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| HP6268B Restoration |
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| AMR Labs:
I got a HP6268B off the e place and it was listed as untested. In the few published pictures it looked like it was in decent shape, and everything there that should be at least externally. I sent in a low offer and it was accepted, best of all shipping had been listed as free. Or was it... As you can guess that free shipping option was probably not a good idea after the seller found out what it would cost him to ship 80+ pounds. So he put it inside a flimsy cardboard box and a little cushioning on top and bottom of the box, but really very little on the sides. Needless to say it got damaged along the way. Probably some pissed off UPS worker that really was unable to handle the box must have dropped from at least from 3ft. Can't really blame this person, as the box which was barely larger than the power supply itself, no handles and poorly packed, was really unmanageable. During the fall the sharp edges of the front panel chewed its way out of the box so what I received was a big mess. Front panel bent at two corners, one handle bent slightly sideways , plus various dents, scratches and bent metal at several other areas. The rear junction block where the remote programming and sensing wires connect is bent upwards, but luckily nothing broken nor has the PC board suffered any damage. Fortunately the meters where still intact, and the front knobs and more importantly the controls seemed to be ok. Two of the knobs seem to have lost its cap but that was the way it was shown in the listing, but the two other knobs survived. There was also some sort of rattling like loose parts towards the rear when the equipment was turned over, but I could not see anything moving around or make it fall out. This turned out to be inside the red RFI assembly box, where 3 out of 4 spacers where broken off and there where some loose screws as well, along with various washers. So far found everything except for the last screw that holds that cover in place. Out of the 4 screws that hold that cover 2 where missing. Its like some hamfisted dolt forced his way in there and in the process broke several threads made of soft aluminum, just to then hastily threw everything back together. This could not have happened due to the recent tumbles in shipment. I noticed that one of the broken off spacers is what actually completes the connection between one of the inbound AC sides and the Triac that is part of the preregulator, so this power supply could have never worked this way, I wonder if this might have been be the problem and the reason it was listed as "untested". I checked the Triac and it is ok. On the board inside the preregulator red box there are 3 RIFA caps which looked very crazed, one even having a gash on the side. First thing was to re-strap the power supply for 115V for testing, as I don't have 230V at my bench. this involved reconfiguring both transformers T1 the (huge!) main and T2 the bias transformers. Also two jumpers need to be added and one removed, plus a 390 ohm 2W resistor needs to be added as well on the RFI assembly board. Then tested the power supply by substituting the triac with a light bulb to prevent any big surges or possibly any shorts from causing fireworks, and it basically came up and regulation seemed was working fine as I was able to vary the voltage from zero to almost up to 40V. I was thrown off for a while and stuck at zero output because had not noticed that both current controls where set to minimum, which basically prevents the supply to provide any output voltage at all. So this fixed that, but then the overvoltage started triggering, and again by just setting the front panel adjustment to fully CW solved that. I was even able to connect a 12V car bulb that draws 0.5Amp and it was holding fine, but anything above 1amp caused the voltage to slowly fall back. Given that the whole preregulator is out of the loop, and the light bulb in place of the triac was only allowing about 75V AC to reach the transformers, that should be normal for now. So needed to order the replacement for the 3 RIFAS, and also all the electrolytic caps on the A1 main board. One of the bigger caps (orange one) on that board clearly has outgassed on one side, but no signs of corrosion. There are in total perhaps under a dozen caps on the board total that will be replaced. They all look to be from the 80s given their size to value ratio. Some nudie pictures attached. |
| AMR Labs:
Some preregulator pictures inside the RFI assembly A2 board, as found with rattles inside. Crazy crazed Rifas and broken off spacer threads. |
| wn1fju:
It's amazing just how much damage can be done by mechanical shock. I received a piece where the transformer broke free and tumbled around the unit ripping away some components that happened to stick up out of the board. I've gotten pieces where large electrolytic capacitors have ripped out of the board. Relays in a socket without a hold-down strap? No way they stay put. I even had one piece, which consisted of a shallow rectangular box with about four large PC boards mounted on standoffs, where every single board had ripped off their standoffs. Now I can't know for sure whether any of these faults existed before the seller put the thing in the shipping box, but I kind of doubt it. Not to mention the FedEx driver who rather than walk the extra 10 feet to my front porch, is fond of placing small packages right in back of my car (where I don't usually look) maybe in the hopes that I will back out and run the packages over! |
| AMR Labs:
Crazed RIFA caps have been replaced in the RFI assembly preregulator, and 115V conversion steps had all been completed. Also replaced all the electrolytics on the A1 main board. In the rush to order parts forgot to include the 390 ohm 2W resistor that is part of the 115V conversion, but was able to put together a temp replacement combination with what I had. Otherwise all went together as planned. Had to disconnect the power to the bigger fan attached to the heatsink assembly, the constant noise was driving me crazy. I will implement a switch probably on the back panel to turn it on only when really needed under high power long term requirements. On normal short term or lighter loads the power supply stays cool as a cucumber. Its absolute madness to have those fans running at full speed all the time for hobby lab use. I am thinking of doing it for both fans on one switch. The smaller fan actually just sucks air into the cabinet towards the general direction of the main transformer which is some distance away anyhow, and runs constantly as well. Not needed most of the time I expect, and it will save some dust accumulation and my nerves. Worst comes to worst I can reverse the flow of the smaller fan to extract air and leave it running as it is much less annoying. Also pulled out the whole panel to try and straighten out the bent corners and give it a good clean, and set the voltmeter pointer that needed a tiny tweak back to exact zero and the adjustment screw is hidden behind the panel anyhow. Given I don't have access to a 10 ton hydraulic press I think the corners look quite acceptable for now. Found another something rattling around somewhere under the heatsink assembly so had to remove it. It was a royal pain in the posterior the get this to come out as there are clearance issues on almost all sides. Manual says to just remove two screws that hold it to the chassis on one end, slide forward to disengage two additional holding pins and then bring out by "sliding heatsink down about 1/2" and slightly away from chassis". Come again, say what? I spent almost an hour but various things would still hit the chassis or other areas, and the fan on the end of the assembly was already at its end of travel as it was bumping into the output terminals just in front of it, while the other end where the two screws where removed was still half way under the edge of the chassis. In the end decided to just remove the rear panel by taking off 3 screws on each side and then things started to happen much easier. I think HP forgot to mention this step in the instructions, or the Marquis de Sade got involved. So worth noting if you ever encounter yourself trying to pull out one of these heatsink assemblies. In the end the rattling was yet one more loose screw from the RFI assembly red box. So was doing some load testing with my HP6060B electronic load. Everything checked out nicely, the power supply is super stable, practically no drift that I can detect on a 4.5 digit DMM once you set the output voltage. Both analog meters are dead on accurate, that is as accurate as a needle on a scale can be. Tested the supply under various loads, starting with 5amps, then went to 10, 20, 25, and finally 30 amps. Absolutely rock solid. The voltage actually raises a bit under heavy load by about 50-80mV. For example if I set it to 12.00 volts and apply a load of 25amps, the voltage raises to 12.08V or thereabouts (DMM always right at the output terminals). About the same as well on 10-20 amps loading. I did not see any adjustment in the service manual calibration section that might be able to compensate for this, but I guess it might be normal within spec? Will have to check the load regulation specifications. That's it for now. |
| factory:
In case you missed it, for 115V operation the mains circuit breaker is replaced with 30A one, 230V operation has a 20A one. And two of the original capacitors were type 150D, these are wet tantalum types. Re the voltage error, have you got the sense connections wired up? David |
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