TheseGoToEleven
Active member
- Joined
- Sep 4, 2020
- Messages
- 43
Let’s open up this Melcor 1731 op amp and see what makes it tick.
The plastic case has no shielding inside. Its contents are all suspended in a sort of semi-clear, rubbery gel. It reminds me of the fruit and jello molds that used to be so popular, except this was made by engineers and is probably far less tasty.
Here is what it looked like after removing most of the clear goop. It’s a little easier to see what we’re looking at now.
The circuit board only has traces on the bottom. All of the components have been installed through-hole style. Some capacitors have long leads covered with wire insulation. There is also an orange wire connecting two separate areas, jumping over the traces in between. There are a couple of unused through holes and traces. Perhaps these were used in older 1731s.
Here are two of the previous shots with component and net names added.
I have attached the resulting schematic to match, which also includes a bill of materials. I measured most of the components but since this was an old and non-working / noisy unit, their characteristics have likely drifted from spec. The carbon comp resistors, for example, all seem to have increased in ohms.
Enjoy, and many thanks to Whoops for providing the 1731! I don’t know the age of this unit, so if anyone can help with dating it, please chime in. The BOM lists some additional markings on the transistors, which I think are date codes, but I'm not 100% certain how to interpret them.
The plastic case has no shielding inside. Its contents are all suspended in a sort of semi-clear, rubbery gel. It reminds me of the fruit and jello molds that used to be so popular, except this was made by engineers and is probably far less tasty.
Here is what it looked like after removing most of the clear goop. It’s a little easier to see what we’re looking at now.
The circuit board only has traces on the bottom. All of the components have been installed through-hole style. Some capacitors have long leads covered with wire insulation. There is also an orange wire connecting two separate areas, jumping over the traces in between. There are a couple of unused through holes and traces. Perhaps these were used in older 1731s.
Here are two of the previous shots with component and net names added.
I have attached the resulting schematic to match, which also includes a bill of materials. I measured most of the components but since this was an old and non-working / noisy unit, their characteristics have likely drifted from spec. The carbon comp resistors, for example, all seem to have increased in ohms.
Enjoy, and many thanks to Whoops for providing the 1731! I don’t know the age of this unit, so if anyone can help with dating it, please chime in. The BOM lists some additional markings on the transistors, which I think are date codes, but I'm not 100% certain how to interpret them.