\section{Overhauling the tape drive mechanism}
The HP9830 tape driver suffers many fewer mechanical problems than the card 
reader or printer of the HP9810 and HP9820 machines,and that that do 
occur are generally easy to repair. It is necessary to remove the 
mounting bracket and front panel for almost all repairs, the head plate 
and drive spindles can then be dismantled as necessary.

\subsection{Initial dismantling}
Begin by removing the rear mounting bracket which is fixed by 4 screws. 
Unplug the 4 `plugs' (actually PCBs with pins soldered to them) from the 
{\bf Tape Drive Connector} PCB.

These plugs connect to the following parts of the drive : 
\begin{description}
\item[S -- Solenoid (9 pins)] : The 2 solenoids that rock the motor beam and 
the `write protect' and `cassette in' microswitches
\item[M --Motor (5 pins)] : The 2 drive motors
\item[P - Photo (5 pins)] : The optical EOT sensor
\item[H- Head (9 pins)] : The {\bf Tape Head} PCB
\end{description}

The {\bf Tape Drive Connector} PCB is held to the bracket by 3 screws,
loosen these a few turns at a time to separate the PCB from the bracket.
Normally the screws and spacers stay with the bracket, the threaded ends
of the spacers unscrew from the tapped bushes on the PCB. 

Next remove the tape drive front panel. It is retained by a long
through-bolt. With the tape drive front-upwards. remove the nut, washers
and spacer from the end of this and then pull out the bolt with a further
spacer and washers. You may want to store these parts on the bolt and
refit the nut by a few turns. Lift up the front panel and slide out the 
window. Remove the nut and bolt holding the earth wire to the front panel 
and remove the panel entirely.

The motors are removed next. Take out the screw on the motor beam pivot 
post and the 4 screws holding the rear bracket to the sides of the drive. 
Take off this bracket and slide the motor assembly off the pivot.

\subsection{Dismantling the head plate}
The tape head is connected to the {\bf Tape Head} PCB by 4 wired fitted 
with push-on contacts that go onto the pins of the head. Remove these, 
noting their positions  then remove the 2 screws and spacers holding 
the PCB to the head plate assembly. Put the PCB aside.

Remove the 3 screws holding the left-hand cassette guide to the head plate 
Ease off the guide and unhook the cassette holding leaf spring from 
inside the frame. Remove the 2 bushes form their pins on the chassis 
(these often fall off if you are not careful). Free the right hand guide 
from the similar bushes on the right side of the drive chassis and remove 
the complete head plate. Again remove the bushes before they fall off and 
get lost.

The optical EOT sensor PCB is retained by 2 further screws. Remove the 
guide from the front of the sensor and remove the PCB complete with the 
LDR and light bulb. This bulb is one of the common failures of the tape 
drive, it is a 5V 60mA T1 wire-ended bulb\footnote{For example Farnell 
113-9296} You can easily check this for continuity and solder in a 
replacement at this stage.

It is not advisable to remove the head, it would have to be realigned 
when it is refitted. I have never done this, but maybe one day\ldots

\subsection{Dismantling the drive spindles}
On the main tape drive chassis, remove the motor beam pivot post which is 
retained by 1 screws.

It is possible to remove the drive spindles without removing their leaf 
springs first, but it is a little tricky. It is a simpler to remove the 
single screw from the rear face of the drive wheel and lift off the leaf 
spring. Then remove the circlip and plastic washer from the front end of 
the spindle. slide the spindle out rearwards, and recover the second 
plastic washer.

The 'tyre' on the drive wheel is the other main failure point of this 
drive. It is a size BS219 O-ring\footnote{This O-ring is 1+9/16'' outside 
diameter, 1+5/16'' inside diameter and 1/8'' thick} and can easily be 
replaced at this point by stretching it over the drive wheel.

The brake plate is retained by 2 screws. Remove these, free the return 
spring and remove the plate and its spacers. The latter are asymmetrical 
and must be refitted the correct way up.

\subsection{Initial electrical tests}
Clean all the parts of the tape drive, paying particular attention to the 
head face. 

Some of the electrical parts of the tape drive should be tested at this 
point. The resistance of each drive solenoid (measured between the pins 
on the connector `plug' PCB should be around 22$\Omega$. The drive motors, 
again checked at the pins on the `plug' should be around 10$\Omega$. Also 
check the filament lamp in the EOT sensor if you have not already done 
so. The head windings can be checked for continuity, but as in the case 
of the card reader use a low-current tester and demagnetise the head 
afterwards.

Then reassemble the tape drive and fit it, and the 4 PCBs in the tape 
control section, to the machine.

