My Rotel amplifier RA920AX has two mal-functioning switches - 1. MONITOR (Tape or source) 2. FUNCTION (phono, CD, , tuner, aux). The left channel crackles when you turn switches, so suspect wear on contacts inside switches. Do you know where I can buy replacement switches, please?

Replace the unit or have it repaired, you have no other options.

A turntable with a built-in preamp should not be connected to the phono input, because the preamp of the receiver or ampifier will be overdriven. The task of a preamp is to amplify the very low level of magnetic cartriges to the high level needed to work a line input and does some equalizing work to the signal. You can check if your turntable has a switch to disable the built in preamp (mostly they are low-end quality), otherwise connect the turntable to a high level input like "Tape", "AUX", "TUNER", "MONITOR", or "CD".

I assume you want to record from tape to computer and monitor the recordings later.
Simple three steps.
1) Connect the tape deck line out ( or labeled PLAY ) to any one of the inputs like Aux / Tuner using an 2RCA connector.
2) Connect Rec out from the SUV' to line input of your PC ( blue socket ) sound card.
3) To monitor your PC sound after recording on to Hard Disc , connect a cable between the PC sound out ( green socket ) and the the SUV Tape monitor IN ( sometimes labeled PLAY ) Now comes the tricky part.When you want to record on to your PC put the source switch on the SUV to where you have connected the Tape deck ( Aux / Tuner ). On the SUV keep the Tape Monitor switch to source ( released position ). After having done the recording to monitor and hear the Hard Disk playback turn on the Tape Monitor switch ( dipress it ). The pressing of the Tape switch on the SUV lets you toggle between the source and recording - In your case Tape deck and PC

PHONO is ONLY for TURNTABLES. That's why they don't call it AUX.

Wired as I described in the other request, the EQ will have effect of anything that amplifier uses for input once you engage the tape loop the EQ is installed on.

If the same channel is dead on the EQ as is dead on the amp there may be a correlation.

Let's break this into its two parts.

1) SU-Z550: You don't say WHAT source(s) you tried to use on the CD/AUX, TUner and PHONO inputs. The external device itself could be the source of the low volume. Try swapping the Left and Right cables to see if it follows the source channel or stays with the amplifier channel.

Check the controls on the amp to make sure you understand each one's effect on the sound.

"PHONO" is literal and exclusively FOR A TURNTABLE - NOTHING ELSE - EVER.

2) SH-8055: Equalizers don't 'boost' sound, they modify its levels at various frequencies. To do that they should be connected into a Tape loop on your amp. OUTs go to IN's. Then you select the Tape Loop on the amp and that inserts the EQ into the signal path of whatever source you're listening to. It's actions are BEFORE any other amplifier controls such as volume, tone and balance. The EQ itself also has a Tape Loop to replace the one it occupies. Make sure it is not enabled unless you have a Tape Deck on it to use. Choose "SOURCE". The blue LED display is to show you frequencies are present in the program material.

Set all of its lighted band controls at midpoint prior to declaring it defective. EQ is like any spice - a little is good, a lot ruins the recipe.

According to this listing I found on eBay it will work for you.

PYRAMID Stereo Control Pre-Amplifiers
PR2500

* Power On/Off Switch w/LED Indicator * Microphone Input Jack * Microphone Level Control * Bass/Midrange/Treble/Loudness/Balance Control * Master Volume Control * High/Low Frequency Filter * Stereo/Mono Switch * Muting Switch * Input Source Selector * Tuner/CD/Aux/Phono Input RCA Jacks * Tape Monitor Switch * 110/220 Voltage Switchable * Rack Mount Design * Dimensions: 19''W x 2.375''H x 8.5''DAs far as grounding the TT, if you must, just use any screw on the preamp chassis.

Dear Sushant,    I do not think your use of an equalizer has caused any problems.  I will explain the proper use of the source/direct button.  This button's function is to monitor the output of a recorder connected to the record outputs of your amp.  When this button is pressed on the sound going to the speakers comes direct from the "source" (cd, radio tuner, phonograph etc.) when in the off position you can monitor the recording of whatever source is being recorded via the tape deck.  This switch must be off to record through the amps record outputs.    To test this, put a blank tape in the tape deck, choose the source as phono and place the dec in record/pause.  With the source direct button pressed on you should hear a change in volume when moving the amp's volume knob only.  When source direct is off you will be able to hear the output of the tape deck, so adjusting the tape deck's record level will also affect the volume coming out of the speakers.  more record level in/ more level out.!    Below is copied from page 9 of your user operation manual for Marantz's explanation of the source/direct button. 
best of wishes, Michael Mittelsdorf

If you're certain there is no sound going out of the TT...

Setting the Pre-amp Switch
For increased flexibility of use, this turntable has an internal
stereo phono pre-amplifier. The Pre-amp Selector Switch
is located under the turntable platter, in the rear-center
(Fig. 1). If the system amplifier you are using has a PHONO
input, set the Pre-amp Selector Switch to the “OFF”
position. If your amplifier does not have a PHONO input,
set the Pre-amp Selector Switch to the “ON” position and
connect the turntable’s output cables to the AUX or other
high-level input on the amplifier (described later).

Turntable operates, but no sound at all
1. The stylus guard is still in place.
2. The tone arm Lift button is pressed in.
3. Amplifier controls set incorrectly: wrong input selected,
tape monitor on, speakers switched off, etc.
4. Check the stylus on phono cartridge for correct placement.
Refer to the instructions for replacing the stylus
on page 5.
Turntable operates, but no sound, or sound not loud
enough
1. If the turntable is connected to an AUX (high-level)
input: The Pre-amp Selector Switch may be set to the
“OFF” position (phono-input level).
2. The input gain of the amplified speaker or similar
device may be too low.
3. The stylus assembly may not be fully seated in the
cartridge body.

You could also isolate the problem to either the TT or the PC by trying the TT on some other sound device like a receiver. Make sure the PreAmp Selector switch is ON and plug the TT into any AUX, CD or TAPE input.

Thanks guys, but i solved my problem, i experimented and decided that i would run my DVD player (Aux Out) as a CD player through the Equaliser in [Rec] and from equaliser out [Play] i went into Tape Play on Amp, then i connected my Turntable CD Radio System to the Tape 1 Rec on Equaliser and then from Tape 1 Play on Equaliser went into the Tape 2 on AMP then i could use Aux in on Amp to connect my Laptop via my laptops headphone socket my laptop has an equaliser so i didn't need to connect to pioneer EQ, i also connected a small 5.1 to the DVD's 5.1 and connected 4 *45w Speakers to the AMP. and i can say it was FANTASTIC i couldn't get to 5 on my volume it was un @$#%believable.
My Quote
"Where there's an In, there's an Out".

did you turned aux function?

turn off your player by pressing and holding volume controler.
press and hold longer (~5 sec) it again to turn it on (you should see 'tuner' in the lcd).
push up arrow to select aux and right/left to turn it on.

now you can connect your ipod and select aux (as ussual switching between tuner/cd player/aux)

cheers :)