Re: Source for replacement caps in H744 regulators
On 1/7/2022 2:35 PM, Nigel Johnson Ham via cctalk wrote: I told the chief engineer that the problem was the same thing that caused planes to crash, and he suggested maybe the cargo door had fallen off! (that puts it in 1972 since it was AA Flight 96 that had just happened!) My uncle worked for McDonnell Douglass as an engineer and my dad told me that he got called back to work on that DC 10 door issue. JRJ
Re: Source for replacement caps in H744 regulators
> The terminal posts are aluminum, and can develop an oxide > layer that prevents good contact. > > Removing and replacing them might improve the contact. I have experienced this personally with TO-3 regulators, too. I had a bunch of triple voltage Power One linear supplies that would intermittently brownout, had to chase the threads in the TO-3 sockets (which served as a case terminal connection) and put toothed washers under the screws to bond the TO-3 aluminum case. Thanks, Jonathan
Re: Source for replacement caps in H744 regulators
On 1/7/22 2:21 PM, Rob Jarratt via cctalk wrote: Weirdly, the whine has disappeared. This is after I put the suspect capacitors back in. Because I had previously removed them for reforming, I wonder if one of them was not properly screwed in? The terminal posts are aluminum, and can develop an oxide layer that prevents good contact. Removing and replacing them might improve the contact. Jon
Re: Source for replacement caps in H744 regulators
I never had this problem with an H744 power regulator, but once I had a horrible intermittent problem in the RK05 power supply where the caps were 'wafting in the breeze' of the fan. Metal fatigue had created almost microscopic cracks around the part of the land where the screws attached, causing a disk fault every week or so. It was in one of four drives and the only way I found it was to swap the drives one by one and wait, since the emerg signal was paralleled! I told the chief engineer that the problem was the same thing that caused planes to crash, and he suggested maybe the cargo door had fallen off! (that puts it in 1972 since it was AA Flight 96 that had just happened!) Try reheating around the screws. cheers, Nigel Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU Amateur Radio, the origin of the open-source concept! Skype: tilbury2591nw.john...@ieee.org On 2022-01-07 15:21, Rob Jarratt via cctalk wrote: Weirdly, the whine has disappeared. This is after I put the suspect capacitors back in. Because I had previously removed them for reforming, I wonder if one of them was not properly screwed in? Regards Rob -Original Message- From: cctalk On Behalf Of Jay Jaeger via cctalk Sent: 07 January 2022 16:02 To:cctalk@classiccmp.org Subject: Re: Source for replacement caps in H744 regulators On 1/6/2022 7:03 PM, W2HX via cctalk wrote: My 2c. I am not familiar with a "whine" but certainly a "hum." Sometimes if a power supply has seen a lot of heavy load over its lifetime, the heat generated can begin to do things to the transformer. And once that heat has done its "thing" to the transformer, it stays that way. And no replacing external components will change the hum. However, there are some transformers with bolts and nuts that hold the laminations together. Sometimes they can be tightened to reduce the hum. I don’t know this PS specifically and whether it falls into this category or not. I don’t know if what you are hearing is transformer hum, but if it is, you may just have to live with it. 73 Eugene W2HX Subscribe to my Youtube Channel: https://www.youtube.com/c/w2hx-channel/videos This does not fall "into this category". This is typically high frequency (in excess of 10KHz) whine, not 60 cycle, 120 cycle or even 400 cycle "hum". My experience with many PDP-11 machines going back to the mid 1970s, and those in my collection, is that this whine from the *switching* power supplies is very common. For some people, it may be above the frequency that they can hear. For me it is not (I could also hear burglar alarms in excess of 20KHz back in the day, though I doubt I could now, at age 70.) My *guess* is that it comes from the inductors in the switching circuit, and is *mechanical*, induced by the switching waveform, which in turn is dependent upon load. If I had one that was really bad, I'd be tempted to put on a glove for insulation and hold those to see if the mechanical pressure made any difference. JRJ
RE: Source for replacement caps in H744 regulators
