"ODEP" crown macrotech

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   kedwardsleisure.
I removed a fair few transistors from the main board R.CH and measured the gains , A few were low compared to others of the same number. Some were 2 thirds lower. 2N4123's mostly. I'm in the middle of changing them. Will the MPSA work in place of the MPSW. 42 ,92. Those are 1w ,new ones are .625w. I might put the old ones back in and see what happens. They seem OK. 2961 and MTS105 are still on the board. I might aswell check them all.
I'll check the other parts too. Not been at it for a week.
I changed all the diodes on the Output board. I did that on both a good while back.
Cheers

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Coded Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 03 March 2010 Location: London Status: Offline Points: 18	Post Options Post Reply Quote Coded Report Post Thanks(0) Quote Reply Posted: 08 October 2025 at 9:00pm
	kedwardsleisure. I removed a fair few transistors from the main board R.CH and measured the gains , A few were low compared to others of the same number. Some were 2 thirds lower. 2N4123's mostly. I'm in the middle of changing them. Will the MPSA work in place of the MPSW. 42 ,92. Those are 1w ,new ones are .625w. I might put the old ones back in and see what happens. They seem OK. 2961 and MTS105 are still on the board. I might aswell check them all. I'll check the other parts too. Not been at it for a week. I changed all the diodes on the Output board. I did that on both a good while back. Cheers

kedwardsleisure Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 5157	Post Options Post Reply Quote kedwardsleisure Report Post Thanks(0) Quote Reply Posted: 08 October 2025 at 11:58pm
	dont worry about gains, leave them be. If they test as transistors they'll be ok.
	Kevin North Staffordshire

shaun1264 Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 06 September 2013 Location: Surrey Status: Offline Points: 325	Post Options Post Reply Quote shaun1264 Report Post Thanks(0) Quote Reply Posted: 09 October 2025 at 7:12am
	Hi. You posted about this amplifier over in diyaudio and I tried to help you there. You get very hung up about transistor gain... Not sure why. Gain is not relevant. You need to forget about transistor gain and focus on shorts, change of resistor values or burn out, broken traces, dry joints and even wrong component selection. It seems you are changing many components without actually knowing the problem. This can lead to even more complications and even worse outcome. Don't power it up on full mains. . DBT and Variac needed to prevent further damage! Have you got 15v supply rails to all opamps and -15v low side Q216 predriver collector. Are you sure you put the bias string diodes in the right way and right diodes? Check and check again your work. Transistor's in the right places? NPN and PNP not mixed up? Over at diyaudio you had pictures of two blown resistors with a description of "Those two transistors are the + and - drive on those wires". No idea what you mean by that ... Edited by shaun1264 - 09 October 2025 at 7:17am

DjLeco Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 21 April 2009 Location: Bucharest Status: Offline Points: 820	Post Options Post Reply Quote DjLeco Report Post Thanks(0) Quote Reply Posted: 16 October 2025 at 12:20pm
	@ EmPro: Those are originals ones, on those models the output devices are not 250Watts ones, but lower power ones (150W maybe). That's what they used on powertech and powerbase models (1,2,3). Replace all output devices with MJ15003 MJ15004 if the amp is suppled at max 100Vdc (1 and 2 series), measured on main capacitors after rectifier bridge or with MJ21193 MJ21194 if there's around 115Vdc (3 series). Also replace all 0.2 ohms 5W resistors and B-E resistors of output devices. If need schematics, here I have uploaded all my Crown schematics and service manuals (diamond and gold mine)! https://limewire.com/d/F6tHK#MkckZPNtjY Link expires in 6 days, I hope to see this post until link expires! Good luck! Edited by DjLeco - 16 October 2025 at 12:33pm
	I'm A Stupid SMART Romanian...

EmPro Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 26 June 2020 Status: Offline Points: 992	Post Options Post Reply Quote EmPro Report Post Thanks(1) Quote Reply Posted: 16 October 2025 at 1:19pm
	Already downloaded the pack,cheers (mersi mult domnu).
	EmPro Audio

Coded Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 03 March 2010 Location: London Status: Offline Points: 18	Post Options Post Reply Quote Coded Report Post Thanks(1) Quote Reply Posted: 17 October 2025 at 4:26pm
	DJLeco turned up. shaun1264. Have you got 15v supply rails to all opamps and -15v low side Q216 predriver collector. Yea Are you sure you put the bias string diodes in the right way and right diodes? Check and check again your work. Yea Transistor's in the right places? NPN and PNP not mixed up? Yea All OK man. < ="text/" media="print">#s3gt_translate_tooltip_mini { display: none !important; }

Coded Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 03 March 2010 Location: London Status: Offline Points: 18	Post Options Post Reply Quote Coded Report Post Thanks(0) Quote Reply Posted: 17 October 2025 at 4:27pm
	I was doing some testing yesterday and found that the right pins of Q01 and Q05 on the output boards are grounded on the left channel but not on the right. I changed them for new ones ,thought I might aswell. But ,no change. I was trying find out why the channels are different haven't worked it out yet. I was getting different readings with reference to ground on the multimeter. Edited by Coded - 17 October 2025 at 4:30pm

Coded Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 03 March 2010 Location: London Status: Offline Points: 18	Post Options Post Reply Quote Coded Report Post Thanks(0) Quote Reply Posted: 17 October 2025 at 4:40pm
	I feel like I'm getting somewhere a little bit as I'm looking for a fault or two ,or differences between the two channels. Amp off is the way to go I think. For now anyway.