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Whaam68 2nd Feb 2020 2:03 pm

2P1M 7Y SCR equivalent
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Iím slowly working through the mechanism power supply board of an early 1980s TEAC A300 cassette deck (see thread on page 2 of the tape sub forum) - attempting to solve the lack of power to the mechanism. All the diodes so far have been ok but Iíve just tested the SCR a 2P1M. With my meter on the 20k range and negative on the anode and positive on the cathode (per the datasheet pinout) Iím reading O/C rather than high resistance. Doctor google suggests that this is a bad thing! Can I replace this with any TO-202 SCR with a 4A 100v rating? Can anyone recommend a common substitute.

Supplemental question what is likely to have caused the failure? Assuming my conclusion above is right!

G6ONEDave 10th Feb 2020 4:26 pm

Re: 2P1M 7Y SCR equivalent
Re the SCR test reading. If this is a thyristor then you should not get any resistance reading between the anode and cathode when out of circuit, you will however get a low reading between the gate and anode, which may be the same both ways round. If the thyristor is showing a dc resistance between anode and cathode when in an off state (such as out of circuit) it is faulty. The same is generally true for a triac. These devices conduct when a drive signal is presented to the gate.. Check the volts on the cathode when powered to see if you have anything. If not check input volts on the anode and if there is a correct voltage there either you don't have any gate drive signal or if unlucky the thyristor has gone o/c so won't conduct. The anode input may be an output if the supply is a negative one. Sorry don't have a circuit to hand, so don't know which way round your device is connected. If the gate drive is missing, have look for a diac in the circuitry (BR100), it looks like a signal diode with a black band round it's centre, unfortunately the diac won't give a resistance reading either way round unless it is faulty, so you will have to substitute it for a powered test. Hope this helps out, otherwise a circuit would be useful to help diagnose the problem.

Diabolical Artificer 11th Feb 2020 6:48 am

Re: 2P1M 7Y SCR equivalent
You could try any SCR with similar ratings but I use C106D's a lot, cheap and easy to find.


McMurdo 11th Feb 2020 9:44 am

Re: 2P1M 7Y SCR equivalent
open circuit both ways between anode and cathode, low resistance (few tens of ohms) between cathode and gate.
I've just checked some thyristors in the drawer and they measure the same whether AVO or digital (not on diode check).

Sometimes the c-g reading will read slightly differently depending on polarity.

If in doubt, wire it up with a small bulb and a gate resistor.

G6ONEDave 11th Feb 2020 3:45 pm

Re: 2P1M 7Y SCR equivalent
Thanks McMurdo, don't know where my head was but I did get the anode and cathode re the gate resistance check and output the wrong way round. Perhaps Mike could post some voltage readings and a schematic so that more help could be offered to solve his problem. Dave

TrevorG3VLF 16th Feb 2020 12:05 am

Re: 2P1M 7Y SCR equivalent
I bought some SCRs some time ago from Bowood Electronics, I think they were labeled 1P1M. Similar to C106D but cheaper.
The site is down at the moment but you could ring him.

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