Weirdly, the whine has disappeared. This is after I put the suspect capacitors back in. Because I had previously removed them for reforming, I wonder if one of them was not properly screwed in? Regards Rob > -Original Message- > From: cctalk On Behalf Of Jay Jaeger via > cctalk > Sent: 07 January 2022 16:02 > To: cctalk@classiccmp.org > Subject: Re: Source for replacement caps in H744 regulators > > On 1/6/2022 7:03 PM, W2HX via cctalk wrote: > > My 2c. I am not familiar with a "whine" but certainly a "hum." Sometimes if > a power supply has seen a lot of heavy load over its lifetime, the heat > generated can begin to do things to the transformer. And once that heat has > done its "thing" to the transformer, it stays that way. And no replacing > external components will change the hum. However, there are some > transformers with bolts and nuts that hold the laminations together. > Sometimes they can be tightened to reduce the hum. I don’t know this PS > specifically and whether it falls into this category or not. > > > > I don’t know if what you are hearing is transformer hum, but if it is, you > may just have to live with it. > > > > 73 Eugene W2HX > > Subscribe to my Youtube Channel: > > https://www.youtube.com/c/w2hx-channel/videos > > This does not fall "into this category". This is typically high frequency (in > excess of 10KHz) whine, not 60 cycle, 120 cycle or even > 400 cycle "hum". > > My experience with many PDP-11 machines going back to the mid 1970s, and > those in my collection, is that this whine from the *switching* power > supplies is very common. For some people, it may be above the frequency > that they can hear. For me it is not (I could also hear burglar alarms in > excess > of 20KHz back in the day, though I doubt I could now, at age 70.) > > My *guess* is that it comes from the inductors in the switching circuit, and > is > *mechanical*, induced by the switching waveform, which in turn is > dependent upon load. If I had one that was really bad, I'd be tempted to put > on a glove for insulation and hold those to see if the mechanical pressure > made any difference. > > JRJ
Re: Source for replacement caps in H744 regulators
On 1/6/2022 7:03 PM, W2HX via cctalk wrote: My 2c. I am not familiar with a "whine" but certainly a "hum." Sometimes if a power supply has seen a lot of heavy load over its lifetime, the heat generated can begin to do things to the transformer. And once that heat has done its "thing" to the transformer, it stays that way. And no replacing external components will change the hum. However, there are some transformers with bolts and nuts that hold the laminations together. Sometimes they can be tightened to reduce the hum. I don’t know this PS specifically and whether it falls into this category or not. I don’t know if what you are hearing is transformer hum, but if it is, you may just have to live with it. 73 Eugene W2HX Subscribe to my Youtube Channel: https://www.youtube.com/c/w2hx-channel/videos This does not fall "into this category". This is typically high frequency (in excess of 10KHz) whine, not 60 cycle, 120 cycle or even 400 cycle "hum". My experience with many PDP-11 machines going back to the mid 1970s, and those in my collection, is that this whine from the *switching* power supplies is very common. For some people, it may be above the frequency that they can hear. For me it is not (I could also hear burglar alarms in excess of 20KHz back in the day, though I doubt I could now, at age 70.) My *guess* is that it comes from the inductors in the switching circuit, and is *mechanical*, induced by the switching waveform, which in turn is dependent upon load. If I had one that was really bad, I'd be tempted to put on a glove for insulation and hold those to see if the mechanical pressure made any difference. JRJ
Re: Source for replacement caps in H744 regulators
On 07/01/2022 02:39, Jon Elson via cctalk wrote: > Yes, the 2nd unit is running at 5 KHz, clearly explaining the noise. > Possibly there is a bad flyback diode, or something causing the > different waveform. > That would be D5 I guess? I did do some checks in this area but I can't remember if I swapped that particular part with the other unit. I did a DC test out of circuit using the bench supply and it seemed to work with no leakage in the reverse direction. Perhaps it only fails when running at full speed? Regards, Matt
Re: Source for replacement caps in H744 regulators
On 1/6/22 6:04 PM, Matt Burke via cctalk wrote: Quiet regulator: http://www.9track.net/posts/h744/h744_ba11_q2e.png Noisy regulator: http://www.9track.net/posts/h744/h744_ts11_q2e.png The yellow trace is the emitter of Q2 (input of L1) and the cyan trace is the output of L1. Q2 seems to be switching partly on then fully on in the noisy regulator. it should of course be fully on or fully off as seen on the quiet regulator. Also the switching frequency seems to be lower. Yes, the 2nd unit is running at 5 KHz, clearly explaining the noise. Possibly there is a bad flyback diode, or something causing the different waveform. Jon
