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Advertising Index Altronics.....................37-40, 59, 69 Blackmagic Design....................... 5 Dave Thompson........................ 103 Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar............................. IFC, 11-14 Keith Rippon Kit Assembly....... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 Oatley Electronics..................... 103 OurPCB Australia.......................... 8 PCBWay......................................... 7 PMD Way................................... 103 SC Christmas Decorations......... 51 SC HiFi Headphone Amp............ 36 SC USB-C Power Monitor......... 103 Silicon Chip Back Issues........... 36 Silicon Chip PDFs on USB......... 78 Silicon Chip Shop...................... 15 The Loudspeaker Kit.com............ 6 Wagner Electronics..................... 95 Errata and on-sale date Digital Preamplifier part one, October 2025: in Fig.3 on page 34, the pins of IC7b and IC8b are swapped. The upper pin of each should be pin 5 (+) and the lower pin should be pin 6 (-). The connections of the other op amps in the circuit are correct. Serviceman’s Log, October 2025: the photo at lower left on page 89 is of the wrong computer; it is an Acer, not a Toshiba P750. Next Issue: the January 2026 issue is due on sale in newsagents by Monday, December 29th. Expect postal delivery of subscription copies in Australia between December 29th and January 14th. 104 Silicon Chip go from there, or do you think it may be something else? (E. W., Denistone, NSW) ● We have not heard of this situation before, where the Tweezers worked and then suddenly stopped. It could be the microcontroller, but we also suspect the OLED module, since they can be quite delicate. We have had reports of readers fitting the cell upside-down and thus flattening it, but if you are getting power to the circuit, that is not likely to be the case. One way to tell if it is the microcontroller or OLED at fault would be to see if there are signals getting to the SDA or SCL pins on the display. An oscilloscope should show activity several times per second. We have also used a piezo transducer to ‘listen in’ to data at times, so if you don’t have an oscilloscope, try connecting one temporarily between those pins and GND. If you detect some traffic, that means the PIC is probably OK and the OLED screen may be faulty. If there is no traffic, we would suspect the microcontroller. Another thing worth trying is to reset the micro by briefly shorting pins 1 and 3 of the ICSP header (CON1), taking MCLR to ground. That might force the microcontroller to re-initialise the OLED, in case the two are out of sync. Alternative switch for Signal Tracer The Audio Signal Injector & Tracer project (June 2015; siliconchip.au/ Article/8603) lists a DP4T slide switch from element14. This switch is no longer made. Can you suggest a replacement? (E. M., Capel, WA) ● Altronics Cat SX2040 is a suitable alternative (www.altronics.com.au/p/ sx2040-dp4t-pcb-mount-miniatureslide-switch). Fixing Playmaster amplifiers In the late 1990s, I bought kits for the Playmaster Series 4 preamplifier, Playmaster 300W Subwoofer Amplifier and three of the Jaycar Playmaster Pro Series 3 Power Amplifier from Jaycar in Clayton, Melbourne. I recently replaced the four electrolytic capacitors in the Pro Series 3 Power Amplifiers after noticing odd behaviour in the sound. The capacitors Australia's electronics magazine were leaking and needed replacement. I sourced replacement capacitors from Jaycar in North Lakes, Queensland. Yesterday, I had another setback. It appears the 300W Subwoofer had a catastrophic failure of the power amplifier Mosfets. Unfortunately, it took out the connected subwoofer as well. I have not yet disassembled the amplifier. Since I do not have the assembly instructions anymore, can you provide the assembly instructions and circuit diagrams? As I recall, the instructions had various voltage check test points documented in the instructions. Do you have or know of a source of replacement Mosfets? I have really enjoyed the setup in my office with this equipment and would like to continue use if possible. (S. W., North Brisbane, Qld) ● We don’t have access to Jaycar’s kit instructions, and after around 30 years, we doubt they would still have them. They would have been based on the articles published in Electronics Australia: December 1996 & January 1997 for the Series 4 preamplifier, April & May 1995 for the 300W Subwoofer and February & March 1994 for the Pro Series 3 Power Amplifier. Scans of these articles are available from our website for the preamp: siliconchip.au/Shop/15/3980 siliconchip.au/Shop/15/3981 And for the subwoofer: siliconchip.au/Shop/15/3244 siliconchip.au/Shop/15/3441 Lastly, the power amplifier: siliconchip.au/Shop/15/6640 siliconchip.au/Shop/15/6641 Replacement Mosfets are available from Jaycar (N-channel) and DigiKey (P-channel). There are other suppliers if you search for the parts online: www.jaycar.com.au/p/ZT2460 www.digikey.com.au/en/products/ detail/2SJ162-E/1244174 There appear to be three Mosfets for each half of the amplifier, so you will need three 2SK1058s and three 2SJ162s. Check the circuits for anything else you may need before ordering anything. Since you will have to back-order the 2SJ162s, we suggest you do that first. The estimated delivery date is early next year. The manufacturer will stop making 2SJ162s in March 2026. Be careful ordering the 2SJ162s from other stores as there appear to be counSC terfeits on the market. siliconchip.com.au