Replacing the Intellivision RF Modulator


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Why I Had To Learn To Do This

Skip this crap and gimme the info!

I don't know about you, but I find it incredibly irritating to play Astrosmash or Buzz Bombers with interference caused by certain sound effects. I noticed that a majority of my Intellivision consoles (I'm a sicko who has many variants - Sears, Sylvania, Tandyvision, etc.) suffered video interference when playing certain games. This problem can become distracting and irritating enough to actually warrant a repair!

Note! Often times, the problem is less severe on one channel. So before proceeding, check to see if your system works better on the other channel setting. It's a lot easier than replacing the part!



This problem is extremely easy to identify if you have a working Intellivision and one of the following two cartridges:

  • Astrosmash
  • Buzz Bombers

For me, Buzz Bombers has always been the best and easiest test case. Simply start the game. When you "fire" a shot of spray from the spray can, you will see noticeable interference on your screen. In some units, this can be quite drastic. In Astrosmash, the "tshh tshh" background tapping sound effect also will cause interference on the screen. If you see this, your RF unit has decayed and you may want to consider replacing it.

If you have a "dead" system that doesn't produce a picture at all, a dead RF unit may or may not be the problem. You may need to remove the RF unit and test it, or try to tap the video and audio signals directly to see of the logic board is producing the correct raw signals sent into the RF unit.



To replace your RF Modulator, you'll need the following items.

Tools & Supplies

  • Soldering iron with a small, narrow tip, and larger, flatter tip (any basic model will suffice)
  • Desoldering braid
  • Desoldering tool (slurps up melty solder)
  • Solder suitable for electronics
  • Philips screwdriver
  • Needle-nose pliers
  • Possibly 1/4" Hex Nut driver (some Master Components used hex-head screws internally)
  • Multimeter (capable of measuring up to 20 V DC and continuity)

Parts



DISCLAIMER: Do this at your own risk! It worked for me. I'm assuming you've got some familiarity with the guts of an Intellivision, and can handle a soldering iron and the tools involved here.

This repair is described for a "standard" Intellivision (i.e. any version except for the Intellivision II). There is no reason why it shouldn't work just as well on an Intellivision II.

  1. Open the Intellivision Console
    Follow this link for step-by-step instructions.

    Intellivision Internals (RF modulator highlighted)

  2. Remove the Defective RF Modulator
    Use the large soldering iron tip, the desoldering tool and the desoldering braid to remove the old RF unit. Start from the "bottom" side of the board - i.e. the side with all the pins sticking out of it. There are four slots arranged in a diamond pattern, and four wires from the modulator itself. There is a lot of solder on the four slots - use a desoldering tool to assist in removing this material. Also, some of the metal tabs inserted through the slots may be twisted slightly to firmly hold the RF modulator in place on the board, in addition to the solder points. Use a needle-nose pliers to assist in bending such tabs so they fit up through the slots in the logic board. Use a small solder tip to desolder the wires.

    The RF modulator looks something like this on the component side of the board.

    UM 1285-8 RF Modulator Unit

    Note: Be extremely careful to avoid inadvertently shorting two connections together when melting and removing the solder - especially on the component side of the board. This will cause endless nightmares when you attempt to use your system again.

    Tip: Remember, when removing solder, lay the desoldering braid over the solder, and put the tip on the solder wick.

    Note: Due to the age of the printed circuit board (PCB) your Intellivision uses as its substrate, be careful when pulling pins to avoid pulling up the actual circuit traces printed on the board. If you do damage an eyelet around a hole, or pull up a trace, you can use a small bit of wire (such as a strand from telephone or CAT-3 or CAT-5 Ethernet cable) to solder a jumper to another solder point.

  3. Install the New RF Modulator
    The part is actually installed "upside down" - i.e. the same way as the main chips on your logic board. If you've done a clean job of removing the solder from the bottom connection slots and the four wire holes, inserting the new part should be simple. Use the needle nose pliers to twist at least two of the tabs (not too much!) that come through the slots on the logic board to hold the unit in place. It may take a bit of patience to aim the four wires into the holes on the logic board.

  4. Test Continuity
    To make sure your handiwork has been successful, use an Ohmmeter to verify that the four wires are properly connected to the main logic board.

  5. Test the RF Modulator
    Assuming no other damage has been incurred, put the logic board back into its metal housing (not necessary on Intellivision II), reconnect the cables, and try out a game. If you need to reset your unit, use a pencil to push the reset switch. If your machine doesn't work, double-check the continuity and the connections to the power conditioning circuit. Also, verify the voltages being supplied.

  6. Reassemble the Unit
    Assuming you've succeeded in restoring your Intellivision, I'd suggest closing up the logic board again, then putting the unit back together. Voila!

    Note: If you do not properly and securely close the metal case around the guts, you may still notice that the resulting picture sent to your TV suffers some interference. This interference is not due to the fire button being pressed, but more just a general image degradation.


An exact replacement part can be purchased at Alltronics. It costs around $4.95 + shipping. Alltronics has a minimum order of $15.00.

Specific Part Information:

Item Name: VHF Intercarrier Vestigial Sideband Modulator
Manufacturer Part Number: UM1285-8
Vendor: ASTEC
Part Number: 92V017

Follow this link for the page where the part lives.

If that doesn't work, I did the following search at their site:

Keywords: modulator

So far, this is the only place online that I could locate this part. I don't the part is at risk of becoming obsolete and out of stock - but it seems that Alltronics specializes in castoff or older parts, whether overstock or what, I don't know. If you find another vendor offering this replacement part, please let me know, and I'll update these instructions put your info here if you'd like.