\section{Repairing the tape drive electronics}
Although the tape drive controller is much more complicated than, say, 
the card reader system of the HP9810 or HP9820, it is quite 
straightforward to repair. One reason is that HP intended it to be 
repaired to component level in the field, and provided some very useful 
testpoints on the PCBs. The HP service manual for the HP9830 includes 
some information on troubleshooting this section, but it suggests you 
find the faulty board by boardswapping, which is something that I will 
never recommend.

Begin by pressing the rewind key on the keyboard. This will set U4a on 
the {\bf Tape Controller} PCB (even if the reset input of this flip-flop 
is low, the Q output will be high while the rewind key is pressed). This 
will cause all 3 control signals to the {\bf Motor Control} PCB to go 
low, The appropriate solenoid and motor should operate turning the 
supply side spindle. If not, then check that TP5, TP7 and TP8 on the {\bf 
Tape Controller} PCB are all low. If not, troubleshoot the the motor 
control logic on the {\bf Tape Controller} PCB. If these signal are all 
low, check the direction control logic on the {\bf Motor Control} PCB to 
fund out why the solenoid isn't engaging or the speed control circuit on 
the same PCB id the solenoid operates but the motor doesn't.

Now take a scratch tape, and using an audio cassette recorder, 
fast-forward it off the clear leader. Put this in the HP9830 drive and 
press the rewind key again. The rewind flip-flop should now latch on, 
the tape should rewind to the leader and stop. Problems here can be 
caused by the rewind flip-flop, U4 on the {\bf Tape Controller} PCB, the 
end-of-tape logic on the {\bf Tape Interface} PCB, or the EOT sensor 
itself. It is also worth checking that {\bf CassSw} is high, If the 
microswitch in the tape drive is not properly detecting the cassette, 
U4a's reset input will be kept low.

Next initialise the tape in the usual way. The forward drive should now
engage (on the {\bf Tape Controller} PCB, TP5 should be low and TP7 and
TP8 high). If these signals are incorrect, check if {\bf TapeSel} (on TP2
on the {\bf Tape Controller} PCB) is pulsing high. If not, check the
selection logic on the {\bf Tape Interface} PCB and if necessary the {\bf
CEO} signal logic on the {\bf I/O Interface} PCB. If {\bf TapeSel} is
pulsing high, check U10, U8 an the {\bf Tape Controller} PCB. 

If the motor control signals are correct but the tape motion isn't, again
investigate the {\bf Motor Control} PCB as described above. 

While the tape is initialising, the write signals should all be active. 
Check {\bf WrClk} on TP10 of the {\bf Tape Controller} PCB, write data on 
TP9 and {\bf WrMark} on TP10. If they are all missing, check that the 
write clock oscillator is running (TP1 is the output of this circuit). 
Also check that the bit counter and the data shift register are working 
correctly. Moving to the {\bf Read/Write} PCB, the BMS-encoded data can 
be checked on TP2 and TP3. Unfortunately the 5V supply to the write 
buffer on the {\bf Tape Head} PCB is not available on a test point but it 
may be worth checking that this is present if you have problems with writing.

If you get an error suggesting that the tape is write-protected, the first
thing to check is the write protect microswitch on the tape drive itself.
Mechanical switches cause a lot more problems than electronics! 

If you have a printer, next try listing the tape. This will check the read 
function. During this you should see transitions on TP6 and TP7 of the 
{\bf Read/Write} PCB (if either is missing, check the read amplifiers and 
the head itself) and then check there is {\bf RdClk} on TP10, {\bf 
RdData} on TP4 and {\bf RdMark} on TP9. If these are correct but the 
listing operation fails, check the data shift register and associated 
control logic on the {\bf Tape Controller} PCB and the flag logic on the 
{\bf Tape Interface} PCB.

If you don't have a printer, try saving a short program to the tape. At 
the start of the save operation, the system reads the file headers from 
the tape and thus the read signals can be checked during this time. Then 
try loading the program back in, if this works, the tape system can be 
considered to be operational, if not, the fault is probably on the {\bf 
Tape Controller} PCB around the data shift register or the {\bf Tape 
Interface} PCB around the data flag logic.

\section{Beeper}
The beeper is simple to troubleshoot. Perform some operation that causes 
an error, and which therefore should cause the beeper to sound. If it 
does not, check the {\bf CROut} signal from the {\bf I/O Interface} PCB 
is being asserted, if not, check the source of this signal. If it is, 
check U12 on the {\bf Tape Interface PCB} is changing state. 

Then check that the oscillator U15a and U15b is running, and that during 
the beep a square wave appears on the output of U15d. Finally check the 
loudspeaker driver transistors and their associated components.

