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Inside - Unison Research SR1 amp

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I picked this up from Dallas Clarke almost a month ago written off as a non economical repair, I'm using this to help repair another of my clients unit. AS usual UR will not give out a service manual nor will Radiance who is the Australian distributor UR audio components understandable but this is a EOL/discontinued model if they are really that afraid of schematics floating around I can easily trace the circuit with a reverse engineered schematic and post it on diyaudio or hifiengine. There suggestion is I send the unit to Carlton Visual to get it repaired and have them most likely charge me half a leg to repair it when I can repair it myself.


Anyway waiting for the secondary winding fuses to show up. Supposedly one channel blown mos who knows.


Amp in question:


From Google.






Some proprietary schit right here:








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Very pretty, but only the first image is showing for me.

All others are blocked.

Probably my ad blocker I'm guessing.

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Sorry nope.

disabled ad blockers etc, still nothing.

I've this problem before but just ignored it.

oh well. its my problem i suspect :)


where are the first and subsequent images hosted ?

never mind. photobucket, that explains it, i have issues with them at the best of times......

Edited by Green Wagon

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With my SRA-3S finished. Have started work on this. Currently on hold while my order is being shipped. So Unison Research decided I either take it to Carlton AV to get it repaired through them (since they are the Unison Research distributor here) and pay a small fortune for something I can fix or get help from Tessio of UR's support department. So before I can troubleshoot whether the output stage mosfet IRFP 9240 and 240 pairs are blown on one channel, the amp blows fuses meaning a short in the amp, either a resistor or diode or the mosfet's or even a shorted capacitor.


So consulting with Tessio since I cannot be given a service manual or even schematic, his suggestion was to check the 24v 1watt zener diodes D2 and 6 on the PCB. I measured them and sure enough D6 gave me 0.00001 for diode test and anode/cathode vice versa resistance check on my DMM, this is a short rather then being open. I asked Tessio what could be the problem to these giving out and better to fix the problem then to replace it and have it short the zeners again, he suggested that they could've been overdriven from the amp being pushed to hard or heat. So I've gone for some On Semi 1N5359 24v but 5watt rated zener diodes. Had to dis-assemble most of the amp to get to the circuit board. Not really hard but pretty modular too


Some internal pics:






Black marked lines indicate where the new zeners will go since the 5 watt replacement is bigger so needs to be mounted on the trace side. Easier to de-solder too if it goes to schit again














Will post an overall shot sometime tomorrow. 

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Bzx85c24 zener diodes out. 1n5359b in. Troubleshooting nightmare so far.

Replacement caps ordered consisting of Kemet esh, elna silmic 2, panasonic nhg, nichicon and philips bc.

Irfp9240 and 240 fets removed. Remounted zeners d2 and d6 with shorter lead length.

Transformer clusterfk problem caused by Dallas Clark rectified. Pass inductance resistance test but anomaly on the 100v winding. Currently wired for 120v withtime delayed 6.3amp slowblo no fuse blowout. Amp doesn`t power on 100v winding when adjusted. Overdrive led on right clip at 0.612% thd and left at 0.89%. Scratching my head atm...

Sent from my LG-D855 using Tapatalk

Edited by DefQon

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More problems. Soldered in new output mosfets. Powered amp on, no more solid red light as it was the amp was showing an orange led, meaning warming up the 12AU7's. Next minute amp goes to red light mode again with both channel's overdrive led on. Powered it off and discovered I forgot to put the protection circuit module in. Amp won't power on now. Fuse intact, but silicon rectifier bridge KBPC2510W measures open on 3/4 leads. Going to test again. 


EDIT 1: I guess by not using the protection module board one of the W10M 1000v 1.5amp rectifier bridge took the overload on power-up, thus momentarily exceeding the 1.5A rated current, because from just a diode test, half wave rectification shows OL on my meter, i.e. an open result rather then a value between 400-600 which by placing the negative lead on the positive side of the bridge shows 596, but positive diode on negative pin of the bridge tested on the other two AC points show OL. 


The KBPC2510W measures perfectly as does the other 2 W10M rectifiers. The designer could've gone with a relay to dis-engage when an over-current is imminent through a passive monitor circuit. 


Culprit (most far right W10M):







More to come when I get the parts in. Seem's ebay is my only option, no other places carry the W10M.


EDIT2: Nope nada, seems that my dmm was playing up before, diodes test perfect. 

Edited by DefQon

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Hi, I am reviving this topic with a question : I am in need of the volume potentiometer, what exactly is the model? I know it's an ALPS.



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