Well after turning on my HP3314A after a few months of non use I noticed my screen was blank too. Following your video I had an issue also with the -15 volt rail. It too is the same capacitor problem… thanks Gary for these really useful instructive repair vids much appreaciated.
Repairing equipment is a lot like solving a crime. Except it is a lot messy! My dishwasher was giving problems recently and after a lengthy faultfinding, I realised that the hose connecting the pressure sensor was leaking because of a bad hose-clamp. No sensors... not the relay on the control board which I replaced... nothing sinister in the software... a plain old cheap hose-clamp! Great repair video, thanks Gary! Let's hope no.3 will be the last one for this instrument! Good luck!
You might want to look into those MOSTEK ROMs on the main board. These are known to fail over time getting corrupt bits. If any ROM has incorrect contents the processor will most likely crash and go into an endless loop. This unit appears to have a 6800 family microprocessor and these typically go into an endless loop cycling through the whole address space reading each memory location sequentially. Probing the address lines with a scope can check this with each address line having a square wave on it halving in frequency for each successive address line from A0 through to A15.
@@stephenbell9257 It looks like it is doing exactly as you describe. The address lines are all toggling like they should, but the all 8 data lines have some invalid logic levels (+2 V) at times. I doubt that the 6800 is bad; and I’m hoping it’s not the ROMs. Could be anything on that data bus causing this problem. I don’t have a logic analyzer, or a signature analyzer either (they never did work the way they were intended anyway.) But, right now, I have bigger issues: recovering from Hurricane Beryl, which came right through my area. It will take me a little while before I can get back to work on this unit.
@@garyramsey4275 Some invalid logic levels are normal during times when the data bus isn't being driven by a device. You can better check the logic levels by triggering your scope off the chip select line of a device and verifying that the logic levels are OK towards the end of the chip select pulse. Repeat this for each memory and peripheral device on the microprocessor bus to verify that all devices are driving correct logic levels onto the data lines. It is highly likely that you have a bad ROM as these MOSTEK ROMs are notorious for failing like this - it is so common that the term "ROM rot" has been coined to describe it. There is a procedure for checking the ROMs on power up. K6JCA has a detailed repair log for this exact problem so it would be worth checking this log. It refers to replacement ROM images being available on the KO4BB web site but this appears to be non-functional at the moment. However, there may be other sources out there for getting these ROM images since this seems to be a relatively common problem. I hope you have success in bringing this instrument back to life!
Hi Gary was wondering if ud be able to help I changed both the capacitors.. still no screen and checking the voltages I not seeing -15 at all. So again I discounnected that board and was still showing low voltage on -15 rail. Would u hv any pointers?
@@MrAppleimac01 I simply did a google search, and as I recall, I believe I actually found it at Walmart.com . Quite expensive, but it was the exact replacement. I purchased 2 of them, so I would have a spare, but one of them arrived with one of the spot welded wires broken off. I still have that spare, but I think it’s unusable.
One other thing if i may… I watched how you changed the plastic back to white. What do you use to clean the front panel without taking off any of the silk screen.
@@MrAppleimac01 well, the peroxide I used to bleach the plastic actually damaged the paint on the metal part of the front panel, removing much of the paint completely down to bare metal! The panel you see on the finished unit is a replacement from another unit. Sometimes I use a spray household cleaner (Formula 409, or similar) to clean front panels, but sometimes this can be too harsh. I usually will start with plain water on a paper towel, and work my way up to stronger cleaners, maybe spray the 409 onto the paper towel first. That usually works fine. For really dirty surfaces I’ll spray directly onto the surface, but only if gentler methods don’t work. I also like to use cheap disposable paintbrushes, with the bristles trimmed short to about 2cm, to scrub really dirty surfaces. I keep 2 of these; one for water and water-soluble detergents, and another for alcohol or other solvents. For stubborn stains, paint, adhesives, etc I will use isopropyl alcohol, a few drops on one of those paintbrushes and some careful scrubbing will usually get it looking like new.
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Well after turning on my HP3314A after a few months of non use I noticed my screen was blank too. Following your video I had an issue also with the -15 volt rail. It too is the same capacitor problem… thanks Gary for these really useful instructive repair vids much appreaciated.