Re: Source for replacement caps in H744 regulators
On 2022-Jan-06, at 4:04 PM, Matt Burke via cctalk wrote: > On 06/01/2022 12:59, Jonathan Chapman via cctalk wrote: >> That said, it's not like replacing them with new will *hurt* -- it just >> might not fix the whine. > > I suspect that it won't fix the problem. Slightly hijacking the thread > here but hopefully in a semi-helpful way. > > I have two of these regulators, one from a BA11K and one from a TS11. > Under the same test conditions the one from the TS11 produces a > significantly louder whining noise than the one from the BA11K. Given > that they are largely the same circuit as the H745 regulators and all > the ones I have are silent in operation I find it hard to believe they > are supposed to be like this. I used to have two more TS11 drives and > they both exhibited the same behaviour. Seems to be a common problem. > > Now, for the one from the BA11K (quiet one) the output capacitors were > completely open (0uF) so I had to replace them. Given that I had the new > capacitors I decided to try them in the TS11 regulator to see if it > would fix the whining noise. It made no difference. > > After some probing with an oscilloscope I found that between the two > regulators there was a very different waveform on the emitter of Q2. > > Quiet regulator: http://www.9track.net/posts/h744/h744_ba11_q2e.png > Noisy regulator: http://www.9track.net/posts/h744/h744_ts11_q2e.png > > The yellow trace is the emitter of Q2 (input of L1) and the cyan trace > is the output of L1. Q2 seems to be switching partly on then fully on in > the noisy regulator. it should of course be fully on or fully off as > seen on the quiet regulator. Also the switching frequency seems to be lower. The intermediate step voltage at Q2.E-L1.input is not Q2 partially on. It's D5 shutting off, as it would do when L1 has discharged and current is no longer flowing in it, and follows from the basic principles of a buck converter. Notice that the step is 5V, i.e. the output voltage. > I tried testing/swapping a few parts between the two regulators, L1, Q2, > Q3, E1. It started out reasonably logical and after several days > descended into a unscientific mess of swapping anything and everything > that could possibly be at fault. I got to the point where I had > eliminated just about every component so I must have overlooked > something. I was hoping to stumble upon the answer and then learn > something from it but so far no luck. This project has been shelved for > a while now.
RE: Source for replacement caps in H744 regulators
My 2c. I am not familiar with a "whine" but certainly a "hum." Sometimes if a power supply has seen a lot of heavy load over its lifetime, the heat generated can begin to do things to the transformer. And once that heat has done its "thing" to the transformer, it stays that way. And no replacing external components will change the hum. However, there are some transformers with bolts and nuts that hold the laminations together. Sometimes they can be tightened to reduce the hum. I don’t know this PS specifically and whether it falls into this category or not. I don’t know if what you are hearing is transformer hum, but if it is, you may just have to live with it. 73 Eugene W2HX Subscribe to my Youtube Channel: https://www.youtube.com/c/w2hx-channel/videos -Original Message- From: cctalk On Behalf Of Matt Burke via cctalk Sent: Thursday, January 6, 2022 7:05 PM To: cctalk@classiccmp.org Subject: Re: Source for replacement caps in H744 regulators On 06/01/2022 12:59, Jonathan Chapman via cctalk wrote: > That said, it's not like replacing them with new will *hurt* -- it just might > not fix the whine. I suspect that it won't fix the problem. Slightly hijacking the thread here but hopefully in a semi-helpful way. I have two of these regulators, one from a BA11K and one from a TS11. Under the same test conditions the one from the TS11 produces a significantly louder whining noise than the one from the BA11K. Given that they are largely the same circuit as the H745 regulators and all the ones I have are silent in operation I find it hard to believe they are supposed to be like this. I used to have two more TS11 drives and they both exhibited the same behaviour. Seems to be a common problem. Now, for the one from the BA11K (quiet one) the output capacitors were completely open (0uF) so I had to replace them. Given that I had the new capacitors