addition to that So I am not doing this naked! But thanks for your input anyways! P.s. I wasn't able to find a mirror tape for sale, when I started with this issue
The M300 gauge in combination with an FR calibration cassette and oscilloscope could help you rectify the frequency imbalance issue. Someone on TH was selling home-made mirror tapes here They're also all over ebay here
