Quad 303 pop on switch on - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Boulevardier · 22nd Jun 2022, 12:31 pm

Quote:

Originally Posted by mikes08

I have some spare power transistors both RCA vintage and some new made in Mexico!

If you get around to replacing the output transistors, you really should read this old thread...

https://www.vintage-radio.net/forum/...d.php?t=137769

The "vintage" RCA ones might be OK, but the new "Mexican" ones are likely to be the newer type of 2N3055 - which could prove "life-threatening" to the amp.

Mike

Valvepower · 22nd Jun 2022, 7:05 pm

Hello,

Somewhere at the back of my mind I had 303 which ‘popped’ either when tuned on or off and it was caused by an open circuit diode MR100 or MR101.

This was now 30+ years ago and I may be way off base here and I've got my knickers in a twist

Terry

mikes08 · 23rd Jun 2022, 7:07 am

Carriba!.
Thanks Mike. If i do go that route might source some proper ones from Dada -possibly why i have some spare new ones. I think that is what i did before on another 303 i built with new boards from China some years back - similar to that old thread - possibly ten years now. No access to a scope unfortunately only multimeter.
I should have mentioned - brain fog - once switched on for the first time in the day it doesn't pop on subsequent turn on during the day unless left off for some time - would that point to capacitor charging up for the first time and then depleting if left off for a period of time?
I did post this on the FB Quad group and suggestion is to go over all the joints on the board and re-solder so a job for the weekend.

mikes08 · 27th Jun 2022, 1:25 pm

I reflowed the joints over weekend and no joy so swapped out Tr102 (ZTX304) for a BC546 but was getting some strange voltages (39v instead of 67v across pins 1 and 9 on the board) so swapped back again - voltages normal again. I am looking at two data sheets for the ZTX300 series which show the Emitter and collector transposed so may have fitted the BC546 wrong way round unless the sun got to me over the weekend?

Quiescent all good. Diodes all good.
Does anyone have a definitive configuration - I do tend to go with 'alldatasheet' but it might be wrong?
If that doesn't solve it going to swap out the two power transistors (with genuine RCA spares i have from another 303) as definitely confirmed only right channel affected.

https://alltransistors.com/adv/pdfvi...f&dire=_diodes

https://pdf1.alldatasheet.com/datash...LA/BC546B.html

I could try swapping the boards over and then if the pop stayed in the right channel i know the boards are not at fault.

Petedox · 27th Jun 2022, 1:39 pm

Alldata is correct. I wouldn't swap out the power transistors.

mikes08 · 27th Jun 2022, 1:46 pm

Quote:

Originally Posted by Petedox

Alldata is correct. I wouldn't swap out the power transistors.

Thanks Peter which is odd as that is how I fitted it but will check again.

Any reason you say that Peter? not likely to be where the fault lies?

Mike

Sideband · 27th Jun 2022, 1:47 pm

You need to swap the EC connections over. Always check data sheets when swapping transistors. Some have emitter in the centre, most have collector in the centre but a lot of the 'BC' range have base in the centre. I did a similar thing with an old Akai amp when subbing the pre-drivers. Just had to be careful when using BC638's making sure they were inserted correctly. A transistor data book is invaluable.

mikes08 · 27th Jun 2022, 1:55 pm

Many thanks - I have the circuit diagram so will double check the right legs go the right components on the board first. At least base is the same so i might have 'inverted' it. I have done it before and a quick swap round sorted it

Petedox · 27th Jun 2022, 1:58 pm

If, after swapping the EC connections over you still have the fault it is far easier to swap the boards over (18 connections) than to remove the heatsink and faff around replacing the output transistors. I would view this as a last resort after thoroughly investigating the board.

mikes08 · 27th Jun 2022, 4:33 pm

Thanks Pete.
I know what you are saying. I have done one before on a 303 when i re-built one but will start with the easy option first and eliminate the boards as a source of the problem.