I decided to try them in the TS11 regulator to see if it would fix the whining noise. It made no difference. After some probing with an oscilloscope I found that between the two regulators there was a very different waveform on the emitter of Q2. Quiet regulator: http://www.9track.net/posts/h744/h744_ba11_q2e.png Noisy regulator: http://www.9track.net/posts/h744/h744_ts11_q2e.png The yellow trace is the emitter of Q2 (input of L1) and the cyan trace is the output of L1. Q2 seems to be switching partly on then fully on in the noisy regulator. it should of course be fully on or fully off as seen on the quiet regulator. Also the switching frequency seems to be lower. I tried testing/swapping a few parts between the two regulators, L1, Q2, Q3, E1. It started out reasonably logical and after several days descended into a unscientific mess of swapping anything and everything that could possibly be at fault. I got to the point where I had eliminated just about every component so I must have overlooked something. I was hoping to stumble upon the answer and then learn something from it but so far no luck. This project has been shelved for a while now. Regards, Matt
Re: Source for replacement caps in H744 regulators
On 06/01/2022 12:59, Jonathan Chapman via cctalk wrote: > That said, it's not like replacing them with new will *hurt* -- it just might > not fix the whine. I suspect that it won't fix the problem. Slightly hijacking the thread here but hopefully in a semi-helpful way. I have two of these regulators, one from a BA11K and one from a TS11. Under the same test conditions the one from the TS11 produces a significantly louder whining noise than the one from the BA11K. Given that they are largely the same circuit as the H745 regulators and all the ones I have are silent in operation I find it hard to believe they are supposed to be like this. I used to have two more TS11 drives and they both exhibited the same behaviour. Seems to be a common problem. Now, for the one from the BA11K (quiet one) the output capacitors were completely open (0uF) so I had to replace them. Given that I had the new capacitors I decided to try them in the TS11 regulator to see if it would fix the whining noise. It made no difference. After some probing with an oscilloscope I found that between the two regulators there was a very different waveform on the emitter of Q2. Quiet regulator: http://www.9track.net/posts/h744/h744_ba11_q2e.png Noisy regulator: http://www.9track.net/posts/h744/h744_ts11_q2e.png The yellow trace is the emitter of Q2 (input of L1) and the cyan trace is the output of L1. Q2 seems to be switching partly on then fully on in the noisy regulator. it should of course be fully on or fully off as seen on the quiet regulator. Also the switching frequency seems to be lower. I tried testing/swapping a few parts between the two regulators, L1, Q2, Q3, E1. It started out reasonably logical and after several days descended into a unscientific mess of swapping anything and everything that could possibly be at fault. I got to the point where I had eliminated just about every component so I must have overlooked something. I was hoping to stumble upon the answer and then learn something from it but so far no luck. This project has been shelved for a while now. Regards, Matt
Re: Source for replacement caps in H744 regulators
It would be a lot easier to replace the large circular regulator if you're taking the shotgun approach, and much more likely that the regulator is a source of faults. and it's cheaper. For the h744, 45, 54. BUT measuring things is the best way if you can do it. Pull the values from the backplane, there are test points that you can measure from. Bill On Thu, Jan 6, 2022 at 2:30 PM Wayne S via cctech wrote: > So you want to replace capacitors just because they “whine” ? > I’ll say that because you are learning, that is not good troubleshooting > practice. > Make a checklist of troubleshooting power supplies. > There are a lot of good youtube videos and other internet information on > how power supplies work, how to check them and repair them. There is danger > when working with power supplies. > When working on electrical equipment do you know about the “working with > one hand in your pocket rule?” Doing this stuff, videos and reading, is not > overly time consuming and may save your life! > > > > Sent from my iPhone > > > On Jan 6, 2022, at 07:50, Jon Elson via cctalk > wrote: > > > > On 1/6/22 2:52 AM, Rob Jarratt via cctalk wrote: > >> I think I may need to replace the two output capacitors in some of my > H744 > >> regulators. These are screw terminal 6,000uF 10V parts. I have looked on > >> Mouser, Farnell and Digikey and there don't seem to be any available, > and > >> any that are listed are really rather costly. > >> > >> > >> Does anyone know where I might find some, preferably from a reputable > >> supplier. Note that I am in the UK. > >> > >> > > > > Mouser is a good place to find big caps (or at least used to be). You > might have to get "snap in" caps and solder wires to them, that style seems > to be more available. > > > > Jon > > >
