TA7136AP replacement adapter - HOW TO USE
The assembled board
Assemble the TA7136AP replacement adapter kit with the provided parts. The 0.1" edge pins can be mounted either way, depending on the application's space constraints and the op amp package you are using SOIC-8 vs DIP-8.
How to use this adapter:
Sansui TU-9900:
- VERY IMPORTANT !!! Remove C07, C08 (56pF) & C19, C20 (100pF) on the multiplex board (F-2526). These parts are necessary ONLY for the original Toshiba TA7136AP part, leaving them in place WILL affect the operation of the TA7136AP replacement adapter.
- remove the original TA7136AP (IC01 & IC02)
- the TA7136AP adapter board have provisions for a DC bypass via two 0603 SMD capacitor footprint. These footprints have their ground tied together and the remaining end to pins 4 and 7 respectively of the new op amp. Included with the TA7136AP replacement adapter kit are eight 0603 AVX 100nF/25V X7R ceramic capacitors. The extras are in case you loose some while assembling the kit;) These lower value caps are for taking care of the high frequency bypassing while the higher value electrolytic capacitors mentioned below will take care of the lower frequency spectrum.
- on the adapter board, a plated through-hole is provided near pin 1 for hooking up the adapter board ground plane, use a solid bare wire ~22AWG as a jumper (L-shaped) from the hole to pin 1 on either side of the adapter board. The trimmed off leads from the high-value electrolytic capacitors you'll be installing below will fit nicely. This jumper has one end soldered to the hole near pin 1 and other end tack soldered to pin 1 of the adapter board. Make sure the 0.1" edge pins provided are in place before soldering the ground jumper. Another method is to scratch off the solder mask near pin 1 and the hole and put a solder blob instead. It is necessary to do this since the original solder mask opening of the adapter board was not sufficiently open to allow a solder blob. Future design will address this issue once the original adapter boards gets depleted :)
- on the multiplex board (F-2526), to complete the ground circuit for the adapter, add a couple of ~22AWG stranded wires near pin 1 of IC01 & IC02 where C07 and C09 were connected. The other end of the two separate wires should go the near R17's end tied to the chassis/ground. Other ground points can be used as long as they are not near the return path of the inverting input feedback signal C05 & C06 (47uf/6.3V).
- note that the TU-9900, surprisingly doesn't have any DC bypass capacitors that are very close to the two TA7136APs. The closest one (C631 10uF/16V)) to IC01 is more than 1" away, even worse for IC02. You need to add 4x high value electrolytic caps ~10-47uF/25V on the solder side (bottom of the board). Low-ESR type like United Chemicon KY, Panasonic FC/FM, Nichicon HE, etc. will work nicely. Failure to add these higher-value electrolytic capacitors will encourage oscillation of the faster op amp you are replacing the TA7136AP with. There is not enough room to add these big capacitors on the adapter boards and the logical location will be the solder side of the multiplex board.
- double check all your connections and component polarities before powering up