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7704A heatsink 54C/130F too hot?

John W0MPM All Messages By This Member #172848 A free 7704A showed up here and seems to work 'OK'. I noticed the heatsink was REALLY hot to touch. The measured temperature is 130F / 54C. Is this in the normal range? (Yes this is a cross-post from the other group.) Voltages check normal. I'm reading all the past posts and getting ready to address the trace dimming after about 5 minutes (still usable) and uneven trace (dim left to bright right), especially at faster sweep rates. W0MPM John
Chuck Harris #172850 Does the fan work? -Chuck Harris John Brown via groups.io wrote: toggle quoted message Show quoted text A free 7704A showed up here and seems to work 'OK'. I noticed the heatsink was REALLY hot to touch. The measured temperature is 130F / 54C. Is this in the normal range? (Yes this is a cross-post from the other group.) Voltages check normal. I'm reading all the past posts and getting ready to address the trace dimming after about 5 minutes (still usable) and uneven trace (dim left to bright right), especially at faster sweep rates. W0MPM John
John W0MPM All Messages By This Member #172851 Don't see a fan on the 7704a. Searching in the manual can't find any reference or illustration showing a fan. And the temperature is even behind each of the pass transistors so it does not appear any one element is generating a bunch more heat than the others. Maybe this is normal? But as Maui said 'Hot hot hot'. (You have to be conversant with Disney princesses to understand. My assistant is 4 1/2.) -- W0MPM John
Colin Herbert All Messages By This Member #172852 I don't think that the 7704 or 7704A have a fan. They both have SMPS power-supplies, don't they? Take a look at the back of either and you can see a sizeable heat-sink with several fins, but no vent-hole, with or without a filter, that might indicate the presence of a fan. TekWiki is your friend. Colin. toggle quoted message Show quoted text -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John Brown via groups.io Sent: 03 November 2020 17:04 To: [email protected] Subject: Re: [TekScopes] 7704A heatsink 54C/130F too hot? Don't see a fan on the 7704a. Searching in the manual can't find any reference or illustration showing a fan. And the temperature is even behind each of the pass transistors so it does not appear any one element is generating a bunch more heat than the others. Maybe this is normal? But as Maui said 'Hot hot hot'. (You have to be conversant with Disney princesses to understand. My assistant is 4 1/2.) -- W0MPM John
Chuck Harris #172853 Looking through the manual, I see that the 7704A, like the 7904, has no fan. The 7904A, on the other hand has a fan, hence my question about fans... Power transistors and rectifiers laugh at 130F heat. Many are rated for operation up to 200C. The real concern for the engineers is will someone, or something, get burned by this exposed heat sink? And, the answer is no, as long as the temperature stays below about 180F (80C), you would touch it, and move away long before getting burned. -Chuck Harris Chuck Harris wrote: toggle quoted message Show quoted text Does the fan work? -Chuck Harris John Brown via groups.io wrote: A free 7704A showed up here and seems to work 'OK'. I noticed the heatsink was REALLY hot to touch. The measured temperature is 130F / 54C. Is this in the normal range? (Yes this is a cross-post from the other group.) Voltages check normal. I'm reading all the past posts and getting ready to address the trace dimming after about 5 minutes (still usable) and uneven trace (dim left to bright right), especially at faster sweep rates. W0MPM John
Dave Seiter All Messages By This Member #172858 Some 7704As have fans (I assume the newest ones), I have one. -Dave toggle quoted message Show quoted text On Tuesday, November 3, 2020, 09:26:33 AM PST, Colin Herbert via groups.io <colingherbert@...> wrote: I don't think that the 7704 or 7704A have a fan. They both have SMPS power-supplies, don't they? Take a look at the back of either and you can see a sizeable heat-sink with several fins, but no vent-hole, with or without a filter, that might indicate the presence of a fan. TekWiki is your friend. Colin. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John Brown via groups.io Sent: 03 November 2020 17:04 To: [email protected] Subject: Re: [TekScopes] 7704A heatsink 54C/130F too hot? Don't see a fan on the 7704a. Searching in the manual can't find any reference or illustration showing a fan. And the temperature is even behind each of the pass transistors so it does not appear any one element is generating a bunch more heat than the others. Maybe this is normal? But as Maui said 'Hot hot hot'. (You have to be conversant with Disney princesses to understand. My assistant is 4 1/2.) -- W0MPM John
k6whp All Messages By This Member #188322 ,as does mine. But, on that subject, I wonder if anyone who DOES have a 7704A with a fan has the one that is mounted laterally to the upper chassis above the horizontal bays and can explain the nature of the rather complex PCB with one IC and a number of discreet components. The fan seems to blow air OUT of the case in the vicinity of the CRT rear end. It is powered by a two-wire lead from the illuminated graticule pot. Why the elaborate circuitry and why the fan mounted on the board with a semi-circular array of solder points. Apologize for the crappy description. I have a 7704A service manual but it contains no mention of the board/fan setup. Appreciate an explanation. -- William, k6whp "A friend told me to cheer up, things could be worse. So I cheered up and, sure enough, things got worse!"
Albert Otten All Messages By This Member #188324 board with a semi-circular array of solder points Probably the old style "Siemens" fan motor 147-0035-00. At present there is one at Ebay. Board for instance pictured in (my) 7104 manual, Fig. 8-22, <14>, page 328. Albert
k6whp All Messages By This Member #188328 On Thu, Nov 25, 2021 at 01:06 AM, Albert Otten wrote: Thanks. Saw the eBay listing. My motor and fan work fine. Was looking for explanation/documentation of the whole board and why such a seemingly simple concept of a cooling fan had all the added circuitry. I have a printed manual, a copy of the BAMA manual, and the Artek manual and none of those contain a schematic or description of the fan board. Not essential; just curious. 147-0035-00 -- William, k6whp "A friend told me to cheer up, things could be worse. So I cheered up and, sure enough, things got worse!"
Albert Otten All Messages By This Member #188330 Was looking for explanation/documentation of the whole board and why such a seemingly simple concept of a cooling fan had all the added circuitry. Hi William, A circuit diagram is shown in the 7904A manual (Tekwiki, 3rd manual) at page 333. Short Theory at page 109. I hope this helps you a little further. Albert
Sigur?ur ?sgeirsson All Messages By This Member #188333 ?ann fim., 25. nóv. 2021 kl. 15:15 skrifa?i k6whp <k6whp@...>: On Thu, Nov 25, 2021 at 01:06 AM, Albert Otten wrote: Thanks. Saw the eBay listing. My motor and fan work fine. Was looking for explanation/documentation of the whole board and why such a seemingly simple concept of a cooling fan had all the added circuitry. While I’ve never seen a 7704A, my guess would be that the circuitry is the same as in the 485, 2465 and other scopes that use the Siemens motor. The circuitry does two things; commutates the brushless motor on signals from the Hall effect sensors in the motor, and temperature-regulates the fan speed. The impeller fan design in the 2465 is IMHO vastly better than the PC fan used in my 2467. The former is virtually silent, while the latter is annoyingly loud and whiny. I imagine by that time, it would have made for a fair cost saving to design in a by-then commodity PC fan, which is presumably why Tek went backwards in this respect.

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