Maybe that's why you sometimes require "dozens" of donors to find one that is compatible?



In some cases or families DCM does matter. Unicorn / Sabre is one of them.

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you may think whatever you like, the fact is that I recover these with one donor (without bugging with cover and axle), even if the DCM completely mismatches. (of course if the surface is in good condition).

pepe

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Well, you certainly know something I don't!

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pepe,
Once I accumulated about 100 donors.

Nor any particular problems with the restoration Sable, Unicorn and kind.
without bugging with cover and axle.
If nature, of course if the surface is in good condition.

In the DCM is not looking.

We are talking about case where original heads are working in donor, but on client drive is possible to read only one surface (if drive has 2 heads)? Good heads (even original working heads) can't read other surface (clicking).
Right?
First time I thought same thing like pepe - it's bad pcb killed servos. But when I tried to use this pcb on good donor and I never get chance to get donor with killed servos like client drive. So I got data by trying a lot of donor heads on this client drive (like Tomset). And DCM is nothing for those cases. I had about 5-6 cases like this. On first 3 I didn't recover data on bad surface.

i don't just THINK it killed servo (and data), i precisely prove it (mainly for myself) in order to take the neccessary steps. If it is killed, there's not much to do on the area striked through.

Tomset, you said you had to use a bunch of donors to get satisfactory result. When i have a case requiring that many efforts, i call it a problem. Or rather a difficulty.

drHDD: i made a detailed description of the problem quite a few years ago. I also know which component is responsible for the phenomenon. Also met some drives that just started clicking sometimes, but did not kill the servo, and they were working fine for various intervals of time. All these can be possible due to the same failure on the pcb. It does not always end up the same level of destruction.
So i would be careful with the pcbs having the slightest suspect of being affected.

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I don't know what to say. Client pcb didn't kill donor drive, after about 2 weeks of use. I found good heads to read data (checked about 70 sets of heads). It happened 2 times already. Both times original heads were perfectly working in donor drive. One surface I was able to read by almost any heads, other one I read by only one set of heads and other sets of heads were clicking.
upd Both times head sliders which were start working with problem surface were kind of turned a little bit relative to normal slider position. Original head sliders were look kind of the same.

and did they read the whole surface without problems that the others could not read?
if so, it was not servo problem just a weak head and other 'incompatibility'.
It is very hard to tell what it was without measuring the actual case.

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No, they didn't read whole surface. Time to time drive was start clicking.
I agree - better to talk about those cases with actual drive in hands.

if it started to click from time to time, it had the servo damaged on the half of the user area, probably not very seriously, 'just a little bit'

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Dear Friend Pepe.

I know what is in ur mind and what you are talking about. you are correct no need that too much donors that tomset talking.

Yours Friend
Jignesh Pankhania

My mileage varies, as follows:

1) Except in cases of gross PCB failure, PCB has little to do with this problem, because trying multiple (good) replacement boards usually yields no improvement.

2) The original "problem" with these drives -- even on newly minted ones from the factory -- is that the track widths were narrow, and with temperature changes & etc. the drives could lose ability to read servo. Track widths in later models such as Royal were widened, and that is why lid position in later products is not a factor.

3) Cover alignment DOES matter. I'm working on a Mammoth 80 GB drive right now with replaced heads. In order to read head 1, I have to physically adjust the lid's position so that it changes the zenith of the hub. It 's a physical problem with a physical solution.

4) DCM is largely irrelevant. But my understanding -- which may be wrong -- is that the 5 & 6th characters of DCM in these families indicate preamp and head or slider types. I have found the info there to be pretty consistent.

5) Slider pattern matching does matter.

We have been recovering these drives for years. The above work for us.

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Dear Friend Juno
+4 For You.
not 5 full bcoz still something missing

Hi Jono,

excuse me, but most of the above is BS, track widths have nothing to do with the described symptoms. there are 2 main causes, one of them is a failing resistor in the feedback path of the -5V supply generator, the other one is the oxidation of the metal layer in the vias, which can occur in the same feedback path.

People adjust cover because they have no better method, and because they have perfectly no idea why 'aligning' the cover helps.
One can get info about preamp and head type from DCM but it is not always at position 5 and 6.
Slider pattern matching can be reduced to match the appropriate DCM figure, but it can be tricked as well, that's why i said it is not really important to me.
I prefer MHAs with a matching preamp and head type, but if i do not have it on stock, it is not the end of the world.

pepe

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Pepe:

You needn't take my word about the track width being a factor in some of the problems, but it is a fact from an unimpeachable source.

You can monitor the HDU signal with a scope while aligning the lid, and see of yourself what happens. And many of the heads are contaminated and require cleaning, which rules out any electronic PCB causes. I wonder why lid alignment variations "work" if the etiology of the problem is non-mechanical?

I know that no "rules" seem to be hard and fast . . . there are exceptions to almost all of them. That's what makes this business particularly interesting . . . to try to determine patterns of failures and come up with a reliable "solution" to them. I know you recover a lot of drives, too. It's fascinating to me that your solution to these problems is TOTALLY different from mine, yet both work?!

Cheers,

Jono

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Is micro jogs worth the other point?

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Does not require game any cover or resistors.
Suitable head immediately without any settings read surface.
Suffice it to select the options you want donor to immediately deliver the desired.
But it is very rare in a donor all heads coincide with the patient.
Necessary to use three or more donors depending on the number heads and coincidence.
One donor for hot-swap.

is it just me seeing some contradiction here ?

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pepe,
I can not in English to convey his thoughts.
Alas. Only through the Google translator.
I read - I understand, but I can not say right.
Like a dog.

ok, i understand
np

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