Re: Source for replacement caps in H744 regulators
On 1/6/22 2:52 AM, Rob Jarratt via cctalk wrote: I think I may need to replace the two output capacitors in some of my H744 regulators. These are screw terminal 6,000uF 10V parts. I have looked on Mouser, Farnell and Digikey and there don't seem to be any available, and any that are listed are really rather costly. Does anyone know where I might find some, preferably from a reputable supplier. Note that I am in the UK. Mouser is a good place to find big caps (or at least used to be). You might have to get "snap in" caps and solder wires to them, that style seems to be more available. Jon
RE: Source for replacement caps in H744 regulators
> -Original Message- > From: cctalk On Behalf Of Peter Coghlan > via cctalk > Sent: 06 January 2022 12:16 > To: General Discussion: On-Topic and Off-Topic Posts > > Subject: RE: Source for replacement caps in H744 regulators > > > > > >> -Original Message- > >> From: cctalk On Behalf Of Christian > >> Corti via cctalk > >> Sent: 06 January 2022 10:02 > >> To: General Discussion: On-Topic and Off-Topic Posts > >> > >> Subject: Re: Source for replacement caps in H744 regulators > >> > >> On Thu, 6 Jan 2022, r...@jarratt.me.uk wrote: > >> > If I can't find 10V rated ones, then, generally up to what sort of > >> > voltage rating can I go? Of course, physical size will be a factor, > >> > but electrically can it affect operation of the regulator if the > >> > rated > > voltage is > >> too high? > >> > >> If you need to ask this, are you sure you want to do electronics repair? > > > > I am gradually learning. > > > > I'm slowly picking this sort of stuff up as I go along too. > > I think that asking questions like this is the right thing to do when we are not > sure about something and is not at all an indication that someone is > somehow not suited to the task. Quite the reverse in fact. > > If we don't do this sort of work ourselves, it's not going to be easy to get > someone else to do it and make sure it is done well for a > reasonable price. Any contemporary electronics repair outfit, assuming > one can be found, would probably recommend dumping the whole thing and > replacing it with a "modern" power supply. > > > > >> And what makes you think that you need to replace these caps at all? > > > > I appreciate that there is lots of bogus advice out there which suggests that > all capacitors need to be replaced before even starting to investigate the > cause of problems but I think Rob has demonstrated that he is trying to > figure out what is going on rather than just blindly replacing stuff. > > > > > One of the H744 regulators whines and I have been told it could be the > > ESR on these caps. I have measured the ESR on these particular ones > > (out of > > circuit) and it seems higher than the expected values printed on the > > meter and also the ESR is not stable, it fluctuates randomly. This > > suggests the cap is not in great condition. > > > > I guess from that the large capacitance of these units, they are probably > filtering 50Hz or 100Hz ripple and high ESR is probably going to lead to higher > than normal levels of ripple on the output which could possibly cause some > inductive component somewhere to buzz or whine. > > I'm not sure if it is easy to measure the ripple on the output or if it is specified > anywhere how much ripple can be tolerated before logic errors start to > become a problem. > > Maybe it would be good to replace the capacitors in just the unit which is > whining to begin with and see if it makes a difference? I will try this by using the caps from other H744s that don't whine. > > To address the original question, I think I read somewhere that electrolytic > capacitors that are used for voltages a lot lower than their rating may fail to > maintain their dielectric formation which may in turn result in increased > leakage. > > Here's a thought. Could the whining be coming from an inductive filter > before the capactors because of excessive leakage through the capacitors > rather than because of high ESR? Would they benefit from re-forming? I did re-form the capacitors first. They didn't seem to need much as I ran them at 10V with zero leakage current (i.e. not measurable). Maybe I need to run the reforming process a bit longer anyway? > > Regards, > Peter Coghlan. > > > > >> > >> Christian > >