Repairing equipment is a lot like solving a crime. Except it is a lot messy!
My dishwasher was giving problems recently and after a lengthy faultfinding, I realised that the hose connecting the pressure sensor was leaking because of a bad hose-clamp. No sensors... not the relay on the control board which I replaced... nothing sinister in the software... a plain old cheap hose-clamp!
Great repair video, thanks Gary! Let's hope no.3 will be the last one for this instrument! Good luck!
At 5:20, you should be saying to yourself, “That’s when he realized, he F’ed up.”
You might want to look into those MOSTEK ROMs on the main board. These are known to fail over time getting corrupt bits. If any ROM has incorrect contents the processor will most likely crash and go into an endless loop.
This unit appears to have a 6800 family microprocessor and these typically go into an endless loop cycling through the whole address space reading each memory location sequentially. Probing the address lines with a scope can check this with each address line having a square wave on it halving in frequency for each successive address line from A0 through to A15.
@@stephenbell9257 It looks like it is doing exactly as you describe. The address lines are all toggling like they should, but the all 8 data lines have some invalid logic levels (+2 V) at times. I doubt that the 6800 is bad; and I’m hoping it’s not the ROMs. Could be anything on that data bus causing this problem. I don’t have a logic analyzer, or a signature analyzer either (they never did work the way they were intended anyway.) But, right now, I have bigger issues: recovering from Hurricane Beryl, which came right through my area. It will take me a little while before I can get back to work on this unit.
@@garyramsey4275 Some invalid logic levels are normal during times when the data bus isn't being driven by a device. You can better check the logic levels by triggering your scope off the chip select line of a device and verifying that the logic levels are OK towards the end of the chip select pulse. Repeat this for each memory and peripheral device on the microprocessor bus to verify that all devices are driving correct logic levels onto the data lines.
It is highly likely that you have a bad ROM as these MOSTEK ROMs are notorious for failing like this - it is so common that the term "ROM rot" has been coined to describe it. There is a procedure for checking the ROMs on power up. K6JCA has a detailed repair log for this exact problem so it would be worth checking this log. It refers to replacement ROM images being available on the KO4BB web site but this appears to be non-functional at the moment. However, there may be other sources out there for getting these ROM images since this seems to be a relatively common problem.
I hope you have success in bringing this instrument back to life!
Hi Gary was wondering if ud be able to help I changed both the capacitors.. still no screen and checking the voltages I not seeing -15 at all. So again I discounnected that board and was still showing low voltage on -15 rail. Would u hv any pointers?
@@MrAppleimac01 it’s a linear power supply; standard troubleshooting techniques should work.
Im going through mine following you very informative videos thanks. Can I ask where got the replacement battery
@@MrAppleimac01 I simply did a google search, and as I recall, I believe I actually found it at Walmart.com . Quite expensive, but it was the exact replacement. I purchased 2 of them, so I would have a spare, but one of them arrived with one of the spot welded wires broken off. I still have that spare, but I think it’s unusable.
One other thing if i may… I watched how you changed the plastic back to white. What do you use to clean the front panel without taking off any of the silk screen.
@@MrAppleimac01 well, the peroxide I used to bleach the plastic actually damaged the paint on the metal part of the front panel, removing much of the paint completely down to bare metal! The panel you see on the finished unit is a replacement from another unit. Sometimes I use a spray household cleaner (Formula 409, or similar) to clean front panels, but sometimes this can be too harsh. I usually will start with plain water on a paper towel, and work my way up to stronger cleaners, maybe spray the 409 onto the paper towel first. That usually works fine. For really dirty surfaces I’ll spray directly onto the surface, but only if gentler methods don’t work. I also like to use cheap disposable paintbrushes, with the bristles trimmed short to about 2cm, to scrub really dirty surfaces. I keep 2 of these; one for water and water-soluble detergents, and another for alcohol or other solvents. For stubborn stains, paint, adhesives, etc I will use isopropyl alcohol, a few drops on one of those paintbrushes and some careful scrubbing will usually get it looking like new.