7854 - yet another problem
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The 7854 I'm trying to resurrect has a problem where the readout starts to
flicker a lot after it has been on for a short while. If I them power off and power on I see all vertical mode lights on and CHOP and B lit in the horizontal mode lights. This I understand is a "Real time clock" failure. So where do I find the darn RTC so I can try to fix it - a quick scan of the friendly service manual didn't lead me to it ... Thanks Dave
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Harvey White
On Sun, 3 Feb 2019 19:00:50 -0000, you wrote:
The 7854 I'm trying to resurrect has a problem where the readout starts to If this is like some of the others, the CPU doesn't have an RTC module, too old for that. I'd look for the battery, but I suspect you may have a dallas RAM/ROM buried in there, some of them have/had RTC modules. Harvey
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The 7854 I'm trying to resurrect has a problem where the readout starts to
flicker a lot after it has been on for a short while. Hi David, if you store a waveform, is it flickering as well? I had a similar problem with the -15V supply on my 7854. It showed OK DC values by got ripple after a short time running. It was a 330uF filter cap in the powersupply. -- Best regards, Fred S.
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The problem was simple once it got bad enough that I could hear the crackle/hiss of EHT leakage - I removed the CRT (easier said than done), thoroughly cleaned the cable and around the seal where it connected to the PDA mesh (even though there was little if any sign of carbon tracking), and put it back together. Since then (so far) it has behaved perfectly .
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PS I think the "real time clock" problem may have been related as it hasn't recurred. I think the real time clock refers to a problem with the "50Hz" signal from the Readout Acquire circuit (schematic <31>). Strangely the actual frequency in this scope was close to 70Hz (even though the timing R & C connected to pin 6 of U2510 were pretty much spot on value). Strangely U2510 isn't shown in the parts list for the Display Board (A29). It's a 155-0021-01 timing generator and swapping it with one from another readout board made no change. David
-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of fred@... Sent: 05 February 2019 15:21 To: TekScopes@groups.io Subject: Re: [TekScopes] 7854 - yet another problem The 7854 I'm trying to resurrect has a problem where the readout starts to flicker a lot after it has been on for a short while. Hi David, if you store a waveform, is it flickering as well? I had a similar problem with the -15V supply on my 7854. It showed OK DC values by got ripple after a short time running. It was a 330uF filter cap in the powersupply. -- Best regards, Fred S.
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Chuck Harris
The 7854 is based on a ti-9900 16 bit minicomputer emulating
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microcomputer. Bank in the vernacular of the time, a "real time clock" was a counter driven off of the power line. I can't think of a reason for a 7854 to have such a clock, but I haven't studied it extensively. -Chuck Harris David C. Partridge wrote:
The problem was simple once it got bad enough that I could hear the crackle/hiss of EHT leakage - I removed the CRT (easier said than done), thoroughly cleaned the cable and around the seal where it connected to the PDA mesh (even though there was little if any sign of carbon tracking), and put it back together. Since then (so far) it has behaved perfectly .
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n4buq
Same chip used in the TI-99/4A?
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Thanks, Barry - N4BUQ
The 7854 is based on a ti-9900 16 bit minicomputer emulating
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Chuck Harris
Same family, but likely physically bigger.
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-Chuck Harris n4buq wrote:
Same chip used in the TI-99/4A?
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Harvey White
On Tue, 5 Feb 2019 16:52:07 -0500, you wrote:
Same family, but likely physically bigger.64 pin DIL package, I think. Wonder what would happen if you somehow managed to recode everything for an ARM processor? Harvey
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Chuck Harris
Nirvana.
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I have an adapter CPU card for just such a venture. A guy named John Seamons, of timenuts fame, designed an interface board between a Beagle Bone Black/Green single board computer and the HP5370A/B frequency counter. A BBB/G SBC plugs directly into his board, and the interface board plugs directly into the CPU's slot in the 5370A/B motherboard. The BBB/G SBC runs the original 6802 firmware using a linux hosted 6802 emulator. The BBB/G SBC also runs a SSH server that allows you to communicate directly with the 5370 counter, does enhanced software processing of the counter's data (Allen Variance, printing, plotting..., and provides both ethernet and USB interconnectivity. Faster, lower power, more features... Nirvana. -Chuck Harris Harvey White wrote:
On Tue, 5 Feb 2019 16:52:07 -0500, you wrote:Same family, but likely physically bigger.64 pin DIL package, I think.
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Harvey White
On Wed, 6 Feb 2019 08:10:38 -0500, you wrote:
Nirvana.Let you know when I get the DM5110 done like that. Front panel readouts work, sooner or later switching and instrument interface. ST micro F446 processor on their Nucleo 64 board, FPGA for front panel, and one of two 488 bus chips on an add-on board. I *could* write an emulator that would run the original code from the ROM dump, but the possibility of programming in C (rather than 6802 assembly), adding an OLED readout behind the front bezel, and adding more functions (such as a built in cal routine), well.... no assembly... Another option would be to take the CPU board, add a readout, use a 488 controller, add a wifi module running MQTT, and then having a bit of fun with that. Separate case, of course. Harvey
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