RE: Source for replacement caps in H744 regulators
> -Original Message- > From: Jonathan Chapman > Sent: 06 January 2022 13:00 > To: r...@jarratt.me.uk; Rob Jarratt ; General > Discussion: On-Topic and Off-Topic Posts > Subject: RE: Source for replacement caps in H744 regulators > > > One of the H744 regulators whines > > FWIW, none of mine are silent under load. If they're not being loaded (e.g. > on a test bench, with no dummy load, or if you have all the boards out) they > can whine excessively due to no minimum load. I was testing with a 1R resistor, so drawing 5A of the rated 25A. The other two H744s did not whine, but this one does. I can try a bigger load, I think the best I may be able to do is 10A, possibly 20A. > > > it seems higher than the expected values printed on the meter > > Beware cheap test equipment. $client has a few of these Chinese handheld > LC/RLC meters, they're wildly inaccurate on some parameters, including ESR > on large electrolytics. We've got a proper Gen-Rad RLC Digibridge in the shop > to compare against. We couldn't figure out why some of their tuned filter > stages were failing QC at a much higher rate than expected. They were off- > frequency because the cheap meters were giving consistently incorrect > measurements when trying to match capacitors. > My ESR meter is built from a design by Bob Parker. I got it from someone in Portugal (https://evbesrmeter.pt/), so I don't think it is a cheap Chinese one. > That said, it's not like replacing them with new will *hurt* -- it just might > not > fix the whine. > > Thanks, > Jonathan
RE: Source for replacement caps in H744 regulators
> >> -Original Message- >> From: cctalk On Behalf Of Christian Corti >> via cctalk >> Sent: 06 January 2022 10:02 >> To: General Discussion: On-Topic and Off-Topic Posts >> >> Subject: Re: Source for replacement caps in H744 regulators >> >> On Thu, 6 Jan 2022, r...@jarratt.me.uk wrote: >> > If I can't find 10V rated ones, then, generally up to what sort of >> > voltage rating can I go? Of course, physical size will be a factor, >> > but electrically can it affect operation of the regulator if the rated > voltage is >> too high? >> >> If you need to ask this, are you sure you want to do electronics repair? > > I am gradually learning. > I'm slowly picking this sort of stuff up as I go along too. I think that asking questions like this is the right thing to do when we are not sure about something and is not at all an indication that someone is somehow not suited to the task. Quite the reverse in fact. If we don't do this sort of work ourselves, it's not going to be easy to get someone else to do it and make sure it is done well for a reasonable price. Any contemporary electronics repair outfit, assuming one can be found, would probably recommend dumping the whole thing and replacing it with a "modern" power supply. > >> And what makes you think that you need to replace these caps at all? > I appreciate that there is lots of bogus advice out there which suggests that all capacitors need to be replaced before even starting to investigate the cause of problems but I think Rob has demonstrated that he is trying to figure out what is going on rather than just blindly replacing stuff. > > One of the H744 regulators whines and I have been told it could be the ESR > on these caps. I have measured the ESR on these particular ones (out of > circuit) and it seems higher than the expected values printed on the meter > and also the ESR is not stable, it fluctuates randomly. This suggests the > cap is not in great condition. > I guess from that the large capacitance of these units, they are probably filtering 50Hz or 100Hz ripple and high ESR is probably going to lead to higher than normal levels of ripple on the output which could possibly cause some inductive component somewhere to buzz or whine. I'm not sure if it is easy to measure the ripple on the output or if it is specified anywhere how much ripple can be tolerated before logic errors start to become a problem. Maybe it would be good to replace the capacitors in just the unit which is whining to begin with and see if it makes a difference? To address the original question, I think I read somewhere that electrolytic capacitors that are used for voltages a lot lower than their rating may fail to maintain their dielectric formation which may in turn result in increased leakage. Here's a thought. Could the whining be coming from an inductive filter before the capactors because of excessive leakage through the capacitors rather than because of high ESR? Would they benefit from re-forming? Regards, Peter Coghlan. > >> >> Christian >
