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+--- Thread: 32K SRAM board (MB1732) troubleshooting (/thread-509.html)
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RE: 32K SRAM board (MB1732) troubleshooting - Ernest - 09-06-2022
Hi Witchy,
The load speed can be a factor, try using 300 bps if you can and see how that goes, the lower speed is a little less prone to tape speed variations that is seen on old tape players. I find the most reliable is using a modern computer and output the wave file from the sound card. However these days I rarely input from tape.
There has been a number of engineering changes to the Cassette interface over time to improve reliability, some of these if done post manufacture may have resulted in just lifting a leg rather than full removal (easier to reinstate later if needed, check out the engineering notes in the handbook
Maybe Ewan or someone can answer the "How did Microbee test the main boards before adding the RAM?" question as they had closer association with the production back in the day, I came along much latter.
However, many systems like these were tested using purpose built test jigs, if you have a look at the engineering technical manual there is a template for making some angle brackets to have the Coreboard at 90 degrees to the mainboard for repairs and troubleshooting. I have a set of these and is very very useful.
There are also a couple of TEST EPROMs in the repository which can be helpful in testing the the Microbee. Having multiple systems is also very useful when repairing especially if you have a known fully working system to swap between.
Ernest
RE: 32K SRAM board (MB1732) troubleshooting - MbeeTech - 10-06-2022
(09-06-2022, 11:27 AM)Ernest Wrote: Maybe Ewan or someone can answer the "How did Microbee test the main boards before adding the RAM?" question
To my knowledge, the standard & premium baseboards were fully populated then tested with known working coreboards.
If they failed / didn't start, then they would be looked at by a technician in the production area.
The 256TC model was the first to have a bed of nails test jig made for some basic functional testing.
Microbee didn't have any Automated test equipment (that I know of) and relied on getting manufacturing procedures
right to decrease failure rates off the production line.
RE: 32K SRAM board (MB1732) troubleshooting - someone - 11-06-2022
Loading from tape from an Apple ][, a microbee or other home computer that uses a 3rd party tape deck has always been unreliable at best.
Even the well known quality brands such as National(Panasonic) & Sony can be problematic.
This is because tape decks are designed to play music and as such contain audio features like ALC (Automatic Level Control), EQualisation, Dolby Noise Reduction, bias adjustments and tone controls that distort the signal. Other issues include azimuth adjustment, tape speed variation, mic & output impedance. If the azimuth is not correctly adjusted unwanted crosstalk can occur. Sanyo is notorious for speeding up.
What's required is a tape deck that faithfully records & reproduces 1200 and 2400 Hz tones - Nothing more & nothing less.
The D1122 Micron Computer Program Data Recorder from Altronics proved to be quite reliable although their automatic rewind button release didn't always work.
Modern audio WAV players work reliably.
RE: 32K SRAM board (MB1732) troubleshooting - Witchy - 13-06-2022
(10-06-2022, 09:50 AM)ejwords Wrote: To my knowledge, the standard & premium baseboards were fully populated then tested with known working coreboards.
If they failed / didn't start, then they would be looked at by a technician in the production area.
Ah right. I was thinking of just making a couple of riser boards so I could at least have the RAM board a few inches above the main board to be able to get probes etc in. Easy done with a couple of protoboards and some SIP headers etc.
Cheers
Witchy
(11-06-2022, 04:00 PM)someone Wrote: What's required is a tape deck that faithfully records & reproduces 1200 and 2400 Hz tones - Nothing more & nothing less.
The D1122 Micron Computer Program Data Recorder from Altronics proved to be quite reliable although their automatic rewind button release didn't always work.
Modern audio WAV players work reliably.
Indeed, I forgot to report back. My usual 'laptop with mono cable running Audacity' worked every time with the increased voltage so I'm a happy bunny. Just need to sort the sound now. As it happens, I do have several proper data recorder types, one with phase inversion, so if the laptop hadn't have worked I could have resorted to making cassettes again like the old days
Cheers
Witchy