Ted Kendall · 27th Jun 2022, 4:52 pm

Could this be momentary instability? Are the output transistors to spec?

mikes08 · 30th Jun 2022, 7:19 am

Replaced TR 102 and no change so next is to swap the boards over and if the 'pop' stays in the right channel will investigate the output transistors.

mikes08 · 3rd Jul 2022, 8:47 am

Swapped the boards over yesterday and the 'pop' on turn on remains in the right channel which leads me to think the problem lies with the power transistors - right channel are the top two on the heatsink. I have two spare RCA ones which i saved from another 303 when i rebuilt that with modern boards and changed all five TR's on the heatsink with those supplied from Dada so that is my next plan. I have had a meter on them in diode mode and the readings don't look amiss but i guess as switched on one could go wobbly?
As stated the amp works fine once switched on. The main capacitors were all changed from the recent Dada kit upgrade but i suppose it is not impossible one of those could be faulty from new.
Anywhere else i could look?
KR
Mike

stevehertz · 3rd Jul 2022, 8:57 am

Quote:

Originally Posted by mikes08

The main capacitors were all changed from the recent Dada kit upgrade but i suppose it is not impossible one of those could be faulty from new.

Mike

I fitted a brand new faulty cap to a wireless just a few months ago, it happens.

tony brady · 3rd Jul 2022, 9:11 am

I would try swapping the output capacitors over

mikes08 · 3rd Jul 2022, 9:13 am

Quote:

Originally Posted by stevehertz

Quote:

Originally Posted by mikes08

The main capacitors were all changed from the recent Dada kit upgrade but i suppose it is not impossible one of those could be faulty from new.

Mike

I fitted a brand new faulty cap to a wireless just a few months ago, it happens.

Thanks Steve
I could swap those left to right and see if the problems migrates - ten minute job.

Going forward can anyone suggest a reasonable transistor tester that would be worth purchasing?
Alternatively a second hand oscilloscope though would have to learn how to use?

nutteronthebus · 3rd Jul 2022, 10:18 am

I use one of these and found out that the transistors go low gain / nsy with age https://www.peakelec.co.uk/acatalog/...-analyser.html

Craig Sawyers · 3rd Jul 2022, 11:41 am

Peak are a great company. I used a DCA55, but eventually bought a DCA75, which does curve tracing too. Out of stock alas, although the DCA55 is in stock.

Craig

mikes08 · 3rd Jul 2022, 3:32 pm

How odd! I swapped the output capacitors over (Epos 10,000mf from Dada) and hey presto, the pop on turning on had migrated to the left channel. Yes I thought, might have a dodgy capacitor after all so i swapped both out for some new spare Denon 12,000mf capacitors i had but not used previously.
Oh poop - the pop is still in the left channel on turn on.
What am i missing please?

Aub · 3rd Jul 2022, 4:13 pm

Dodgy Denon cap? Try swapping those around perhaps?

Aub

22nd Jun 2022, 7:05 pm	#22
Valvepower Octode Join Date: Aug 2008 Location: Rayleigh near Southend-On-Sea, Essex, UK. Posts: 1,878	Re: Quad 303 pop on switch on Hello, Somewhere at the back of my mind I had 303 which ‘popped’ either when tuned on or off and it was caused by an open circuit diode MR100 or MR101. This was now 30+ years ago and I may be way off base here and I've got my knickers in a twist Terry

23rd Jun 2022, 7:07 am	#23
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on Carriba!. Thanks Mike. If i do go that route might source some proper ones from Dada -possibly why i have some spare new ones. I think that is what i did before on another 303 i built with new boards from China some years back - similar to that old thread - possibly ten years now. No access to a scope unfortunately only multimeter. I should have mentioned - brain fog - once switched on for the first time in the day it doesn't pop on subsequent turn on during the day unless left off for some time - would that point to capacitor charging up for the first time and then depleting if left off for a period of time? I did post this on the FB Quad group and suggestion is to go over all the joints on the board and re-solder so a job for the weekend. Last edited by mikes08; 23rd Jun 2022 at 7:14 am.

27th Jun 2022, 1:25 pm	#24
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on I reflowed the joints over weekend and no joy so swapped out Tr102 (ZTX304) for a BC546 but was getting some strange voltages (39v instead of 67v across pins 1 and 9 on the board) so swapped back again - voltages normal again. I am looking at two data sheets for the ZTX300 series which show the Emitter and collector transposed so may have fitted the BC546 wrong way round unless the sun got to me over the weekend? Quiescent all good. Diodes all good. Does anyone have a definitive configuration - I do tend to go with 'alldatasheet' but it might be wrong? If that doesn't solve it going to swap out the two power transistors (with genuine RCA spares i have from another 303) as definitely confirmed only right channel affected. https://alltransistors.com/adv/pdfvi...f&dire=_diodes https://pdf1.alldatasheet.com/datash...LA/BC546B.html I could try swapping the boards over and then if the pop stayed in the right channel i know the boards are not at fault. Last edited by mikes08; 27th Jun 2022 at 1:35 pm.