RE: Source for replacement caps in H744 regulators
> One of the H744 regulators whines FWIW, none of mine are silent under load. If they're not being loaded (e.g. on a test bench, with no dummy load, or if you have all the boards out) they can whine excessively due to no minimum load. > it seems higher than the expected values printed on the meter Beware cheap test equipment. $client has a few of these Chinese handheld LC/RLC meters, they're wildly inaccurate on some parameters, including ESR on large electrolytics. We've got a proper Gen-Rad RLC Digibridge in the shop to compare against. We couldn't figure out why some of their tuned filter stages were failing QC at a much higher rate than expected. They were off-frequency because the cheap meters were giving consistently incorrect measurements when trying to match capacitors. That said, it's not like replacing them with new will *hurt* -- it just might not fix the whine. Thanks, Jonathan
RE: Source for replacement caps in H744 regulators
> -Original Message- > From: cctalk On Behalf Of Christian Corti > via cctalk > Sent: 06 January 2022 10:02 > To: General Discussion: On-Topic and Off-Topic Posts > > Subject: Re: Source for replacement caps in H744 regulators > > On Thu, 6 Jan 2022, r...@jarratt.me.uk wrote: > > If I can't find 10V rated ones, then, generally up to what sort of > > voltage rating can I go? Of course, physical size will be a factor, > > but electrically can it affect operation of the regulator if the rated voltage is > too high? > > If you need to ask this, are you sure you want to do electronics repair? I am gradually learning. > And what makes you think that you need to replace these caps at all? One of the H744 regulators whines and I have been told it could be the ESR on these caps. I have measured the ESR on these particular ones (out of circuit) and it seems higher than the expected values printed on the meter and also the ESR is not stable, it fluctuates randomly. This suggests the cap is not in great condition. > > Christian
RE: Source for replacement caps in H744 regulators
Rob, The voltage rating is just an absolute maximum. For PSU capacitors the other critical rating is ripple current. Lower voltages are The capacitance value won't be too critical either. At the time that was made typical electrolytic tolerances were -50/+100% So your 6,000uf could be anywhere between 3,000uf and 12,000uf when new, so I suspect these https://uk.rs-online.com/web/p/aluminium-capacitors/8556059 Sprague, 5,800uf 50v would be ok provided they physically fit... although RS has only one in stock... Dave > -Original Message- > From: cctalk On Behalf Of Rob Jarratt via > cctalk > Sent: 06 January 2022 08:53 > To: General Discussion: On-Topic and Off-Topic Posts > > Subject: Source for replacement caps in H744 regulators > > I think I may need to replace the two output capacitors in some of my H744 > regulators. These are screw terminal 6,000uF 10V parts. I have looked on > Mouser, Farnell and Digikey and there don't seem to be any available, and > any that are listed are really rather costly. > > > > Does anyone know where I might find some, preferably from a reputable > supplier. Note that I am in the UK. > > > > If I can't find 10V rated ones, then, generally up to what sort of voltage rating > can I go? Of course, physical size will be a factor, but electrically can it affect > operation of the regulator if the rated voltage is too high? > > > > Thanks > > > > Rob
Re: Source for replacement caps in H744 regulators
On Thu, 6 Jan 2022, r...@jarratt.me.uk wrote: If I can't find 10V rated ones, then, generally up to what sort of voltage rating can I go? Of course, physical size will be a factor, but electrically can it affect operation of the regulator if the rated voltage is too high? If you need to ask this, are you sure you want to do electronics repair? And what makes you think that you need to replace these caps at all? Christian
Re: Source for replacement caps in H744 regulators
On 06/01/2022 08:52, Rob Jarratt via cctalk wrote: > I think I may need to replace the two output capacitors in some of my H744 > regulators. These are screw terminal 6,000uF 10V parts. I have looked on > Mouser, Farnell and Digikey and there don't seem to be any available, and > any that are listed are really rather costly. I think I used Mouser part number80-PEH169HA460AQU2 to replace mine. I was also considering RS part number 381-9093 as an alternative though the voltage rating is quite a bit higher. Regards, Matt
