Read Gain Adjustment .1 General Information

7.9.2

7.9.3

7.9.4

The purpose of the read gain adjustment is to match the read electronics to the read head characteristics. The read amplitudes usually decrease with time as the head wears due to normal usage. Performing the read gain adjustment may then bring the amplitudes back within specification.

Drives containing Read Channel PCBAs revision E and earlier have two read gain ad-justment pots: One for 1600 cpi (PE) and one for 6250 cpi (GCR). Because the PE gain adjustment affects the GCR gains, always adjust the PE gains on these drives first.

The GCR gain adjustment does not affect the PE gains. The 3200 cpi (DPE) gains (on model 1260T are based upon the PE adjustments and do not require adjustment.

Drives containing Read Channel PCBAs revision F and later feature an automatic GCR read gain adjustment and have a read gain adjustment pot only for 1600 cpi.

All read gain adjustments are made while writing on a master output tape, and only after the write current adjustment has been performed. If a master output tape is not available, a new tape of the same brand and type most used at the site in question should be used.

The nine read channels are identified on the Read/Formatter PCBA. Each Read Chan-nel PCBA has its own testpoints on P3 at the outer edge of the PCBA. The analog ground testpoint AGND is located above P3.

When Required

After replacing the head or a Read Channel PCBA.

Equipment Required Oscilloscope, master output tape.

Procedure for 1600 Cpi (PE)

1. IMPORTANT: Verify nothing is connected to Jl and J2 interface connectors.

2. Turn power off, thread the master output tape, and set Sl and S2 on.

3. Turn power on and press LOAD to tension the tape.

4. After the BOT marker has past the sensor, press FPT to stop the tape.

5. Connect scope channell to pin 3 of P3 (read signal) on the fifth Read Chan-nel PCBA from the right and scope chanChan-nel 2 to testpoint ENVSUM on the Read/Formatter PCBA.

6. Select 1600 cpi by pressing FPT until the 6250 indicator goes out.

Qualstar Corporation

1260 Technical Service Manual

7-12

TP3 on Read channel PCBAS

v

ENVSUM on Read!

Formatter PCBA.

Figure 7-5 Read and ENVSUM Waveforms

V=3.0v DeEIK-t()-DI~aK

8. Sync the scope positive on scope channel 2 and adjust the timebase to obtain a signal similar to that shown in Figure 7-5.

9. Adjust R3 (R5 on revisions D and E) on the selected Read Channel PCBA un-til the preamble is 3.0 volts peak-to-peak at pin 3 as shown in Figure 7-5.

10. Head Alignment - If the head was moved or replaced for some reason, the tape wrap angle across the head must be adjusted. If the head position was not disturbed, skip to the next step.

Head Alignment Tool

95 degrees

Figure 7-6 Head Alignment Angle

500244 H

7.9.5

Chapter 7: Adjustment Procedures Rflrtrl \'rtin Arlill,tmpnt - - - ---- ----- -

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--_.-a. With the tape stopped, press FPT to select 6250 cpi. The 6250 LED must be on.

b. Press ON LINE to write forward.

c. Barely loosen the head mounting screws and see if there is any change in the amplitude of the preamble while rotating the head. It may help to in-crease the vertical gain of the oscilloscope and observe only the positive peaks of the waveform to see the difference in amplitude.

d. If the preamble amplitude changes while rotating the head, rotate the head to a position of maximum preamble amplitude and retighten the mounting screws.

e. If the preamble amplitude does not change, stop the tape by pressing FPT and use the head alignment tool to position the head to 95 degrees as shown in Figure 7-6. Retighten the mounting screws.

f. Press FPT to select 1600 cpi. The 6250 LED must be off.

g. Press ON LINE to resume writing and readjust R3 (R5 on revisions D and E) on the Read Channel PCBA until the preamble is 3.0 volts peak-to-peak.

11. Move scope channell probe to pin 3 ofP3 of the first Read Channel PCBA and adjust R3 on that PCBA for a peak-to-peak amplitude of 3.0 volts at the preamble.

Note: There should be no more than 0.25 volt of amplitude modulation on the read envelopes. Excessive modulation can be caused by a worn tape, a dirty or defective head, poor tape tracking, or excessive tape guide runout.

12. In like manner, adjust the remaining seven circuits.

13. Stop the tape by pressing FPT.

6250 Read Gain Check Procedure (GCR)

If the Read Channel PCBAs are revision F2 or higher, check the read amplifiers at 6250 cpi as follows (there is no adjustment):

1. Select 6250 by pressing FPT (6250 indicator on).

2. Press ON LINE and monitor each of the read gain testpoints. The amplitudes should all be about the same. Small differences among them are allowed. Do not readjust the gain pots.

3. Press FPT to stop the tape, and set Sl and S2 off.

Qualstar Corporation

1260 Technical Service Manual

7.9.6

This adjustment procedure applies to Read Channel PCBAs revision E5 and lower ONLY. These PCBAs can be easily identified by their two gain adjust pots. Revision F2 and later PCBAs feature automatic gain control in the GCR mode, eliminating the GCR read gain adjustment and its pot.

The adjustment procedure is identical to the 1600 gain adjustment, except that 6250 must be selected, and the adjustment pot is Rll on each Read Channel PCBA. Note that the 6250 indicator must be on. After adjusting the 6250 cpi gains, it is not necessary to recheck the 1600 cpi gains.