27th Jun 2022, 1:39 pm	#25
Petedox Pentode Join Date: Feb 2020 Location: Waterlooville, Hampshire, UK. Posts: 200	Re: Quad 303 pop on switch on Alldata is correct. I wouldn't swap out the power transistors. __________________ Pete BVWS Member

27th Jun 2022, 1:47 pm	#27
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,567	Re: Quad 303 pop on switch on You need to swap the EC connections over. Always check data sheets when swapping transistors. Some have emitter in the centre, most have collector in the centre but a lot of the 'BC' range have base in the centre. I did a similar thing with an old Akai amp when subbing the pre-drivers. Just had to be careful when using BC638's making sure they were inserted correctly. A transistor data book is invaluable. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

27th Jun 2022, 1:55 pm	#28
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on Many thanks - I have the circuit diagram so will double check the right legs go the right components on the board first. At least base is the same so i might have 'inverted' it. I have done it before and a quick swap round sorted it

27th Jun 2022, 1:58 pm	#29
Petedox Pentode Join Date: Feb 2020 Location: Waterlooville, Hampshire, UK. Posts: 200	Re: Quad 303 pop on switch on If, after swapping the EC connections over you still have the fault it is far easier to swap the boards over (18 connections) than to remove the heatsink and faff around replacing the output transistors. I would view this as a last resort after thoroughly investigating the board. __________________ Pete BVWS Member

27th Jun 2022, 4:33 pm	#30
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on Thanks Pete. I know what you are saying. I have done one before on a 303 when i re-built one but will start with the easy option first and eliminate the boards as a source of the problem.

27th Jun 2022, 4:52 pm	#31
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Quad 303 pop on switch on Could this be momentary instability? Are the output transistors to spec?

30th Jun 2022, 7:19 am	#32
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on Replaced TR 102 and no change so next is to swap the boards over and if the 'pop' stays in the right channel will investigate the output transistors.

3rd Jul 2022, 8:47 am	#33
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on Swapped the boards over yesterday and the 'pop' on turn on remains in the right channel which leads me to think the problem lies with the power transistors - right channel are the top two on the heatsink. I have two spare RCA ones which i saved from another 303 when i rebuilt that with modern boards and changed all five TR's on the heatsink with those supplied from Dada so that is my next plan. I have had a meter on them in diode mode and the readings don't look amiss but i guess as switched on one could go wobbly? As stated the amp works fine once switched on. The main capacitors were all changed from the recent Dada kit upgrade but i suppose it is not impossible one of those could be faulty from new. Anywhere else i could look? KR Mike

3rd Jul 2022, 9:11 am	#35
tony brady Hexode Join Date: Mar 2014 Location: Peacehaven, East Sussex, UK. Posts: 278	Re: Quad 303 pop on switch on I would try swapping the output capacitors over

3rd Jul 2022, 10:18 am	#37
nutteronthebus Hexode Join Date: Jun 2011 Location: Glossop, Derbyshire, UK. Posts: 487	Re: Quad 303 pop on switch on I use one of these and found out that the transistors go low gain / nsy with age https://www.peakelec.co.uk/acatalog/...-analyser.html __________________ Any tool can be used as a hammer but a screwdriver makes the best chisel

3rd Jul 2022, 11:41 am	#38
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,980	Re: Quad 303 pop on switch on Peak are a great company. I used a DCA55, but eventually bought a DCA75, which does curve tracing too. Out of stock alas, although the DCA55 is in stock. Craig __________________ Doomed for a certain term to walk the night

3rd Jul 2022, 3:32 pm	#39
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 133	Re: Quad 303 pop on switch on How odd! I swapped the output capacitors over (Epos 10,000mf from Dada) and hey presto, the pop on turning on had migrated to the left channel. Yes I thought, might have a dodgy capacitor after all so i swapped both out for some new spare Denon 12,000mf capacitors i had but not used previously. Oh poop - the pop is still in the left channel on turn on. What am i missing please?

3rd Jul 2022, 4:13 pm	#40
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,038	Re: Quad 303 pop on switch on Dodgy Denon cap? Try swapping those around perhaps? Aub __________________ Life's a long song, but the tune ends too soon for us all.