HP 35665A Dynamic Signal Analyzer memory upgrade hack... - Page 1
Forum section: electronics / testgear

author: Sören_Marodören
author_rank: Contributor
timestamp: October 18, 2019, 03:28:25 pm
content: Hi,I have just recently got an HP 35665A Dynamic Signal Analyzer.For the moment there is only one option in it, ID2 - Swept Sine Measurements.I will soon upgrade it from here:https://www.glkinst.com/test-equipment/But when I opened the unit to replace the battery, I noticed that there are already extra RAM mounted on my Memory Board.There are 8 x M5M44256BL (4x256kByte) in the area called "STANDARD RAM" and another 8 x M5M44256BL in the area called "OPTIONAL RAM".I suppose this means that I have 2MByte of RAM. Why is it called OPTIONAL RAM?On another place of the board there is a jumper called "RAM" and that is marked "1M". Anyone who know what that is for?So, now to the question:Is it possible to replace these RAM circuits and upgrade it to a 4 or 8MByte board?Pictures of the memory upgrade boards looks very similar to my board.The only difference I have noticed is the 1M-jumper that is removed on at least the 4MByte board.(But there might be differences hidden in the Flash memories that looks the behavior...)And by the way: Anyone who have schematics available for this instrument? I need to do some flout finding on the signal generator.I have two spuriouses at 24.666 kHz and 34.588 kHz. Might be some bad decoupling or filtering somewhere.Thanks in advance,/Sören

author: Tomorokoshi
author_rank: Super Contributor
timestamp: October 18, 2019, 04:12:29 pm
content: I did the GLK upgrade. My unit already had 8 MB. Because you found the GLK kit, I expect you also found the 35665-90060 memory upgrade procedure document he references.Many have looked for schematics for the 35665. I'm not sure any are out there.When it comes to DRAM parts of that era it was very common to have a couple banks that would be populated with one type of part or the other, consisting of 256k, 1M, or 4M parts. Jumpers then select the configuration. The 8MB upgrade would involve de-soldering the 256k parts and replacing them with 4M parts.Sorry; spelling mistake in model numbers of images. Should be 35665.

author: Sören_Marodören
author_rank: Contributor
timestamp: October 18, 2019, 04:39:58 pm
content: Thanks Tomorokoshi,I will try to replace the 2x8 x M5M44256 (4x256k) that I have with 8 x M5M44400 (4x1M).I also notice that on your board the jumper (R101) is removed. Probably that has something to do with selecting the optional area (that is not populated on your board).When I have you on the line: Do you also see two spurrs in the Source signal at 24.666 kHz and 34.588 kHz? They are at -95..-100dBV.If they are very common it is probably not worth spending time to remove them.Cheers,/Sören

author: Tomorokoshi
author_rank: Super Contributor
timestamp: October 18, 2019, 04:55:17 pm
content: No, mine is quiet. In your scan there aren't spurs at either the sum or difference frequencies of 10 kHz and 59 kHz. Not sure what it's coming from, although suspects could include the switching power supply or the CRT.Here is mine out in the open with no shielding when I was adjusting the CRT yoke.Do you see the same spurious signals on Channel 2?

author: Cubdriver
author_rank: Unknown
timestamp: October 18, 2019, 07:57:14 pm
content: I'd be interested to know if there is any repair documentation available for this beast, too - I have a dead one purchased a few years ago waiting patiently in my lengthy repair queue.-Par

author: Sören_Marodören
author_rank: Contributor
timestamp: October 18, 2019, 08:21:35 pm
content: I see no spurs if I don't have Source connected. Both Ch1 and Ch2 looks nice and clean when unconnected or terminated.The spurs are very stable in frequency. So they seem to come from a clock or something else running at a fixed frequency.And it does not matter if I have the Source on or off or what frequency I set it to.If I look closer I see that the one at 24.666 kHz actually is a small forest with spurs separated by 55 Hz. See picture.So something is modulating it.The spurious at 34.588 kHz is nice and clean and only made of one frequency.What about 10 kHz and 59 kHz? Are they some internal frequencies?

author: Sören_Marodören
author_rank: Contributor
timestamp: October 19, 2019, 11:10:21 am
content: Tomorokoshi, I don't get the numbers right.If I have 16 x 4x256k that is in total 8 x 256kByte or 2MByte.But you have 8 x 4x1M that should be 4 x 1MByte or 4MByte.Are you sure you have 8MByte in your machine?What does it say on the screen during startup? (On mine it says "Main RAM 2097152 0x00e00000")When I look closer on the datasheets for the memories, the only difference is that pin 5 was not used on M5M44256BL but is used as A9 on the M5M44400BL. And one extra pin used for both row and column addressing gives 4 times the memory size.Cheers,/Sören

author: Tomorokoshi
author_rank: Super Contributor
timestamp: October 19, 2019, 02:29:42 pm
content: You are correct. Mine has only 2MB.

author: Sören_Marodören
author_rank: Contributor
timestamp: October 19, 2019, 03:57:09 pm
content: But you should have 4MByte of RAM. Right?Otherwise there is something that I don't understand.

author: picburner
author_rank: Frequent Contributor
timestamp: October 19, 2019, 07:09:35 pm
content: I tried to find the service manual but unfortunately I didn't find anything.However, while I was doing the research, I found this file which I hope will be useful:

author: Tomorokoshi
author_rank: Super Contributor
timestamp: April 16, 2022, 12:10:24 am
content: Quote from: Sören_Marodören on October 19, 2019, 03:57:09 pmYou are correct, I misunderstood the memory amount. The memory test screen shows 2290624 bytes available, so I expect the rest of the system is using around 1.8 MB.